Dairy Cattle

**This module is under construction. It will be updated with new content.**

This module consists of the following submodules:

Medicated Milk Replacer

Historically, many dairy cattle producers relied upon medicated milk replacer in their calf health management program. Although the use of medicated milk replacer is now more restricted as a result of the Veterinary Feed Directive, it is important for veterinary practitioners to understand the pros and cons of using medicated milk replacer in dairy calf management. This module describes the indications for medicated milk replacer, its role in the development of antimicrobial drug resistance, as well as management practices that help reduce the need for medicated milk replacer.

LEARNING OUTCOMES

This submodule aims to describe factors to consider in the use of medicated milk replacer. By the end of the module, you will be able to:

  1. Describe medicated milk replacer and how it is regulated under the Veterinary Feed Directive.
  2. Identify antibiotics that historically were most commonly added to medicated milk replacer.
  3. List the disadvantages associated with using medicated milk replacer.
  4. Describe proper management and preventive medicine that are critical to long-term calf health.
  5. Describe a good colostrum management program for dairy calves. 

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Farm Background

It is a Tuesday morning at the Dairy Solutions Veterinary Clinic. When Dr. Karl arrives, his receptionist meets him at the door with a message from local dairyman Chuck Erby regarding a continuing struggle with scours (diarrhea) in his calves.
When Dr. Karl returns the call, Chuck explains, “For the past two weeks I’ve had several scouring calves and some calves with pneumonia too. One calf died this morning, and several more look like they may die soon.” Chuck is calling for help treating the sick calves, but Doc knows that the long-term solution to Chuck’s problem requires improved management to help his calves stay healthy. Doc agrees to stop by later that morning.

Dr. Karl and a fourth-year veterinary student named Gretchen head out to visit Chuck and his calves. Dr. Karl explains that Chuck Erby is a long-time client who runs a small dairy operation with about 80 milking cows. [Note: Most dairy herds will have about as many calves and heifers as they have cows of milking age.] Over the past few years, Mr. Erby has had frequent problems with scours in his calves and usually treats these cases with antibiotics and supportive therapy such as fluids and electrolytes. Mr. Erby has almost no help in running his farm and has said he does not have time to make the management changes that Doc has recommended before.

Farm Tour

When they arrive, Gretchen sees that few updates or changes have been made to the original farm structures. The milk house is small and cluttered with various items including tools, drugs, cleaning solutions, and clothing. The tie-stall barn houses the milking herd and has poor lighting and ventilation. Cows are tied facing the walls on each side of the barn, and a walkway traverses the middle of the barn. A few calves are housed at one end of the tie-stall barn. Twice a day the cows walk by the calves on their way to the milking parlor.

Several abandoned calf hutches are just a few yards from the milk house. Gretchen recently learned in school that calf hutches are a good way to isolate calves from each other and the older cattle to reduce their exposure to opportunistic enteric and respiratory pathogens. [Note: Opportunistic pathogens are agents that can cause disease in the presence of the proper combination of contributory causes that are present on most farms.] Gretchen wonders if maybe Dr. Karl will attempt to convince Chuck to try using the calf hutches again, even if they may be more work.

Dr. Karl and Gretchen start looking at the calves. The bedding seems to have been recently changed—perhaps in anticipation of their visit. However, because the calves are dirty, Dr. Karl suspects that the level of sanitation for the calves has not been very good. The calves are not isolated from each other and are exposed to the milking herd twice a day when the cows take the concrete walkway to get to the milking parlor. Dr. Karl tells Gretchen that on previous visits he has told Mr. Erby to isolate the calves from each other and from the cows to prevent transmission of pathogens, but this clearly has not been done.

Gretchen reviews the farms medical history and noticed he was purchasing 50 lb bags of medicated milk replacer for his calves. Mr. Erby was using medicated milk replacer containing oxytetracycline and neomycin “to aid in the treatment of bacterial diarrhea (scours).” She remembers from lecture that neomycin, oxytetracycline, and chlortetracycline are the antibiotics most commonly added to medicated milk replacer. She asks, "Mr. Erby, do you always use a milk replacer that contains antibiotics?"

Medicated Milk Replacer

"I guess I didn’t realize my milk replacer had antibiotics,” replied Mr. Erby. Later, Gretchen learned that some dairy producers have been used to purchasing medicated milk replacer (milk replacer to which low levels of antibiotics have been added) without really understanding that the term “medicated” means that subtherapeutic levels (concentrations lower than what is needed for effective treatment of clinical disease) of antibiotics have been added. Other producers knew that medicated milk replacer contained antibiotics, but did not realize the concentrations were too low to treat clinical disease caused by bacteria such as E. coli and Salmonella. Gretchen mentioned that medicated feed can no longer be purchased over the counter according to the Veterinary Feed Directive (VFD) implemented on January 1, 2017. The usage of medically important antibiotics in animal feed (including milk replacers) requires veterinary oversight and bans the usage of antibiotics for the purpose of growth efficiency and disease prevention. Information on currently approved and no longer approved antibiotics for medicated milk replacer dispensed under the Veterinary Feed Directive may be found at the FDA.gov website.

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Intrigued, Gretchen wonders about the difference in price between medicated milk replacer and nonmedicated milk replacer. When she gets back to the veterinary clinic, she thumbs through a couple of pages in some farm catalogs and finds that the price from one company for a 50-pound bag of medicated milk replacer is $45.99 and nonmedicated is $39.99. That’s a difference of about 10 percent: using the nonmedicated milk replacer could save Chuck about $600 a year.

[Add some kind of box or notice giving a link to our (yet to be written) module on the VFD.]

Dr. Karl explains that medicated milk replacers used to have a label stating they are to be used for disease prevention and growth promotion, and on this basis were often thought to be an economically sound choice. Studies conducted under conditions of modern calf management in the 1990s, however, showed that medicated milk replacers were not highly useful for growth promotion (5, 6). In a 2006 study, Raymond (2) discussed several studies which had conflicting results regarding the benefits of medicated milk replacer, but pointed out that effective passive transfer in cattle is more effective in reducing calf morbidity and mortality compared with subtherapeutic feed additives. With respect to medicated milk replacer, Raymond (2) reports that more than two-thirds of farms in his Washington study were not using medicated milk replacer, illustrating that medicated milk replacer is not necessary to maintain calf health.

Dr. Karl tells Mr. Erby, “Preventing scours needs to start right at the birth of the calf. The calf should be isolated immediately from the dam and all other animals to prevent disease transmission. The calf should be given good quality colostrum within one to two hours of birth (4). The quality of colostrum can be assessed with a colostrometer to measure the immunoglobulin levels. Total immunoglobulin concentration of the colostrum should be greater than 60 mg/ml. A second feeding of colostrum should take place within 12 hours of birth. Maximum absorption occurs within the first 24 hours of life, so it is important to administer the good quality colostrum within the first 24 hours. After two feedings of good quality colostrum, you can then start feeding milk replacer or pasteurized milk.” Dr. Karl has been telling Mr. Erby that he should occasionally test his colostrum for immunoglobulin levels. The calf should receive the equivalent of about 10 percent of its body weight in colostrum each day. The amount of colostrum for each feeding should be two to four liters depending on the size of the calf. This quantity of colostrum will likely require the use of an esophageal feeder. Thereafter, calves should be fed milk or milk replacer at 10 percent of their body weight each day for six to eight weeks. The calves should also be supplied with free choice grain and water.

