Last month we reviewed the BVD virus, its clinical symptoms and its devastating effects on productivity. This month we will assess the risk to your herd, diagnosing this disease, setting goals to control the disease and choosing the right tools to meet these goals.
BVDV-is this virus circulating in my herd? To answer this question, a producer must be aware of what is going on within his herd and keep accurate records to determine if his/her cattle are at a high or low risk of infection. Ask yourself this series of questions:
1. Does my herd have poor reproductive performance despite good nutrition (and fertile bulls if AI is not practiced)?
a. Is there a decrease in overall pregnancy rate and % pregnant after the first service?
b. Are there more abortions, stillbirths, and neonatal deaths than usual?
c. Are cows returning to heat more often than expected?
2. Do I see any physical abnormalities in the calves at birth such as weakness, inability to stand and nurse, eye defects, or cleft palate?
3. Does my herd have unexplained calf loss due to pneumonia or scours?
4. Do I introduce new cattle (including bulls) into the herd without testing for BVD?
5. Do animals from the neighbor’s herd come in contact (fence line) with my milking herd?
6. Is there a significant population of wild animals (such as deer) on my farm?
If you answered ―yes‖ to any of these questions, your herd is at risk for BVD (the more ―yes‖ answers, the higher the risk). Your goal should be to know with certainty if the virus is in your herd and, if found, work to eliminate it. If you answered ―no‖ to all of the questions, your herd is at low risk for BVD so your goal is to keep the herd free of the virus and minimize losses if it is introduced. In either case, the tools of diagnostic testing, vaccination, and biosecurity will all be needed to accomplish your individual herd goals.
Diagnostic testing for BVDV is important for two distinct reasons. The first reason is to find out if the virus is causing a clinical disease problem in your herd. Sending any aborted fetus and membranes, stillbirths and/or dead calves to a diagnostic laboratory will help to confirm the presence of the virus. The second, and perhaps most important reason to test, is to identify any persistently infected (PI) cattle in order to remove or isolate them before they spread the virus and infect other cattle. Recall from last month’s article that PI calves result when a cow is infected with the BVD virus between 42-125 days of gestation or if a PI cow has a calf. Once the calf is born, it is a virtual virus factory, churning out millions of virus particles in all of its body secretions throughout its life. Although many PI calves die at a young age, a small percentage will survive and look clinically normal. Therefore, it is crucial to get these PI animals away from any cows in the first trimester of pregnancy and stop the disease spread. The most commonly used sample for identifying PI cattle is skin, usually taken as an ear notch. Blood (serum) can also be used but not in young stock (calves less than 3 months old). If you suspect BVD virus is in your herd and you want to initiate testing, remember to: