OUT IN THE FIELD
Balancing Immunity and Fertility in Beef Herds By Lee Jones, DVM, MC, UGA College of Veterinary Medicine
F
or cow-calf producers, fertility is the highest priority for their herds. Of course, weaning a healthy calf is required for reproductive efficiency, too. It doesn’t matter when a cow loses her calf—if she doesn’t wean a live calf, reproduction didn’t happen and there’s nothing to sell. And while fertility is the top priority for cattle owners, for the cow, fertility is a luxury that only comes after all other metabolic needs are met. That’s why when veterinarians make herd health recommendations, optimizing fertility is a high priority. However, these recommendations must also consider ranch and season prevention of infectious disease through biosecurity and disease prevention. One part of a disease prevention program is the use of vaccines to stimulate immunity or disease resistance for individual cows, as well as the herd. Vaccines protect fertility of the cow herd, enhance colostrum quality by increasing immunoglobin G levels in the cow and colostrum and increase resistance in calves to calfhood diseases. Vaccine selection and timing in the cow herd can help determine what vaccines are used in calves. How producers market calves is an important consideration when designing a vaccination program. While vaccines are important, nutrition and biosecurity are the first two lines of defense in a prevention program. Vaccines are used to increase resistance to common diseases in cow herds. They do this by stimulating the adaptive or acquired immune system which includes the cell mediated immune system (cells like T lymphocytes) and the humoral immune system that makes antibodies. Vaccines train the acquired immune system to quickly recognize the disease agents and eliminate them before severe disease occurs. The innate or natural immune system is required to activate the adaptive system. The innate immune system is dependent on adequate nutrition for it to function well. It’s important to understand that vaccines will not work in immunocompromised animals. That includes animals that are sick, parasitized or malnourished. Vaccines only work in healthy animals. In short, the animal makes the vaccine work. Not all animals respond equally to vaccines. In fact, for some yet unknown reason even some healthy looking
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animals don’t respond to vaccines every time. Studies have shown that in some cases as few as half of the animals might respond. It is important to follow the label directions when giving vaccines. There are three important factors in vaccine efficacy—the vaccines, animals receiving and humans giving them. Vaccines have to be stored, transported, handled and administered correctly. Not all vaccines work the same, so responses will likely be different in each animal and on each farm. Vaccines have antigens (things that stimulate the immune response ) and adjuvants (things that make the response better). Proper handling and administration are essential. Producers are reminded to use the right equipment and follow label recommendation and adhere to Beef Quality Assurance principles for the best response to their vaccination programs. Nutrition plays a key role in vaccine response and immunity in cattle and all living things. Researchers at University of Georgia (UGA) saw a large vaccine response difference in calves supplemented with a trace mineral injection versus those that didn’t get it. This tells us that calves need to be on a good mineral program as well to make sure vaccines achieve their purpose. Even in humans, serum mineral levels have been shown to effect response to the fly vaccine. Stress also affects vaccine response. In another study from UGA researchers, calves that went through a sale barn had a lower immune response to vaccines than calves that were weaned on a farm. Ranchers are advised to use low stress handling principles and update facilities to reduce stress in cattle when giving vaccines or completing other herd health procedures. If animals don’t respond to vaccines, they remain naïve and susceptible to disease exposure and a source of transmission to other animals, so managing cattle to ensure optimum response is critical. Viral vaccines come in two types: killed viral (KV) and modified live virus (MLV). MLV typically produce a faster, stronger, longer and more vigorous immune response in a single dose than a KV. KV vaccines require a first dose followed weeks later by a booster dose to “remind” the immune system. The second dose is called the anamnestic