Calf Management

Recommendations:

  • Isolate the calf from the dam and other cattle at birth to prevent disease transmission. (Note that Chuck’s calves are constantly being exposed to manure from the adult cows and the other calves.)
  • Give good quality colostrum, ideally from mature cows. Assess the quality of the colostrum by using a colostrometer to measure the immunoglobulin level. Good quality colostrum has a total immunoglobulin concentration greater than 60 mg/ml. (Note that Chuck does not check his colostrum but just assumes the colostrum he feeds is of adequate quality.)
  • Ideally, the first feeding of colostrum should be given within one to two hours after birth. A second feeding of colostrum should be given within 12 hours after birth. All feedings of colostrum should be given within the first 24 hours of birth for maximum absorption. (Note that Chuck admits to not getting colostrum to his calves this quickly.)
  • Each time that colostrum is fed, give two to four liters, depending on the size of the calf. Give an 80 lb calf four liters of colostrum, which is approximately 10 percent of the calf’s body weight. Give a 60 lb calf three liters of colostrum, which is approximately 10 percent of the calf’s body weight. (10 percent body weight of an 80 lb calf is 8 lbs. 8 lbs = 128 oz = 4 quarts or 3.79 liters.)
  • Occasionally check the immunoglobulin level in the calf’s blood to assure that the colostrum has been properly absorbed. A reasonable goal for the immunoglobulin level in the blood is10 g/l. (Note: Chuck does not do this.)
  • After the first two feedings of colostrum, other milk (i.e., milk replacer or pasteurized milk from the bulk tank) can be fed.
  • Continue to feed milk to the calves twice a day for six to eight weeks. Give an 80 lb calf four liters of milk, which is approximately 10 percent of the calf’s body weight. Give a 60 lb calf three liters of milk, which is approximately 10 percent of body weight. (10 percent body weight of an 80 lb calf is 8 lbs. 8 lbs = 128 oz = 4 quarts = 3.79 liters.) The amount of milk or milk replacer should be adjusted as the calf grows.
  • Supply free-choice fresh grain and clean water.

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Medicated Milk Replacer

Gretchen asks Dr. Karl, “Besides the additional cost and low dose of antibiotics being used, are there any other disadvantages to using medicated milk replacer instead of nonmedicated milk replacer?”

Dr. Karl replies, “Any use of antibiotics can contribute to the development and maintenance of antimicrobial resistant bacteria. Such resistant bacteria may eventually lead to treatment failures on farms if antibiotics are needed for treating sick animals. Also, antimicrobial resistance genes may be transferred to human pathogens and can eventually find their way to people via direct animal contact or through meat or milk products. Another problem is that the use of medicated milk replacer can result in residues in meat, such as neomycin drug residues in veal (7)."

Dr. Karl continues, “Antibiotic resistance may develop more quickly when subtherapeutic levels of an antimicrobial are used, such as the low levels used in medicated milk replacer (8). High doses of antibiotics tend to kill the entire target bacterial population and can also kill most of the commensal bacteria. In contrast, low doses of antibiotics are more likely to select for bacterial subpopulations with antibiotic resistance traits, thereby allowing these subpopulations to survive and reproduce (8). These commensal bacteria are ‘innocent bystanders,’ but they can still develop resistance traits that can eventually be shared with their more pathogenic bacterial relatives and neighbors.”

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Sanitation and Hygiene

The next day while driving, Gretchen asks Dr. Karl, “How can over 40 percent of all dairy farms do just fine without ever using medicated milk replacer?”

Dr. Karl replies, “I like to encourage dairy producers to prevent scours and respiratory disease with the use of good sanitation and hygiene, proper nutrition, vaccination, appropriate ventilation, and a good colostrum program. Most dairy managers agree that it is more cost effective to prevent disease than to allow the calves to get sick and then try to treat them. Dairy producers that have good management practices with low rates of calf disease will usually not benefit from using a medicated milk replacer. The antibiotic resistance fostered by the unnecessary use of antibiotics makes it more difficult to treat future animal diseases and may contribute to the antibiotic resistance burden in animal agriculture and human medicine. Plus, medicated milk replacer costs more than nonmedicated milk replacer.”

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Module Summary (Medicated Milk Replacer)

  • Many producers used to purchase medicated milk replacer without recognizing that it contained antibiotics and without understanding that the dose of antibiotics was too low to treat common bacterial causes of calf scours or respiratory disease.
  • Use of medicated milk replacers can contribute to the dissemination of antimicrobial resistant bacteria, possibly causing treatment failures on farms or in human hospitals.
  • Almost half of US dairy producers have found that sound animal husbandry practices eliminate the need for the routine use of medicated milk replacers. They have found that it is more effective to prevent scours and respiratory disease in calves through management procedures such as sanitation, isolation and an adequate amount of high quality colostrum given within 24 hours of birth.

References (Medicated Milk Replacer)

  1.  USDA. 2005. Part IV: Antimicrobial Use on U.S. Dairy Operations, 2002. USDA:APHIS:VS:CEAH, National Animal Health Monitoring System, Fort Collins, CO #N430.0905. 
  2. Raymond MJ, Wohrle RD, and Call DR. 2006. Assessment and Promotion of Judicious Antibiotic Use on Dairy Farms in Washington State. Journal of Dairy Science. 89:3228-3240.
  3.  Biosecurity Practices of U.S. Dairy Herds. Info Sheet. Veterinary Services. USDA:APHIS:VS. May 1996. 
  4. Colostrum Feeding. APHIS Info Sheet. USDA:APHIS:VS:CEAH, December 2002.
  5. Morrill JL, Morrill JM, Feyerherm AM, and Laster JF. 1995. Plasma Proteins and a Probiotic as Ingredients in Milk Replacer. Journal of Dairy Science. 78:902-907.
  6. Quigley, JD III, Drewry JJ, Murray LM, and Ivey SJ. 1997. Body Weight Gain, Feed Efficiency, and Fecal Scores of Dairy Calves in Response to Galactosyl-Lactose or Antibiotics in Milk Replacers. Journal of Dairy Science. 80:1751-1754.
  7. Reminder - Medicated Milk Replacers Can Cause Antibiotic Residues in Bob Veal Calves. CVM Update. FDA:Center for Veterinary Medicine. July 29, 2004. 
  8. Berge AC, Lindeque P, Moore DA, and Sischo WM. 2005. A Clinical Trial Evaluating Prophylactic and Therapeutic Antibiotic Use on Health and Performance of Preweaned Calves. Journal of Dairy Science. 88:2166-2177.
  9. Heinrichs AJ, Wells SJ, and Losinger WC. 1995. A Study of the Use of Milk Replacers for Dairy Calves in the United States. Journal of Dairy Science. 78:2831-2837.
  10. Braidwood JC and Henry NW. 1990. Clinical efficacy of chlortetracycline hydrochloride administered in milk replacer to calves. Veterinary Record. 127:297-301.
  11. Schifferli D, Galeazzi RL, Nicolet J, and Wanner M. 1982. Pharmacokinetics of oxytetracycline and therapeutic implications in veal calves. Journal of Veterinary Pharmacology and Therapeutics. 5:247-57.
  12. Luthman J, Jacobsson SO, Bengtsson B, and Korpe C. 1989. Studies on the bioavailability of tetracycline chloride after oral administration to calves and pigs. Zentralblatt für Veterinärmedizin. Reihe A. 36:261-8.
  13. Palmer GH, Bywater RJ, and Stanton A. 1983. Absorption in calves of amoxicillin, ampicillin, and oxytetracycline given in milk replacer, water, or an oral rehydration formulation. American Journal of Veterinary Research. 44:68-71.
  14. NAHMS Dairy 2007. USDA:APHIS:VS Centers for Epidemiology and Animal Health, 2150 Centre Ave, Bldg B. Fort Collins, CO 80526.

Neonatal Scours, Antibiotics, and Dairy Calves

Calf management practices play a very important role in the health of dairy calves. As a part of antimicrobial stewardship, it is essential for veterinarians to understand the calf management practices that can reduce the need for antibiotics, which in turn may reduce the emergence of antimicrobial drug resistance. This module describes the presentation, treatment, and impact of calf scours, as well as health management practices that can avert or reduce the need for antimicrobial drugs in addressing this disease.

LEARNING OUTCOMES

This sub-module aims to introduce neonatal scours and antibiotic use in dairy calves. By the end of the module, you will be able to:

1. Describe the management practices that can prevent scours in calves, such as high quality colostrum management, sanitation and proper isolation procedures.
2. Explain the proper role of antimicrobial agents in treating calves with scours.

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Farm Background

while you were out message card

It was a busy Tuesday morning at the Dairy Solutions Veterinary Clinic. Dr. Karl, the owner, walked into the office and the receptionist immediately handed him a message from Chuck Erby, a local dairyman. The message said that Chuck wanted to talk to Dr. Karl about a diarrhea (scours) problem in his dairy calves.

Dr. Karl picked up the phone and called Mr. Erby. “Hey Chuck, this is Dr. Karl. I hear you have a scours problem. What’s going on?”

“For the past two weeks I’ve been treating several scouring calves with sulfa tabs and electrolytes—with little to no response. Now I have switched to tetracycline pills. To top things off, this morning I had one die and several are looking very sick,” Chuck responded.

