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VACCINATING CALVES FOR OPTIMUM IMMUNITY

Recent work shows that early calf vaccination can create an immune response. This flies in the face of what we have long assumed, and it gives producers opportunities to protect calves from disease.

For decades, veterinarians have been taught that young animals cannot be vaccinated as long as there are maternal antibodies circulating in the bloodstream. Vaccination schedules have been designed so that vaccines are given when maternal antibodies have disappeared. The alternative is giving multiple doses of vaccine to catch the window of time when maternal antibodies wane.

However, investigators have found that young animals vaccinated in the face of maternal antibodies (IFOMA) can react to the vaccine and they can be protected from disease. But, there are still limitations. Vaccination IFOMA is not always successful in creating immunity to later disease challenge, but by planning your vaccination strategy, it is possible to optimize the immune response.

The response to vaccination in the presence of maternal antibodies is evaluated two different ways. One way is to vaccinate calves and look for an increase in antibodies circulating in the serum. The other method is to vaccinate calves and then expose them to the real disease months later. This latter type of test is much more meaningful, but it is also expensive to carry out.

The commonly held understanding that vaccination IFOMA cannot stimulate an immune response came from animals not displaying an increase in serum antibodies two to four weeks after vaccination (this is described as failing to seroconvert). The standard measure of activation of the immune system is a four-fold or greater increase in the titer (amount) of antibody in the blood to a specifiinfectious agent.

A lack of seroconversion was presumed to mean that the immune system was not stimulated by vaccination. However, some researchers recognized that these calves were capable of generating a high level of antibodies with a subsequent vaccine booster. This implies an anamnestic (memory) response suggesting that the immune system was previously stimulated.

For example, calves given a modifi ed live virus (MLV) vaccine containing Infectious Bovine Rhinotracheitis (IBR) between two and three months of age failed to produce an antibody response. However, at seven months of age when they received a second dose, they produced a high level of antibody consistent with a memory response. In contrast, calves vaccinated just once at the later time produced antibody levels significantly lower than those vaccinated earlier in life.

There is also a difference in response to various vaccines. Calves in one study were vaccinated at an early age with three different brands of killed vaccines. Each one contained IBR, BVD (Bovine Viral Diarrhea) types 1 and 2, as well as PI3 (Parainfluenza type 3). One of the products proved that it could stimulate a persistently elevated level of antibodies while the other two did not. This shows that the formulation of the vaccine and/or the adjuvant (an additive that boosts immune response) it contains may be important in stimulating a reaction IFOMA.

In field studies of very young calves vaccinated against m. haemolytica and Haemophilus somnus, the effect of just one injection versus two was examined. Calves that received vaccines at three and four months had significantly higher titers to both bacteria than nonvaccinated herdmates. Calves that had one vaccine at four months of age had lower levels of antibodies. Two doses of vaccines seem important.

The summary from this research is

S/B Guidelines for Vaccinating Calves

1. Vaccination as young as one month of age can protect calves against viral respiratory disease. Modified live vaccines are the ones used most often in these studies.

2. A single dose may be sufficient, but two doses at a two-to four-week interval are superior.

3. Vaccinating under one month of age is not as reliable.

4. Antibody titers will not usually increase with vaccination IFOMA and they can’t be used to determine vaccine effectiveness.

5. If calves have incomplete or complete failure of passive transfer, a single dose of MLV vaccine can be safe and efficacious at a very early age.

6. Though most studies show the value of MLV vaccines, there are some killed vaccines that are efficacious. The success of a killed product depends on its formulation. Results from one study on one vaccine brand can’t be extrapolated to other vaccine brands.

that vaccines administered IFOMA can induce a measurable immune response.

A more relevant question is whether or not calves vaccinated IFOMA are protected from disease when maternal antibodies have waned and are no longer present. Calves must be exposed to the disease to observe this response.

In one experiment, calves vaccinated at three weeks of age (when maternal antibodies are certain to be present) with an intranasal modified live BRSV (Bovine Respiratory Syncytial Virus) vaccine were protected against challenge at three months of age. The calves did not have clinical signs and did not shed the virus after challenge.

In the same study, calves given a killed intranasal BRSV vaccine or a modified live BRSV intramuscularly and similarly challenged again did not have symptoms but did shed the virus. Their protection was not as complete. This means that the route of vaccination as well as the type of vaccine has an impact.

A very informative study was done on calves given the BVD type 1 vaccine. There were four groups. One group received colostrum containing high levels of BVD antibodies and were vaccinated at 10 to 14 days of age. A second group did not receive colostral antibodies against BVD and were vaccinated at the same time.

A third group did not receive antibodies, but they were not vaccinated. A final group did not receive antibodies but were vaccinated at four months of age.

At 4.5 months of age, all of the study calves were exposed to BVD type 2. All four groups of calves developed some signs of BVD disease. The calves vaccinated at four months of age, as well as the calves with no colostral antibodies and vaccinated at 10 to 14 days, developed just mild symptoms. In contrast, the calves that were never vaccinated and those that were vaccinated at 10 to 14 days old IFOMA developed severe disease. In fact, most of the calves had to be euthanized.

This study shows that calves vaccinated at two weeks of age IFOMA are not protected against severe disease when challenged. Were they too young? Or did the maternal antibodies interfere? Because the young calves that lacked maternal (colostral) antibodies were effectively vaccinated against BVD, it seems that the colostral antibodies are the problem. There is interference with maternal antibodies at this young age and vaccinating later makes sense.

This last study was done in controlled circumstances with a disease that was introduced to the herd. Actual field trials to determine vaccine effectiveness rely on the disease occurring naturally during the observation period. This is why there is a paucity of published field trials. However, it has been done.

A beef herd that had an unusually high incidence of pneumonia in nursing calves became a field trial demonstrating the benefit of calfhood vaccination. Calves were vaccinated at three and five weeks of age with a MLV BRSV vaccine as well as a M. haemolytica/H. Somnus vaccine, or they were given no vaccines at all. Only 15 per cent of vaccinated calves needed treatment. In contrast, 34 per cent of unvaccinated calves needed help.

Dr. Amelia Woolums from the veterinary college at the University of Georgia reviewed the literature and came up with suggestions on vaccinating calves (see sidebar).

Current research shows that calves can be vaccinated IFOMA even if the response can’t be measured. It can protect nursing and post-weaning calves when there is a reasonably high risk of disease.

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