By now most cow-calf producers are aware of bovine viral diarrhea 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 sickly calves. Others have seen the impacts of BVD further down the production chain, with high morbidity and mortality rates among stocker or feedyard cattle.
And with effective tests, vaccines and management tactics available to control BVD, it seems intuitive that producers should do everything they can to stop it in its tracks. But it's not that simple because control measures must make economic sense for an individual operation, and the economics depend largely on risk levels. For one operation, doing everything possible could be too much, with costs far exceeding benefits. For another operation, doing a little might be the same as doing nothing, with costly results.
Dan Givens, DVM, PhD, who serves on the faculty at Auburn University, has conducted research on BVD and worked with producers on practical control strategies. He says the first step for producers is to take a close look at their operations, evaluating their risk factors and trends that might suggest presence of the disease.
Monitor cow fertility, conception rates, abortions and calving rates, he says. Are any of these headed in the wrong direction? Also look at calf health from birth to weaning. Is there a high rate of birth defects or respiratory disease in calves?
If a producer does not see any of these negative reproductive or calf-health trends, Givens says he would not recommend widespread BVD testing in the herd. "You can't say for sure the virus isn't there," he says, but there is no economic justification for broad testing without some evidence of disease. Instead, he recommends a two-pronged approach focused on biosecurity and monitoring.
Test breeding animals entering the herd from outside the operation, and test calves from imported pregnant females.
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 could suggest BVD, such as an aborted fetus, 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.
In a situation where a producer does see signs that could suggest BVD in the herd low pregnancy rates in well-conditioned cattle, birth defects or sick calves more extensive testing becomes necessary. Givens suggests several possible testing strategies.
Screen all animals in the herd for persistent infections with BVD.
For a lower-cost option, limit testing to high-risk animals such as sick calves or aborted fetuses to determine if BVD is present.
Another option, if the operation has calves older than seven months that have not been vaccinated for BVD, is to test those calves for antibodies to the virus. If they are positive for antibodies, the BVD virus is circulating on the farm and further control measures are necessary.
Bill Rishel, of Rishel Angus, North Platte, Neb., likes to keep things simple, while also recognizing the importance of keeping BVD out of his purebred herd and those of his seedstock customers. He applies biosecurity measures and monitoring for signs of disease, and stresses the importance of a good, all-around animal-health protocol including vaccination against BVD.
Commercial producers, he says, should purchase bulls from breeders who test for BVD and know their animals are PI-free before putting them on the market. "This won't prevent their herd from being exposed from neighbors" cattle across the fence," he says, but it's a good start on biosecurity.
Rishel quarantines and tests all imported animals before introducing them to his herd, and tests all bulls before sale and calves born to any imported females. He vaccinates heifers prior to weaning and before breeding with a modified-live BVD vaccine. He also closely monitors indicators such as pregnancy rates, weaning percentage or calf performance, and will vaccinate cows prior to breeding and increase testing if ranch records indicate any problems.
One concern, Rishel says, is the risk of exposure from growing wildlife populations in many cattle-production areas. He believes the industry should make it a priority to work with state and federal wildlife agencies to manage populations of wildlife, particularly ruminants such as deer and elk, to reduce the spread of BVD and other diseases including brucellosis and tuberculosis.
Time to test
Producers who decide to screen their herds can choose between individual tests, which naturally come at a higher price, or pooled samples, which determine whether any animals in a group carry the virus but don't identify the culprits. Pooled samples, when negative for the virus, can cost-effectively confirm that large groups are free of the disease. The challenge comes when a pooled sample comes up positive.
The goal of this testing, Givens says, is to identify persistently infected cattle. These PI calves are infected when their dam is exposed to the virus during the first 125 days of gestation and are born carrying the BVD virus. They will shed the virus and spread the disease as long as they live, which in some cases can be well into maturity.
If the test on a pooled sample is positive, the next step is to use individual testing to identify the PI animal or animals that caused it. For this reason, Givens warns about pooling too many animals into one sample. One test for 200 cattle initially costs less than four samples from groups of 50 cattle, but in the case of a positive result, smaller groups mean less individual follow-up testing.
The PI dilemma
Finding a PI animal and isolating it can prevent tremendous disease-related losses at the cow-calf, stocker and feedyard stages, but for many producers, the challenge becomes what to do with that animal.
Putting it into the market without full disclosure of its disease status is clearly unethical, as it will expose other animals as it moves through the marketing system and into other herds. But Givens acknowledges that a cow-calf producer with a PI calf faces some tough decisions. Even if identified at birth, the producer already has nine months invested in the calf. Nevertheless, for the cow-calf producer, the best option usually is to euthanize the PI animal. In some cases, people have grown them to finishing weights in isolation, or sold PI calves to other producers with quarantined facilities. But these options usually are not economically viable as most will perform poorly and many will die before reaching market weights.
Givens says he and other veterinarians talk through these issues with producers before beginning a testing program in their herds. It's important for owners to decide ahead of time what they will do if they find PI animals. If someone is unwilling to act on the results, he says, there is little point in paying for the tests.
BVD tools and online resources
The NCBA's BVD Working Group, in cooperation with the Academy of Veterinary Consultants and Kansas State University, host the BVDinfo.org web site, 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.
Recognizing that economics and logistics impose practical limits on the scope of each operation's BVD-control strategies, this tool helps producers determine their level of risk and make cost-effective control decisions that make sense for their specific environments and management systems.
The model allows producers to fill in information about their operations, such as length of calving season, types of cattle imported into the operation and neighboring herds. The tool then calculates the operation's risk level, helping the user make informed decisions on management changes and other control measures.
Based upon the risk level and factors contributing to that risk, the tool breaks down the economic effects of a list of biosecurity, testing and vaccination tactics, accounting for the cost of the management change along with its likely impact on the disease.
The BVDInfo.org site also features an article titled "Integrated BVD control programs for beef operations," authored by veterinarians Daniel Grooms at Michigan State University, Daniel Givens at Auburn, Sanderson and Brad White at K-State, Dale Grotelueschen with Pfizer Animal Health and David Smith at the University of Nebraska.
The article includes a set of tables that walk the reader through a series of options, first for determining whether BVD is present in a herd, with options ranging from lowest cost and least reliable to more reliable but higher-cost methods. Subsequent tables outline biosecurity options to keep BVD out of a herd where it is not evident and biocontainment options for herds where the previous step determined the disease is circulating in the herd. Again, the options are listed in order of their reliability and associated costs. The article also includes tables listing a range of vaccination strategies for calves, heifers and cows, ranked from least reliable to most reliable.
Givens says these tables, used in tandem with the Risk Analysis Model, can serve as a good starting point for producers and veterinarians planning BVD-control programs for individual operations.