“Sounds like you have your hands full. I will be out this morning to see what we can do. I’ll probably necropsy the one that died this morning,” Dr. Karl replied and hung up the phone. He grabbed his boots and keys, and then he and Gretchen headed to his truck.

Dr. Karl gave Gretchen an overview of Majestic Farms as they drove to investigate the calf diarrhea problem. Majestic Farms has been a family farm for over 50 years, and Mr. Erby is a longtime client of Dr. Karl. The farm is a small dairy with a 60-cow stanchion barn on 200 acres. In the past few years, Mr. Erby has had some problems with scours among the calves at Majestic Farms, but only a couple of calves have died of scours. Mr. Erby has tried various approaches to prevent scours, but little has worked. Despite the history of a scours problem, Mr. Erby has been reluctant to make improvements in his calf management as suggested by Dr. Karl.

dairy calf

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Calf Management

Currently, all calves receive a bottle of colostrum at birth for at least one feeding and then are placed on milk replacer which contains antibiotics. Multiple feedings of colostrum are not consistently provided to calves. There is no testing of colostrum to ensure that it is of adequate quality, and no testing of sera from the calves to validate adequate colostrum intake by the calves. Calves are tied to a wall or pen in the barn and receive ad-libitum grain, with a coccidiostat added by the manufacturer. Calves are not given milk or milk replacement products after approximately 60 days of age, at which time the calves are placed in group housing.

What Next?

Scours History

Majestic Farms has had a problem with scours among calves on the farm for the last two to three years, but typically the calves recover to good health. Today, the problem is a renewed concern because of the death of a five-week-old calf. The calf first became ill with scours about two weeks ago and was treated for 10 days with fluids with electrolytes, sulfa tablets and two injections of tetracycline. When the calf died, Mr. Erby realized he needed help and called Dr. Karl. According to Mr. Erby, 13 of 22 calves born in the last two months have become ill with scours. Mr. Erby treated all 13 calves, but feels that the antibiotics are not very effective because the symptoms persisted.

calf being fed

Calf Records

Examine the Calf Records: Like most producers, Mr. Erby writes down the calf's number followed by the treatment given.

February

Sunday

Monday

Tuesday

Wednesday

Thursday

Friday

Saturday

1

 

 

 

2

 

3

 

4

403 electrolytes

 

5

 

6

 

7

 

8

 

 

 

9

10

11

12

13

403 electrolytes +Sulfa

14

15

403

Sulfa

16

17

18

406  electrolytes

19

406  electrolytes

20

21

22

 

 

23

24

408  electrolytes  + Sulfa

25

26

407  electrolytes

408  electrolytes +Sulfa

27

28

29

 

 

 

 

 

 

 

 

 

 

 March

Sunday

Monday

Tuesday

Wednesday

Thursday

Friday

Saturday

 

 

 

1

407 electrolytes

2

3

409 -dead

4

 

5

 

6

7

 

 

8

 

 

 

9

10

11

12

13

14

 

 

15

408 Sulfa

16

17

408 Sulfa

18

19

20

413 electrolytes + Sulfa

21

413 electrolytes

 

22

413 electrolytes +Sulfa

23

24

25

26

27

28

 

 

29

30

415

electrolytes

31

415

electrolytes +Sulfa

 

 

 

 

 

April

Sunday

Monday

Tuesday

Wednesday

Thursday

Friday

Saturday

 

 

 

 

 

 

1

2

3

411

Oxytet +

electrolytes

4

 

 

5

411 Oxytet

6

7

8

412

Sulfa

9

10

11

421

electrolytes

 

12

13

14

420

Sulfa

15

16

420 Sulfa

17

18

414

electrolytes

 

19

20 417

electrolytes

414

electrolytes

21

22

417

electrolytes + Sulfa

23

24

417

electrolytes + Sulfa

25

 

 

26

417 Sulfa

420

electrolytes

27

415 electrolytes +Sulfa

28

417 Sulfa + electrolytes

29

417 Electrolytes

415 Sulfa

30

417 Oxytet +electrolytes

 

 

 

May

Sunday

Monday

Tuesday

Wednesday

Thursday

Friday

Saturday

 

 

 

 

 

 

 

 

1

417

electrolytes

2

407

Oxytet +

electrolytes

 

34

17 – dead

420

Oxytet +

electrolytes

4

Doc Karl Visits

5

6

7

8

9

 

 

 

10

11

12

13

14

15

16

 

 

 

17

 

18

 

19

 

20

 

21

 

22

23

 

 

 

24

25

26

27

28

29

 

 

30

 

 

 

31

 

 

 

 

 

Farm Tour

The farm buildings are original and few changes have been made to the structures. The milk house is small and cluttered with various tools and supplies. The medicine cabinet is packed with various pharmaceutical agents, cleaning solutions and other supplies. The poorly lit and ventilated tie-stall barn houses the 60-cow milking herd. A walkway traverses the middle of the barn and cows are tied facing the walls on each side. Three calves are tied at one end of the tie-stall barn, while 21 calves are in two pens on a manure pack and one end of the barn. Breeding-age heifers and dry cows are located outside in a wet and muddy lot, with a lean-to serving as protection from the weather.

Cows in a barn
calves tied up in barn

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Physical Exam

Prior to the death of the calf this morning, Mr. Erby had 22 calves less than 60 days of age, of which 13 have already been treated for scours. You perform physical examinations on the four calves that appear the most ill. The other ill calves have scours but do not appear as depressed.

 

CALF 1

CALF 2

CALF 3

CALF 4

Age

24 days old

68 days old

75 days old

80 days old

Sex

Female

Female

Female

Female

Temperature

101.5°F

104.0°F

100.5°F

103.0°F

Heart Rate

(Beats Per Minute)

110 BPM

150 BPM

100 BPM

140 BPM

Respiration Rate

(Respirations Per Minute)

36 RPM

70 RPM

40 RPM

66 RPM

Mucous Membrane Color and Feel

Pink, moist

Reddish, tacky-dry

Pale Pink, moist

Pale pink, tacky

Capillary Refill Time

1.0 seconds

1.0 seconds

2.0 seconds

1.5 seconds

Skin Tent and Percent Dehydration

Skin tent 1 second

 (<5% dehydrated)

 

Skin tent 3 to 5 seconds

(~10% dehydrated)

Skin tent 1 to 2 seconds

 (~5% dehydrated)

 

Skin tent 2 to 3 seconds

(~7 % dehydrated)

Alert Status

No depression

Depressed

No depression

Slight depression

 

Suckling Response

Good response

No response

Good response

Weak response

Appearance of Eye

No enophthalmia

Moderate enophthalmia

 

Minor enophthalmia

 

Minor enophthalmia

 

Diarrhea

Loose Stools

Loose bloody stools w/ pieces mucosa

Loose stools

Loose stools

Other

None

Sweaty, rough hair coat

Rough hair coat

Recumbent, anorexic

Diagnostic Specimens

Common infectious agents of calf scours include coccidia, coronavirus, Cryptosporidium, Escherichia coli, rotavirus, and Salmonella. Understand that any and all of these agents can cause scours when host immunity is low and environmental conditions create stress and high rates of transmission. These disease agents are mostly opportunistic, in that they are often present on farms with scours problems and also on farms without scours problems. Management and environment are often the factors that are most easily changed to control the disease problem.

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Necropsy

Dr. Karl says to Gretchen, “Don’t forget about biosecurity. You should not handle live calves after performing a necropsy because you could spread infectious agents from the dead calf to the live ones.”

Necropsy findings:

External Examination

  • Wet and soiled perineum region
  • Dull and rough hair coat
  • Thin calf

Internal Examination

  • Excessive peritoneal fluid
  • Fibrin tags over the intestines
  • Intestines were congested and fluid filled
  • Mesenteric lymph nodes were enlarged
  • Hemorrhages on the mesenteric lymph nodes
  • Intestinal contents were fluid to mucoid consistency, with some mucosal shreds and blood in the colon
  • All other organs appeared normal

To get a better understanding of what may be going on, the most severely ill calf was humanely euthanized and necropsied.

