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August 2011 Archive for Dairy Today Healthline

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Dairy Today Healthline

Minimize Bovine Respiratory Disease in Replacement Heifer Calves

Aug 29, 2011

A syndrome rather than a single disease, BRD often has multiple causative factors and pathogens.

 

Bayer   Jim SearsBy Dr. Jim Sears, Veterinary Technical Services, Bayer Animal Health

Replacement heifer calves represent the future of your dairy herd. One of the significant threats to their health and productivity is BRD, or Bovine Respiratory Disease. This article will address some items to consider when BRD occurs in your calves. 

BRD is really a syndrome rather than a single disease. Most scientific journals refer to it as BRDC, or Bovine Respiratory Disease Complex, to convey that it often has multiple causative factors and pathogens. The time-honored “formula” (Stress + Viruses + Bacteria = BRD) still provides an accurate description of our overall understanding of this syndrome. After some type of stress, often complicated or initiated by a viral infection, the immune system of the calf is weakened sufficiently that a bacterial infection then takes hold in the lungs. 

Where do the bacteria come from? Basically they are present in a dormant form in nearly all normal cattle. The calf typically becomes infected immediately after birth through the process of suckling the dam. The bacteria tend to stay dormant in the calf for weeks or months and become a problem when / if the immune system becomes weakened.

There are four bacterial pathogens most often associated with BRD: Mannheimia haemolytica, Pasteurella multocida, Histophilus somni, and Mycoplasma bovis. Each of them can cause a slightly different clinical syndrome, but there are some important commonalities:

·         Once a bacterial infection takes hold, it can progress very rapidly. Calves can go from clinically normal to severely diseased or even dead within one to two days.

·         If a bacterial infection goes unchecked, it can result in permanent lung damage, even if the calf returns to apparent normal health. Mycoplasma bovis, for example, is notorious for causing mild disease initially and advancing slowly but resulting eventually in severe and permanent lung damage. 

·         The more advanced an infection is before effective therapy is initiated, the more difficult the response and the more likely permanent lung damage or even death becomes. Early detection and effective treatment is essential.  Consider these items:

  1. Evaluate calves between milk feedings. Many calves with BRD will continue to drink until the disease becomes severe.

  2. Evaluate the entire clinical appearance; not just rectal temperature. Some calves can be clinically ill but have a normal or slightly elevated rectal temperature. Routinely evaluate calves for such things as depression, cough, nasal or ocular discharge, ear droop, head tilt, head shaking, and ear scratching, to name a few.

  3. Select an antibiotic that is labeled for BRD and follow the label. An ideal antibiotic is one that quickly achieves therapeutic levels at the site of infection and achieves a rapid response. This gives you the best chance to minimize lung damage.

  4. Establish a consistent and systematic method for clinical assessment of calves before treatment and subsequent evaluation of results. A good option is the Calf Health Scoring System developed by Dr. Sheila McGuirk of the University of Wisconsin College of Veterinary Medicine. It can be viewed at www.vetmed.wisc.edu, downloaded or obtained from Bayer Animal Health in a Breathe Easy®  BRD Detection and Treatment Kit. Contact your Bayer Food Animal Sales Representative or call Bayer Animal Health at 800-633-3796 to obtain a copy to use in your operation. 

With a good plan in place and a systematic method for clinical assessments and evaluation of treatment results, you can minimize the damaging effects of BRD in your replacement heifer calves and help protect their future productivity. 

Contact Dr. Sears at jim.sears@bayer.com.

When Vaccines Fail

Aug 01, 2011

The reality is that while vaccines offer significant protection against disease, no vaccine can protect 100% of the animals 100% of the time. Here’s why.

 
thayerBy Travis Thayer, DVM, AgriLabs Technical Services
 
Vaccines are an essential tool of any animal health program. Most vaccines on the market today are efficacious and safe and, in the vast majority of cases, they provide excellent protection against disease.
 
However, in some situations, producers experience situations where animals still get disease in spite of adequate vaccination. It is natural to want to blame the vaccine, especially since, in the vast majority of cases, vaccines work extremely well, setting expectations high for producers and veterinarians. 
 
The reality is that while vaccines offer significant protection against disease, no vaccine can protect 100% of the animals 100% of the time.
 
So what could be going on when animals break with respiratory disease in spite of having received an appropriate vaccine regimen? In general, this can be attributed to one of three factors: “broken” management, “broken” animals or “broken” vaccine. If one or more of these failures occur, the herd is likely to experience a higher-than-expected level of disease.
 
Broken Animals:  This means that, for some reason, despite administration of a quality vaccine product that has been handled properly and given at an appropriate time, the animal does not respond properly to the vaccine, resulting in less-than-optimal protection and higher-than-expected respiratory disease. 
 
There are many factors that could contribute to decreasing an animal’s ability to respond to vaccines. Some of these include extreme weather, high parasite loads, less-than-optimal nutrition, or animals that are stressed by things such as weaning, shipping, etc. In some cases, animals are already infected with a viral or bacterial pathogen when they receive the vaccine. Vaccines are a great management tool, and certainly help to decrease the risk that an animal will break with respiratory disease. However, even under optimal conditions with healthy cattle, not all animals will be 100% protected, which is why revaccination is often necessary.
               
Broken Management: Sometimes conditions occur which are beyond our control. However, sometimes the way we manage animals or handle vaccine products “sets up” the vaccination program for failure. 
 
For example, receiving a load of cattle who have just been shipped for two days in the summer heat, vaccinating right after they get off the truck, and expecting optimal protection is just not realistic. Likewise, weaning, castrating, co-mingling different groups of animals, and vaccinating all at once may not be the best possible program for optimal immunity. Each of these events alone causes significant stress, and taken together, the stresses are additive and can suppress animals’ immune systems, causing some or all of the animals to respond poorly to vaccination. 
 
Another example of a place where vaccine programs do poorly is failure to follow label instructions for vaccines, especially with respect to mixing, storage and handling. Modified live vaccines (MLV) need to be mixed according to label instructions, protected from light and heat and used as soon as possible after they are mixed. A general guideline that many veterinarians recommend is to use them within an hour after they are mixed. Mix up vaccines “as you go” rather than mixing up vaccine for all the cattle that you are going to vaccinate that day. Bacterial products are particularly sensitive to temperature, and excessive cold or heat will not only reduce their effectiveness but can actually damage them, causing release of endotoxins that can make animals sick by themselves, further depressing their immune systems and making them more likely to break with respiratory disease.
 
Broken Vaccines: While it is certainly possible to see vaccine failure, due to different strains of organisms than that covered by the vaccine, less-than-optimal efficacy, etc., this in reality does not occur very often. In most cases, animal or management factors or even bad weather are more often the cause for vaccination programs that fail to protect animals as well as we expect them to. 
 
The best way to ensure that vaccination programs work properly is to review your management and vaccination protocols with your veterinarian on a regular basis, and to call your veterinarian for help if animals break with disease despite an adequate vaccination program.
 
In addition to your veterinarian, vaccine companies have technical service veterinarians who are happy to help sort out (preferably together with your regular veterinarian) what may be going on when you see higher-than-expected disease in your herd. Your veterinarian or animal health supplier can put you in touch with them to help troubleshoot the problem.
 
After obtaining a B.S. in Microbiology and a DVM Degree at UC Davis, Dr. Thayer practiced dairy production medicine in California’s Central Valley. He joined AgriLab’s technical services group in June 2005. Contact him at 510-910-3126 or tthayer@agrilabs.com.
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