The priority in any herd health program is a sound nutrition program. If livestock are not on a good nutrition program, parasite and disease control programs will not be optimal. Cattle that are nutritionally compromised and exposed to high bacterial, viral or parasite numbers can create the perfect health disaster.
This can be seen in a case study involving bovine viral diarrhea, BVD, a disease that can affect all phases of the cattle marketing system but that begins at the cow-calf level. Cows can become infected with the BVD virus in early pregnancy, resulting in infection of the fetus. Fetuses infected approximately 100 days in gestation often result in persistently infected calves and will consistently shed the BVD virus throughout their lifetime. If these calves are left in the herd, they will infect subsequent cows and their fetuses.
The producers took heifers to a sale in 2017, and one sale heifer, approximately 100 days bred, was returned to the ranch. The heifer then entered a herd of purchased cows that lost body condition in the winter of 2017-18. In 2018, the cows began to calve; several cows had lost pregnancies, and the remaining calf crop had extremely low weaning weights. The producer took ear notch samples from all calves testing for persistently infected BVD. A healthy 9-month-old calf whose dam was the heifer returned from the sale was persistently infected. That calf was euthanized but had exposed the entire herd to the BVD virus for nine months. The producer’s veterinarian recommended all animals receive a vaccination for BVD using a killed product. The producer elected not to give the booster as per label to reduce stress on the cattle.
In the 2018 breeding season, the herd containing 100 exposed cows resulted in a 70% pregnancy rate, but only 55% had a live calf. Twenty of the live calves were persistently infected positive, reducing the calf crop to 35%. The U.S. Department of Agriculture Agricultural Research Services confirmed all persistently infected cattle. Further testing indicated that 19 persistently infected cattle originated from one source; the heifer returned to the ranch from the sale. The one persistently infected calf that demonstrated a differing strain of BVD entered the herd as a pair; her dam was not persistently infected.
This case report demonstrates the importance of good nutrition and a herd health program tailored to the individual ranch. Conversely, cattle on a marginal nutritional program and not correctly vaccinated are prone to catastrophic disease issues. Initially, involving the Texas A&M AgriLife Extension Service county agent to aid in forage/soil testing and engaging the local large animal veterinarian in disease management could have lessened the economic loss in this herd.
– by Tom Hairgrove, Ph.D., DVM, professor, Texas A&M College of Agriculture and Life Sciences Department of Animal Science, and Texas A&M AgriLife Extension Service cattle veterinary specialist, Bryan-College Station