External Examination

  • Wet and soiled perineum region
  • Dull and rough hair coat
  • Thin calf

Internal Examination

  • Excessive peritoneal fluid
  • Intestines were congested and fluid filled
  • Thickened ileum and colon wall was slightly thickened with hemorrhage on the mucosa
  • The bowel felt thick when palpated and the intestinal vessels were congested

Antibiotic Selection

Empirical treatments are experience-based, therapeutic regimens generally administered prior to confirmatory diagnosis. Veterinarians rely on empirical antibiotic treatments when therapy is urgent and cannot wait for laboratory testing, but empirical treatments may fail when the pathogen has gained resistance.

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When to Use Antibiotics

Calves with bacteremia are candidates for antibiotic treatment. These calves are generally recognized by persistent systemic signs, such as fever, depression and lethargy. For example, depressed calves with a temperature above 104.0°F should probably be given an antibiotic. Clinical judgment is needed for deciding when to treat a calf that has a lower temperature. Importantly, calves should be treated with antibiotics only when it is necessary. Unnecessary antibiotic treatment creates a selective pressure for the dissemination of bacteria resistant to that particular antibiotic, and perhaps others that are genetically linked. Resistant bacteria can greatly complicate the treatment of scours.

Anti inflammatory drugs
Banamine can reduce fever and inflammation in calves and is indicated in cases with endotoxemia.

Fluids
Determine the amount of dehydration before administering fluids. Dehydration in a calf can be estimated by using a “skin tent” technique, assessing the appearance of the eye of the calf, and determining whether or not the calf is alert and has a suckling response. The skin tent technique is done by pinching and releasing the skin in the neck area and estimating the number of seconds it takes for the skin to return to normal. The appearance of the eye is assessed as normal or depressed (e.g., enopthalmia).

Appearance of calf

Percent dehydration

Calf standing and alert with a good suckling response and normal appearance of the eye; skin tent 5 seconds or longer

Mild dehydration:  5% or less dehydrated

Calf standing but depressed with no suckling response; eye appears depressed 5 millimeters or less; skin tent 6–7 seconds

Moderate dehydration:  6%–8% dehydrated

Calf lying on chest severely depressed without suckling response; eye appears depressed greater than 5 millimeters; skin tent greater than 7 seconds

Severe dehydration:  9%–11% dehydrated

Calf lying comatose on side, eye appears depressed; skin tent greater than 7 seconds

Critical dehydration:  12% or more dehydrated

Fluid Administration

If the calf has mild dehydration (5 percent or less dehydrated), fluids for rehydration can be administered orally or systemically (subcutaneously or intravenously). Fluids should be administered systemically if the calf has moderate or severe dehydration. After determining the administration route for rehydration therapy, decide what type of fluids to use for rehydration.

If the calf has mild dehydration (5 percent or less dehydrated), fluids for rehydration can be administered orally or systemically (subcutaneously or intravenously). Fluids should be administered systemically if the calf has moderate or severe dehydration. After determining the administration route for rehydration therapy, decide what type of fluids to use for rehydration.

Choosing the appropriate fluid for rehydration is determined according to the estimated osmolality and concentrations of sodium and potassium in the calf's serum. Lactated Ringer's, which best matches the electrolyte content, pH, and osmolality of serum, is the best choice for rehydration (when analysis of serum electrolytes are not available). Oral electrolyte solution is an excellent choice if the animal is less than 8 percent dehydrated and has a good suckling response. Electrolyte solutions contain sodium, potassium, chloride, bicarbonate, glucose, and glycine, and the majority have an alkalinizing ability.

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The three calves on this farm are given systemic rehydration and they perk up somewhat after receiving these replacement fluids. You decide to wait until the culture results are back to determine if antibiotics are necessary. As for the other calves that are ill with scours, it is best not to treat them with antibiotics since they are not depressed or dehydrated. Each calf should be monitored for any changes in clinical signs.

A recent study found that a treatment algorithm for calf diarrhea reduces antibiotic use in diarrheic calves by 80 percent, with no impact on calf health.1

fluid_administration_study

Recommended algorithm for treatment of diarrhoea in calves <30 days of age. 

If needed, administer oral electrolyte solution (OES) by tubing. BAR, bright, alert and responsive; NSAIDs, non-steroidal anti-inflammatory drugs; IV, intravenous; °T, temperature.1

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Calf Scours

  • Can be economically devastating to a producer
    • Increased morbidity and mortality of calves
    • Decreased growth of calves
  • Typically involve opportunistic pathogens
    • Opportunistic infections are usually caused by organisms that typically do not cause disease in healthy animals, but affect animals with a suppressed immune system
  • You can rarely diagnose a causative agent without clinical laboratory support
    • Remember that cases, or even healthy animals, may have two or more opportunistic pathogens diagnosed

Biosecurity

  • Use management procedures to prevent disease transmission
    • Handle calves by moving from youngest calves first, and working your way toward the oldest calves
    • Handle calves by moving from healthy calves to sick calves
  • Wear gloves when examining sick calves
  • Locate calf barns away from human and cow traffic
  • Minimize the number of people who go through the calf barn
  • Isolate the sick calves from all other animals

Fluid Therapy

  • Remember that diarrhea typically leads to metabolic acidosis and electrolyte imbalances
  • Types of fluids used:
    • If analysis of serum electrolytes is not available, choose a fluid that has similar electrolyte content, pH, and osmolality as does the body’s serum, e.g., lactated Ringer's solution
    • If analysis of serum electrolytes is available, choose the fluid type based on the sodium and potassium concentrations
    • Sodium concentration:
      • If sodium is normal, a balanced isotonic electrolyte solution for volume replacement should be used, e.g., NaCl
      • If sodium is decreased, a 0.9 percent isotonic saline solution should be used
      • If sodium is increased, a 2.5 percent dextrose in half-strength lactated Ringer's or saline, 0.45 percent saline, or 5 percent dextrose in water should be used
    • Potassium concentration
      • If potassium is normal, a balanced electrolyte solution should be used, e.g., NaCl
      • If potassium is decreased, lactated Ringer's should be used
      • If potassium is increased, 0.9 percent saline should be used
  • Routes of administration
    • Oral
      • Excellent for mild dehydration (5 percent dehydrated or less)
    • Subcutaneous
      • Used to deliver fluids over an extended time for mild dehydration
      • May be used with mild or moderate dehydration (8 percent dehydrated or less)
  • Intravenous
      • May be used for moderate dehydration (8 percent dehydrated or less)
      • Used for severe or critical dehydration (greater than 8 percent dehydrated)

Discussion with Client

Dr. Karl has sufficiently assessed the situation on the farm. He has collected specimens (blood and fecal matter) from three sick calves and specimens (fecal matter, intestinal contents, sections of large and small bowel, and mesenteric lymph nodes) from the two dead calves. He will submit these specimens to his state veterinary diagnostic laboratory.

Before leaving the farm, Dr. Karl instructs Mr. Erby to give one liter of lactated Ringer's solution under the skin (subcutaneously) and two liters of oral electrolytes two hours post-feeding, twice a day, to each of the three affected calves. Dr. Karl explains that the fluids replace the fluids, electrolytes, and bicarbonate lost with the diarrhea. He leaves Chuck two boxes of oral electrolytes to use for the next few days. Dr. Karl also tells Chuck to keep observing the other scouring calves for any changes in their clinical signs. Since they are not depressed or dehydrated, Dr. Karl thinks it would be best to only monitor these calves at this point.

Chuck may be disappointed that Dr. Karl is not going to give antimicrobial agents to all of the calves with scours. Dr Karl explains that giving antibiotics when treating an unknown disease could potentially make the situation worse. Empiric therapy with antimicrobial agents is only acceptable when systemic signs are present (fever, depression, lethargy).

Colostrum Management

Dr. Karl also discusses Chuck's management practices and how they might be updated. He stresses the importance of a good colostrum management program and ensuring that calves receive the highest quality colostrum at birth.

Key components to a colostrum management program:

  1. Quality: Give high-quality colostrum containing 50 mg/ml of IgG or with a specific gravity of > 1.010 using a colostrometer.
  2. Quantity: Give four liters of colostrum at the first feeding to achieve a serum immunoglobulin level of >1000mg/100ml, which can be tested 24 hours after feeding using an immunoglobulin snap-test. The snap-test measures the levels of immunoglobulins in the calves' blood. 
  3. Promptness: Feed colostrum within the first two to six hours of life.
  4. Cleanliness: Use fresh colostrum, collected by using clean milking technique and equipment, in order to minimize bacterial contamination.

Laboratory Results

ANIMAL DIAGNOSTIC CENTER
911 Incinerator Road
Big Town, WA 96742-4419

Later, Dr. Karl reviews the following results from the lab.

Submitter

Name: Dr. George Karl 

Date Received: Aug 16

Address: 213 Miller Road  

Address: 213 Miller Road  

City: Shilo

State: WA

Zip: 89317

Specie: Bovine

Breed: Holstein

Age: 1−3 month

 

 

  Laboratory Results

Calf 1

Calf 2

Calf 3

Calf 4

 

Fecal Float Results

 

 

One to two

coccidia per

high power

field

 

Rare strongyle

egg, several

cryptosporidia

 

 

One coccidium

per high power

field

 

cryptosporidia

 

 

 

 

Fecal Smear Results

Normal

 

 

cryptosporidia

 

Normal

 

cryptosporidia

 

Rota/Coronavirus

ELISA Results

Negative

 

Negative

 

Negative

 

Negative

 

Fecal Culture

Results

 

 

 

 

 

 

 

 

 

 

 

Negative

 

 

 

 

 

 

 

 

 

 

 

 

Salmonella

Susceptibility

R=Amoxicillin,

Ampicillin,

Neomycin,

Gentamicin,

Streptomycin,

Tetracycline

S=Trimethoprim-

Sulfamethoxazole

MIC  <2/38 µg/ml

 

Negative

 

 

 

 

 

 

 

 

 

 

 

 

Salmonella

Susceptibility

R= Amoxicillin,

Ampicillin,

Neomycin,

Gentamicin,

Streptomycin,

Tetracycline

S=Trimethoprim-

Sulfamethoxazole

MIC <2/38 µg/ml

 

 

 

 

 

Necropsy Results:

Calf #1 that died prior to Dr. Karl’s arrival:

  • Rota/coronavirus ELISA negative
  • Histopathology of the tissues is still pending
  • Cultured Salmonella from intestines

Calf # 2 that was euthanized after Dr. Karl’s examination:

  • Rota/coronavirus ELISA negative
  • Histopathology of the tissues still pending

Comments:

  • Report Sent: Aug 19
  • Likely Pathogens: Crytosporidium and Salmonella

Treatment Plan

Later in the week, Dr. Karl stops by the farm to see Chuck and to share the diagnostic laboratory results. “Chuck, I am fairly confident that we are dealing with a Cryptosporidium problem on your farm, which is complicated by an occasional Salmonella infection,” Dr. Karl explains. Since both of these agents are zoonotic, Dr. Karl cautions Chuck to use personal protection (e.g., gloves) and good hygiene (e.g., hand washing) when working with the calves.

Dr. Karl continues, “The Salmonella strain isolated from your calves is multidrug resistant. This means that one or more of our antibiotics will not be effective. The resistance of this bacterium may be due, in part, to the previous use of antibiotics. This secondary Salmonella infection was probably the cause of the first calf's death.”

“All right,” says Chuck. “So what do we do to treat these calves and make them feel better?”

With regret Dr. Karl says, “The underlying cause of the scours in your calves is Cryptosporidium. Unfortunately, no specific treatment will eliminate this protozoa. Therefore, the only treatment is supportive therapy, including fluids and oral electrolyte solutions. Furthermore, to control Cryptosporidium and prevent its spread to other calves, management changes are essential such as isolating sick calves, cleaning the environment, and using an all-in-all-out system for raising calves.

Common Pathogens in Calf Scours

Facts about Cryptosporidium and Cryptosporidiosis

  • Caused by protozoan
  • Can infect most domestic mammals
    • Found commonly in calves less than four weeks of age
  • Zoonotic
    • Outbreaks occur among veterinary caregivers
  • Clinical signs in calves:
    • Diarrhea (loose to watery)
    • Tenesmus
    • Blood and/or mucus in stool
    • Bile color in stool
  • High morbidity (>30%), low mortality (<5%)
  • Pathogenesis:
    • Invade enterocytes in distal small intestines and large intestines
    • Live just under cell membrane
    • Destroy villi, which can lead to villi fusion
    • Oocyst excystion begins with the first signs of diarrhea, therefore infected animals should be isolated as soon as possible to hinder transmission and prevent shedding and contamination of the environment

Facts about Salmonella

  • Typically disease of dairy and veal calves
  • Typically causes infection in calves less than four weeks of age
  • Zoonotic
  • Can be subtyped by serotyping:
    • Common serotypes of cattle include Typhimurium, Newport, and Dublin
  • Clinical signs:
    • Depressed
    • Fever
    • Profuse diarrhea
    • Swollen joint(s)
  • Low morbidity (<10%), high mortality (>50%)
  • Commonly resistant to several antimicrobial agents
  • Pathogenesis:
    • Colonize distal small intestine or colon
    • Fimbriae attach to enterocytes
    • Invade and destroy cells
    • Carrier state is possible

Management Recommendations 

With that, Dr. Karl leaves Chuck to ponder the possible management changes he can make around the farm.

light bulb  Now it's time to Check Your Understanding of your comprehension of this section.

Dr. Karl says, “Do you have any thoughts on improving the management of your calves and heifers?”

As Chuck comes to grips with admitting that changes need to be made on his farm, he goes into great detail about how he has already improved calf housing at the end of the barn. “I have already cleaned it, put lime down, and added fresh bedding. I found a water pipe leaking and have fixed that, so the soil will hopefully dry up. I am going to fence in a yard and try to keep the bedding dry and clean.”

Dr. Karl is pleased to hear Chuck has already made some changes, but he also hopes Chuck realizes that there are still many other things that need to be done to improve biosecurity and preventive medicine practices on his farm. Chuck stands by, looking somewhat pleased with his effort, but still confused. ”So… are you going to give me some antibiotics for these little guys, or what?”

Dr. Karl now realizes that he has not communicated as well with Chuck as he thought. "No, Chuck! Antibiotics may be helpful for a few individual sick calves with evidence of systemic infection, such as high fever. Antibiotics are not necessary for the other calves that have scours with no other symptoms. We have to look to improved management to help them, and try to prevent these types of infections from occurring in the future.”

Chuck sputters, “When is using an antibiotic beneficial and necessary?”

Dr. Karl explains that antimicrobial treatments should be reserved for when an animal shows signs of a systemic infection (elevated temperature, off feed/depressed) that is likely due to a bacterial infection. When choosing an antimicrobial treatment, culture and susceptibility testing should be performed to ensure the appropriate antimicrobial treatment is being used. Empiric therapy can be initiated while waiting for laboratory results to come back if systemic signs are present. Oxytetracycline is labeled for the treatment of calf scours.

You are not really helping your client by focusing on which antimicrobial treatment(s) to use for calves with scours. Calves with diarrhea die from dehydration, electrolyte losses, and metabolic acidosis. Fluid and electrolyte replacement should be the mainstay of treatment for diarrhea. The ultimate solution for calf scours lies in preventive medicine, specifically in improving management practices.

As of November, 2017, the Centers for Disease Control and Prevention are investigating an ongoing 2-year, 15-state outbreak of multidrug-resistant Salmonella Heidelberg infections in people linked to sick dairy calves.
Follow this link for more information: https://www.cdc.gov/salmonella/heidelberg-11-16/index.html

Module Summary (Neonatal Scours, Antibiotics and Dairy Calves)

  • Short-term treatment and control of scours is often difficult. Antimicrobials should only be used for scours when an individual calf is showing signs of a systemic infection. Rehydration is the most effective treatment for scours.
  • Proper management can go a long way to control scours (clean maternity pens, quality colostrum management, good milk replacer, individual isolated hutches, proper vaccinations, good biosecurity measures, and isolation of new or sick animals). The quality and quantity of colostrum given within the first six hours of birth is crucial to getting calves off to a good start. Have a high-quality colostrum management program and place the calf in a clean, stress-free environment to reduce the likelihood of them becoming sick and needing antimicrobial treatments.
  • By following these guidelines, you will be providing the calves with a clean, low-stress environment and adequate nutrition to fight off opportunistic infections when they occur.
  • Keys to preventing scours in calves:
    • Employ an excellent colostrum management program.
    • Cleanliness is essential in maternity pens, hutches and calf stalls.
    • Caretakers must employ proper hygiene to prevent transmission among calves.
    • Provide an adequate level of nutrition in milk replacer and grain.
    • Fresh clean water should always be available.
    • Reduce stress and transmission with a comfortable environment—spacious, dry, clean, and ventilated.
    • Employ consistency in caretaker duties and feeding schedules.
    • Use an appropriate vaccination program for calves.
    • Regulate the traffic flow—very few people need access to the calf-raising area. When examining or caring for calves, reduce transmission of disease agents by moving from young to old and/or from healthy to ill.

