Most cow-calf producers are aware of bovine viral diarrhea (BVD) and the dangers it presents to beef cattle. Some have experienced it first hand, seeing the economic toll of declining conception rates, frequent abortions or unthrifty calves. Others have seen the impacts of BVD further down the production chain, with sick and poor-doing calves moving into feedlots or dealing with BVD as part of fatal and unresponsive respiratory disease.
Calving season is an opportune time to be watching for telltale signs of BVD and begin the planning process to implement control measures. There are accurate tests, effective vaccines and management tactics available to control BVD. While it might seem intuitive to wage war on BVD using all the tools at hand, control measures must make economic sense for individual producers and the economics depend largely on risk levels. Doing everything possible for one producer could be too much, with costs far exceeding benefi ts. For another operation, doing a little might be the same as doing nothing, with costly results.
The first step for producers is to take a close look at their operations. Working with a veterinarian will help evaluate risk factors and identify trends that might suggest presence of BVD.
1. How did it get here?
The presence of BVD probably means active infection exists in the herd or the virus walked on to the ranch with things like persistently infected replacement heifers, perhaps with a bargain-basement calf picked up at the local auction market or in a group of Corriente roping steers from a local stock contractor.
2. What are some of the signs BVD might be present?
Poor cow fertility, lower conception rates, abortions and reduced calving rates can all be part of the picture. BVD can affect calf health from birth to weaning. Birth defects and respiratory disease in calves are common with BVD challenge. Cows exposed to BVD during the first 125 days of pregnancy will often give birth to persistently infected calves that are unthrifty and a constant source of virus for other cattle in the herd.
3. Where does a producer start with control?
A proper diagnosis is first and foremost. The aborted fetus and dead calves show typical lesions associated with BVD that can be readily identified in a diagnostic lab. Tissue from post-mortem specimens is a rich source of BVD virus for isolation and characterization. The IHC test on skin biopsies will accurately detect persistently affected animals. Testing can start with breeding animals purchased as replacements from outside the herd and calves from imported pregnant females. Calves older than seven months, not vaccinated for BVD, can be blood tested for antibodies to BVD virus. The presence of antibodies in non-vaccinated calves means the BVD virus is circulating on the farm and further control measures are necessary.
4. Limiting risk through biosecurity
Quarantine imported animals for at least 21 days before mingling them with the rest of the herd.
Continue monitoring reproduction and calf health for signs of the disease. Work with your veterinarian to sample and test selected animals if problems appear that might suggest BVD: things like abortions, underweight calves, calves born with physical abnormalities or calves with respiratory disease. Vaccinate heifers against BVD, whether home raised or purchased, using two doses of a modified-live vaccine. Only purchase bulls and replacement heifers from suppliers who have BVD control programs in place and know animals are PI free before putting them on the market. Closely monitor other performance indicators like pregnancy rates, weaning percentages and calf performance.
5. Coming to grips with the PI dilemma
Finding a PI animal and isolating it can prevent tremendous disease-related losses at every level of beef production. The challenge becomes what to do with persistently infected animals of any age.
Selling PIs into the market without full disclosure is clearly unethical, as they shed huge amounts of virus and will expose other animals as it moves through the marketing system and into other herds. If identified as a nursing calf, the best option is euthanasia.
6. BVD tools and online resourcesThe NCBA’s BVD Working Group, in co-operation with the U.S. Academy of Veterinary Consultants and Kansas State University, host the BVDinfo.org website, which contains a wealth of information, tools and resources for controlling the disease. One practical and valuable tool on the site is an online Cow-Calf BVD Risk Analysis Model, developed by K-State veterinarian Mike Sanderson.