References (Neonatal Scours, Antibiotics and Dairy Calves)

1. Gomez, Diego E., Luis G. Arroyo, Zvonimir Poljak, Laurent Viel, and J. Scott Weese. "Implementation of an algorithm for selection of antimicrobial therapy for diarrhoeic calves: Impact on antimicrobial treatment rates, health and faecal microbiota." The Veterinary Journal 226 (2017): 15-25.

Model Mastitis Control Program

Antibiotics are commonly used in the treatment of mastitis in dairy cows, and dairy practitioners play an important role in implementing antimicrobial drug stewardship in this industry. This module provides guidance on the judicious use of antibiotics in the treatment of mastitis in dairy cows. Common mastitis pathogens are discussed, as are factors to consider when selecting an antibiotic drug, as well as management measures that can help prevent mastitis in dairy cows.

LEARNING OUTCOMES

This submodule outlines a mastitis management program that can serve as a model for dairy practitioners. By the end of the module, you will be able to:

  1. Discuss the general guidelines for the judicious use of antibiotics in the treatment of mastitis.
  2. Describe the factors to consider in the selection of an antimicrobial drug for mastitis treatment.
  3. Outline the preventive measures that may be taken on a dairy farm with regards to mastitis.

--This module is under construction. New content coming soon.--

Mastitis Prevention and Control in Dairy Cows

The management of contagious mastitis presents many challenges to the dairy farm veterinarian, including incorporating antimicrobial stewardship into the treatment plan. This module outlines the pathogens, diagnosis, and treatment of contagious mastitis and details the judicious selection of antibiotics for this disease. Alternative control measures and preventive practices that reduce the need for antibiotics are also addressed. 

LEARNING OUTCOMES

This submodule aims to describe a treatment plan for contagious mastitis that incorporates antibiotic stewardship. By the end of the module, you will be able to: 

  1. Discuss proper indications for the use of antimicrobials for contagious mastitis in dairy cattle.
  2. Demonstrate understanding of the need to follow proper treatment protocols when using an antibiotic to treat individual cows for contagious udder pathogens.
  3. Explain how somatic cell counts and culture results are used to formulate a herd antibiotic treatment plan for contagious udder pathogens.
  4. Describe how antimicrobial treatment of contagious udder pathogens can be greatly reduced in herds by using effective mastitis prevention and control programs. 
  5. Recognize the futility of using antibiotics to treat cases of contagious mastitis if the cow is to be returned to a herd where she will quickly become reinfected.

Quick Navigation Links:

Contagious Mastitis

Dr. Susan Keller is having a typical day in her active dairy veterinary practice. Her cell phone rings, and she speaks with Mr. Oliver McCormick who owns and operates a dairy farm of about 150 milking cows.

“I’m having some mastitis problems," Oliver says. "You know we’ve talked before about my trying to lower my herd’s somatic cell count (SCC) to get a bonus from the creamery? Well, my last two counts have been over 300,000 cells per milliliter! So it’s getting worse instead of better. I think I’d like to treat all the infected cows with antibiotics so that my SCC comes back down."

“It sounds like you may have a mastitis problem going on there. I will be coming to your place for your routine herd check next Tuesday. Let’s plan on spending some time developing a plan to lower your herd’s SCC. ”

The following Tuesday at Oliver’s dairy farm:

After Dr. Keller finishes the routine pregnancy checks, she talks to Oliver about the possible mastitis problem in the herd. She checks both the latest farm DHIA report and the bulk milk tank SCC (bSCC) report from the milk processor.

Looking at the DHIA report, Dr. Keller reminds Oliver that the SCC for each individual cow is a measure of the degree of subclinical mastitis in that cow. It is estimated that each doubling of the somatic cell count by an individual cow results in the loss of about 1.5 pounds of milk production each day by that cow (6). A farm Dairy Herd Information Association (DHIA) report includes reports for each cow and a summary report for the entire herd. Also included are statistics relating to milk production and SCC and a linear SCC score that is a logarithmic transformation of the SCC score. The SCC linear score is linearly related to lost milk production and is useful in making management decisions since it reflects how much milk is being lost due to udder infection.

Somatic cell count linear score:

A somatic cell count linear score is a log2 transformation of the SCC score. Each one unit increase in the linear score is associated with a doubling of the somatic cell count, and an estimated loss of 1.5 pounds of milk production per day (6).

Purpose of somatic cell counts:

  1. Identify individual cows affected with subclinical mastitis.
  2. Monitor herd improvement after management changes are instituted.
  3. Identify herd mastitis problems as soon as possible.

Interpretation of somatic cell count linear score for an individual cow:

  • 0 and 1: no evidence of subclinical mastitis
  • 2 : low suspicion of subclinical mastitis
  • 3 and 4: suspect for subclinical mastitis
  • ≥ 5: subclinical mastitis
  • 7−9: indicates that the cow is shedding extremely high numbers of somatic cells and is on the verge of showing signs of clinical mastitis.

A herd goal should be to have >80 percent of the animals with SCC linear scores ≤3.

As another way to look for evidence of subclinical mastitis in the herd, Dr. Keller checks the bulk milk tank SCC report. A reasonable goal for bulk milk tank SCC is < 200,000 cells per ml. Federal and state regulations require that consumers not purchase Grade A milk from dairies that have a bulk milk SCC > 750,000 cells per ml. Dr. Keller confirms that the bulk milk tank SCC has been slowly increasing and is now > 300,000 cells / ml.

light bulb  Now it's time to Check Your Understanding of your comprehension of this section.

Common mastitis pathogens (2):

  • Staphylococcus aureus
  • Streptococcus agalactiae
  • Streptococcus uberis
  • Streptococcus dysgalactiae
  • Escherichia coli
  • Klebsiella sp.
  • Coagulase negative staphylococci

Less common mastitis pathogens:

  • Corynebacterium bovis
  • Mycoplasma spp.
  • Pseudomonas aeruginosa
  • Pasteurella multocida
  • Serratia marcescens
  • Bacillus sp.
  • Nocardia

Contagious Udder Pathogens (2):

  1. Streptococcus agalactiae
  2. Staphylococcus aureus
  3. Mycoplasma spp.
  4. Corynebacterium bovis
  5. Common characteristics of the contagious udder pathogens:
    • Infection with these pathogens primarily results in subclinical udder infection (except Mycoplasma bovis which may also cause outbreaks of clinical mastitis)
    • Primarily infect the gland after colonization of the skin (or from bacteremia in the case of Mycoplasma bovis).
    • These pathogens commonly infect the gland via teat impact (moving up the teat canal) if the milking equipment is not functioning properly.
    • Treatment of cows infected with these contagious udder pathogens is often thwarted because cured cows will likely get re-infected quickly unless management changes are adopted to prevent cow-to-cow transmission.

Environmental Udder Pathogens (3):

  1. Coliforms: Escherichia coli, Klebsiella, Enterobacter
  2. Streptococcus spp. (other than S. agalactiae)
  3. Coagulase negative Staphylococcus spp. (other than S. aureus) (these are more likely to be resident skin flora)
  4. Other Gram-negative rods (Pseudomonas, Proteus)

Environmental Udder Pathogens are:

  • The primary cause of clinical mastitis
  • May also cause subclinical mastitis
  • Also transiently colonize the skin on the teats and udders

Examples of mastitis pathogens with identified environmental risk factors (3)

  • Pseudomonas: Are associated with contaminated water from wash hoses or hot water heaters.
  • Klebsiella: Are associated with sawdust or shavings used as bedding.
  • Streptococcus uberis: Are associated with straw bedding.

Dr. Keller then asks to see the herd treatment records that Oliver maintains. The records indicate that at least 25 percent of the herd was treated for clinical mastitis at least once during each lactation period. Dr. Keller explains that a 25 percent rate of clinical mastitis is typical for most dairy farms, and indicates that this herd’s problem with high SCC is likely due to subclinical mastitis and not due to excessive clinical mastitis. 

Dr. Keller: “I see that 30 percent of your cows have a SCC linear score of  ≥5. This means that your bulk milk tank somatic cells are not coming from just a few cows, but that many cows are contributing to your high SCC problem. Furthermore, I see that only 54 percent of your cows have a somatic cell count linear score of  ≤3. A reasonable goal for you would be a linear score of  ≤ 3 for >80 percent of the cows in your herd. The DHIA report also compared each cow’s SCC linear scores from this month with those on last month’s report, and I see that a high proportion of the cows with high SCC linear scores this month did not have high scores last month. This means that they were recently infected and your problem is expanding.” 

SCC Chart

Legend:  This graph compares each cow’s SCC linear score from the current month to the SCC linear score from the previous month. It is used to indicate new infections, recovered infections, and chronic infections.

light bulb  Now it's time to Check Your Understanding of your comprehension of this section.

Dr. Keller shows Oliver the chart, pointing out the cow identification numbers in the upper left quadrant that have new infections. These are the cows that had low SCC linear scores last month and high ones this month.

“Are these the cows we are going to treat with antibiotics?” Oliver wants to know.

Dr. Keller says, “You have the right idea, but we only want to treat the cows that have a high likelihood of treatment success. Also, limiting antibiotic use will help prevent antibiotic resistance and thereby preserve the usefulness of antibiotics for the future.

“There are some cows in this group that are poor candidates for treatment. Plus, we need to know what types of bacteria are causing these infections before we select an antibiotic. For infections caused by the bacteria that we call ‘contagious udder pathogens,’ cows that are cured with an antibiotic treatment will just get infected again unless we make some management changes to prevent cow-to-cow transmission.”

Staphylococcus aureus (4)

  1. Can survive inside white blood cells (intracellular).
  2. Intermittently shed from the mammary gland, so milk must be cultured repeatedly to be sure a cow is truly negative.
  3. There is a 75 percent chance of detection with one culture from an infected cow.
  4. There is a 95 percent chance of detection with three cultures collected on consecutive days from an infected cow.
  5. In chronic cases, fibrosis and micro-abscess formation in the udder decrease the probability of adequate drug distribution to the site of infection.

 

Streptococcus agalactiae (4)

  1. Colonizes the epithelial surface of teat ducts.
  2. The udder is the reservoir of infection.
  3. Toxin elaboration results in inflammation.
  4. Organisms are shed in the milk in high numbers.
  5. Antibiotic therapy for lactating cows is highly successful provided the bacteria are not resistant to the antibiotic used.

Dr. Keller continues, “Not only will the culture results give us guidance regarding which antibiotic to use, the culture results can also help identify preventive procedures for your mastitis problem. Our first step will be to culture the cows with the highest SCC linear scores so we can tell which bacterial species are causing your SCC problem.”

Dr. Keller obtains milk samples from all cows with a SCC linear score of over 5 and sends them to the state veterinary diagnostic lab for culture.

The following week, Dr. Keller reports the culture results to Oliver McCormick

Cow culture chart

Dr. Keller continues, “You have several different kinds of bacteria that are responsible for your subclinical mastitis problem. About 55 percent of the cows with high SCC linear scores are infected with Staphylococcus aureus and 30 percent have Streptococcus agalactiae.

Staphylococcus aureus and Streptococcus agalactiae infections are considered to be ’contagious udder pathogens.’ Infection with these pathogens is usually strongly associated with milking technique, and they are spread from cow to cow. Even if you cure a cow, she will likely be immediately reinfected from one of her herd mates.”

Dry Cow Therapy (4)

  1. “Dry Cow Therapy” (DCT) refers to a long-acting antibiotic intramammary infusion administered after the last milking of a lactation, and therefore immediately before her “dry period.” The dry period is usually about two months long and therefore DCT starts when the cow is approximately seven months pregnant. 
  2. Dairies that have successfully controlled mastitis by proper management might only use antibiotic dry cow treatments for those select cows that appear to be subclinically infected with mastitis pathogens, or use selective therapy in combination with internal teat sealants. 
  3. Dairy farms with high rates of subclinical and clinical mastitis in early lactation should routinely administer an antibiotic dry cow treatment to all their cattle at drying off.

Dr. Keller says, “The next step is to determine what antibiotic will likely be effective against the strains of Staphylococcus aureus and Streptococcus agalactiae that you have circulating in your herd. We call this profile of antibiotic resistance an ’antibiogram,’ and it can be used for selecting the type of antibiotics that are most likely to be effective. We want to give strong preference to the older antibiotic products that are approved for use in lactating dairy cattle, that do not interfere with antibiotics commonly used for human medicine, and yet should be effective in killing the bacterial strains prevalent in your herd. This will help preserve the efficacy of antibiotics for the future.

“The good news is that you can eliminate these two pathogens from your herd, and with proper management and biosecurity programs, you can keep these pathogens out of your herd.

“The most important factors for preventing these infections relate to the milking procedure. To make sure your milking equipment is operating properly, I’d like to have your milking equipment checked out by your dealer. Then I will return when the cows are being milked to evaluate the milking techniques used in your milking parlor.”

Milking Equipment Performance and Use (5)

  1. Milking equipment function must be optimal to avoid transferring pathogens from one cow to another.
  2. Improperly functioning milking equipment can lead to teat end impact, which occurs during milking when milk jets back up the teat canal, potentially carrying pathogens that can establish an udder infection.
  3. Poorly operating milking equipment can also be traumatic to the teat skin and streak canal, thereby predisposing to infection.

A couple of days later, Dr. Keller returned to the farm during the afternoon milking. The equipment dealer had left a report stating that the milking system was operating at an optimal level. 

The following assessment was made of their milking procedure.


assessment

Dr. Keller asks Oliver to use 1 percent iodophor teat dip rather than a teat spray that often does not cover the backside of the teat.

Once again, Oliver asks the inevitable question, “Now that we know what bacteria are causing the problem, which cows do we treat with antibiotics?” Oliver adds, “Since the cows that are infected with Streptococcus agalactiae are more likely to respond to antibiotic treatment, can we start injecting those first?”

“Yes, we should treat the cows infected with Streptococcus agalactaie, but we should not use an injectable antibiotic. The abscess and scarring in the mammary gland reduces the ability of injected drugs from reaching the site of infection. Whenever possible we should use antibiotics according to their approved label directions, and there are no antimicrobial agents approved for subcutaneous, intramuscular or intravenous administration for the treatment of mastitis in dairy cattle. We will use an intramammary antibiotic. With Streptococcus agalactiae infections, we can expect a high cure rate (~90%) using an intramammary antibiotic. There is no need to give injectable antibiotics that may be less effective.”

light bulb  Now it's time to Check Your Understanding of your comprehension of this section.

Possible antibiotic treatments for Streptococcus agalactiae

  • Intramammary penicillin
  • Intramammary amoxicillin
  • Intramammary cephapirin
  • Intramammary pirlimycin
  • Intramammary ceftiofur

Poor antibiotic choices for Streptococcus agalactiae

  • Intravenous oxytetracycline
  • Intramuscular oxytetracycline
  • Intramammary gentamicin
  • Subcutaneous florfenicol
  • Intramuscular ceftiofur

Dr. Keller: “The more difficult problem is Staphylococcus aureus. To control Staphylococcus aureus, we need to identify the cows that have only recently been infected because these are the best therapeutic candidates. Chronic infections—which we identified earlier based on SCC linear scores—have a much lower likelihood of responding to treatment. Cows that are chronically infected with Staphylococcus aureus are very difficult to cure by antibiotic treatment because of the micro-abscesses and scar tissue that this particular organism causes in the mammary tissue. We only want to use antibiotics for those animals that are most likely to respond. Most cows that are chronically infected should be culled. If we do not identify the chronically infected cows and just treat all the cows with antibiotics, the chronically infected cows will not be cured and will remain a source of the Staphylococcus aureus for other cows in the herd. Finally, the infected cows that are not culled should be segregated from the rest of the herd and milked last, or with separate equipment, to prevent spread to the rest of the herd. Cows should receive our intramammary treatment. In order to avoid antibiotic residues, we do not want to treat cows that are about to be culled due to low production, old age or other problems. Chronically infected cows are much less likely to respond to treatment and are more likely to become reinfected, so these cows should probably be culled instead of treated. Cows that are late in lactation should be dried off a few weeks earlier than originally planned, and given an antibiotic dry treatment instead of an antibiotic licensed for lactating cows.”

sagittal section of a cow’s udder
A picture of a sagittal section of a cow’s udder to demonstrate distribution of a dye administered by intramammary infusion, in the front quarter (nonmastitic, left of red line) or the rear quarter (mastitic, right of red line). The front resulted in widespread diffusion of the dye, while the dye poorly diffused in the rear quarter. The limited diffusion of the dye in the mastitic quarter is due to fibrotic change and abscess formation. This demonstrates why some forms of mastitis are not easily treated with antibiotic intramammary infusions. 

Which cows infected with Staphylococcus aureus (Staph) or Streptococcus agalactiae (Strep ag) are good candidates for antibiotic therapy?

light bulb  Now it's time to Check Your Understanding of your comprehension of this section.

Mastitis Treatment and Prevention

Summary of Mastitis Antibiotic Treatment Guidelines:

  1. Use antibiotics to eliminate an infection, not to just reduce the signs of infection. 
  2. It is important to maintain a sufficiently high antibiotic concentration at the site of infection.
  3. If not responding well, consider using approved drugs with increased dose frequency and duration of therapy rather than quickly resorting to last-resort, broad-spectrum antibiotics. 
  4. Culture and test the identified organisms for antibiotic resistance by determining the mean inhibitory concentration (MIC), which can also be helpful in determining the correct dosage to administer. If you use systemic therapy, calculate the regimen based on the unique pharmacological parameters of the antibiotic and the MIC of the bacteria you are trying to kill.

Remember that treating cows with antibiotics should be a small part of your mastitis control program. The long-term solution lies in changing your management to prevent transmission. Many herds have completely eliminated both Staphylococcus aureus and Streptococcus agalactiae from their herd by following some simple management procedures.

Prevention and Control of the Contagious Udder Pathogens:

1. Proper milking technique in the parlor to prevent teat injury and cow-to-cow transmission of pathogens

      • Proper management to prevent cow-to-cow transmission of pathogens by fomites
      • Routine use of individual cow, disposable paper towels (versus cloth towels) for cleaning the teat
      • Trimming long udder hair
      • Automatic back flush system used after each milking

2. Routine use of germicidal teat dip applied after milking

      • Iodine—high (1%) and low (0.1–0.25%) concentrations
      • Chlorhexidine
      • Quaternary ammoniums
      • Sodium hypochlorites/Clorox—very irritating
      • Anionic acids (naturally occurring soaps)

3. Antibiotic dry cow therapy used according to label specifications
4. Treatment of cases of acute clinical mastitis
5. Cull cows with chronic infections
6. Keep infected cows segregated and use separate milking equipment to prevent transmission throughout the herd

Potential causes of teat trauma:

  1. Inappropriate vacuum: A vacuum level of 10.5−12.5 inches at the teat end during peak milk flow offers the best combination of rapid, complete milk removal with a minimal amount of physical harm. (A vacuum gauge should read 15 inches of mercury or 50 kilopascals)
  2. Inadequate massage: A cycle refers to the total time in seconds that a pulsator takes to complete one milk phase and one massage phase. The massage phase is the ‘rest phase’ of the milking process, and should not be less than 0.35 sec. The second phase is the ‘milking phase.’ Together the two phases are called the pulsator cycle.
  3. Pulsation ratio: Usually 50:50 or 60:40: The pulsation ratio is the length of time in each cycle that the pulsator is in its milk phase compared to its massage phase.

Module Summary (Mastitis Prenvention and Control in Dairy Cows)

Key points regarding the use of antibiotics for subclinical mastitis caused by contagious udder pathogens:

  • Remember that treating cows with antibiotics should be a small part of your mastitis control program. Limiting antibiotic use will help prevent antibiotic resistance and thereby preserve the usefulness of antibiotics for the future.
  • Culture milk samples from cows with high somatic cell count linear scores to determine the causative agent and its antibiotic resistance pattern.
  • Do not waste antibiotics by treating lactating cows that will soon be culled or dried off. 
  • Give strong preference to antibiotic products that are approved for use in lactating dairy cattle.
  • It is futile to treat infected cows with antibiotics if you do not take management steps to decrease the rate of transmission of contagious mastitis pathogens among the cattle. Otherwise, the cattle you treat today will be reinfected tomorrow.

References (Mastitis Prevention and Control in Dairy Cows)

  1. Erskine, RJ. 2001. Mastitis Control in Dairy Herds. Herd Health: Food Animal Production Medicine, third edition, edited by OM Radstits. WB Saunders, Philadelphia, Pennsylvania.
  2. Fox, LK and JM Gay. 1993. Contagious Mastitis in Update on Bovine Mastitis, Veterinary Clinics of North America, 9:475−487.
  3. Smith, KL and JS Hogan. 1993. Environmental Mastitis in Update on Bovine Mastitis. Veterinary Clinics of North America, 9:489−498.
  4. Erskine, RJ, SA Wagner, and FJ DeGraves. 2003. Mastitis therapy and pharmacology. Veterinary Clinics of North America: Food Animal Practice, 19(1):109−138.
  5. Dahl, JC, BD Harrington, and JA Jarrett. 1993. Contagious Mastitis in Update on Bovine Mastitis. Veterinary Clinics of North America, 9:531−536.
  6. Bartlett, PC, GY Miller, CR Anderson, and JH Kirk. 1990. Milk Production and Somatic Cell Counts in Michigan Dairy Herds. Journal of Dairy Science. 73:2794−2800.
  7. USDA. 2005. Part IV: Antimicrobial Use on U.S. Dairy Operations, 2002. USDA:APHIS:VS:CEAH, National Animal Health Monitoring System, Fort Collins, CO #N430.0905.
  8. Raymond, MJ, RD Wohrle, and DR Call. 2006. Assessment and Promotion of Judicious Antibiotic Use on Dairy Farms in Washington State. Journal of Dairy Science. 89:3228−3240.
  9. Biosecurity Practices of U.S. Dairy Herds. Info Sheet. Veterinary Services. USDA:APHIS:VS. May 1996. 
  10. Colostrum Feeding. APHIS Info Sheet. USDA:APHIS:VS:CEAH, December 2002.
  11. Morrill, JL, JM Morrill, AM Feyerherm, and JF Laster. 1995. Plasma Proteins and a Probiotic as Ingredients in Milk Replacer. Journal of Dairy Science. 78:902−907.
  12. Quigley, JD III, JJ Drewry, LM Murray, and SJ Ivey. 1997. Body Weight Gain, Feed Efficiency, and Fecal Scores of Dairy Calves in Response to Galactosyl-Lactose or Antibiotics in Milk Replacers. Journal of Dairy Science. 80:1751−1754.
  13. Reminder—Medicated Milk Replacers Can Cause Antibiotic Residues in Bob Veal Calves. CVM Update. FDA:Center for Veterinary Medicine. July 29, 2004. 
  14. Berge, AC, P Lindeque, DA Moore, and WM Sischo. 2005. A Clinical Trial Evaluating Prophylactic and Therapeutic Antibiotic Use on Health and Performance of Preweaned Calves. Journal of Dairy Science. 88:2166−2177.
  15. Heinrichs, AJ, SJ Wells, and WC Losinger. 1995. A Study of the Use of Milk Replacers for Dairy Calves in the United States. Journal of Dairy Science. 78:2831−2837.
  16. Braidwood, JC and NW Henry. 1990. Clinical efficacy of chlortetracycline hydrochloride administered in milk replacer to calves. Veterinary Record. 127:297−301.
  17. Schifferli, D, RL Galeazzi, J Nicolet, M Wanner. 1982. Pharmacokinetics of oxytetracycline and therapeutic implications in veal calves. Journal of Veterinary Pharmacology and Therapeutics. 5:247−57.
  18. Luthman, J, SO Jacobsson, B Bengtsson, C Korpe. 1989. Studies on the bioavailability of tetracycline chloride after oral administration to calves and pigs. Zentralblatt für Veterinärmedizin. Reihe A. 36:261−8.
  19. Palmer, GH, RJ Bywater, and A Stanton. 1983. Absorption in calves of amoxicillin, ampicillin, and oxytetracycline given in milk replacer, water, or an oral rehydration formulation. American Journal of Veterinary Research. 44:68−71.
  20. NAHMS Dairy 2007. USDA:APHIS:VS Centers for Epidemiology and Animal Health, 2150 Centre Ave, Bldg B. Fort Collins, CO 80526.