Bovine viral diarrhea virus (BVDV) was first recognized in the 1940s. One of the first meetings of the Academy of Veterinary Consultants in 1972 discussed the impact BVDV had on feedlot respiratory disease. Today the discussion continues, but now is laced with terminology including immunohistochemistry, cytopathic/non-cytopathic and persistent infection (PI). In the big picture, BVDV is a minor player compared to other factors much more important in determining disease occurrence in feedlots (calf development, animal marketing, age at placement, etc.). It has been implicated in causing immunosuppression leading to increased feedlot morbidity due to bovine respiratory disease (BRD) complex. In the last several years, BVDV has been at the forefront of cattle disease discussions.
In 2001, Guy Loneragan, BVSc, PhD, West Texas A&M University, and Dan Thomson, DVM, PhD, Kansas State University, were interested in finding out BVDV’s impact on animal health and performance in the feedlot. They conducted an epidemiological study (JAVMA, 2005) that documented a ~40% increase in the incidence of disease (attributed to BRD) in cattle exposed to animals persistently infected with BVDV. However, in a follow-up study with Mississippi-origin calves, the adverse effects on health were not repeated.
Putting an economic figure on BVDV in the feedlot also proves difficult. In Thomson and Loneragan’s study, exposure to PI animals was associated with an improvement in the profit/loss outlook. “Clearly that does not make a lot of sense as there was more disease in those animals, but they also gained faster,” Loneragan says. “Some data show a clear economic detriment of exposure to PI animals, yet other data fail to detect an adverse effect on performance. The effect is not predictable and may be strain-specific.”
Thomson adds that feedlot cattle can be exposed to BVDV virus from PI animals as well as acutely infected animals. “I believe the acute infections are more from commingling and sale-barn type of environments,” says Thomson. “We have no biosecurity in feedlots.”
The identification of the Type II BVDV genotype in the 1990s caused a stir in the industry and differing opinions on cross-protection of BVDV Type 1 and Type II vaccines.
In the late 1990s testing for PI BVDV cattle, using immunohistochemistry (IHC) on an ear-notch or other piece of skin, changed everything regarding the ability to detect PI animals. “Instead of serial virus isolation, we could take one sample and be reasonably confident that we could identify PI animals within a few days,” Loneragan explains. “This enabled logistically feasible and cost-effective research so that we could at least begin to evaluate the effects of PI animals in feedlots, identify PI animals in cowherds, etc.” Since then, newer technologies or application of existing technologies have emerged, such as antigen-capture ELISA and polymerase-chain reaction. “Further, there is the potential for real-time BVDV tests in the future that could identify PI animals using complex but portable or chute-side pattern recognition algorithms,” Loneragan says.
The latest can of worms to be opened is about testing for PI BVDV cattle upon arrival at the feedlot. There’s no question identifying and managing/culling PIs at the cow-calf ranch is an important component of effective BVDV control, but there is debate over whether testing at the feedlot is beneficial. PI testing at the feedlot has led to a robust new industry in diagnostics and a profit center for feedlot owners or those offering the tests, such as veterinarians, but some question the value of it.
“Today there is not enough literature to support testing all cattle entering the feedlot,” Thomson says. “We, as veterinarians, cannot market disease. We have not answered all of the questions as to whether testing on arrival at the feedyard is warranted.”
Right now feedlots are not paying premiums for BVDV-free calves, Thomson says. “If anything, I think the feedlots are testing and relaying information back to the cow-calf producers. We are doing this backwards. We are trying to control a cow-calf disease at the feedlot level. It is too late.”
Thomson believes prior vaccination pays to prevent acute infections, and it has been shown to prevent
viremia when calves are exposed to BVD virus, but, “I think it is more important to vaccinate the cows prior to the breeding season, to prevent the PI calves to begin with.”
What does the future hold?
Loneragan believes new and better diagnostics will come along for BVDV. As far as research, he hopes we will be able to better understand why some studies show an effect of BVDV in the feedlot and others don’t. “Also, I hope that in time, research clearly demonstrates to producers that the major point of impact and most important point of control is at the cow-calf level,” he says.
“We won’t change how we buy and sell cattle,” sums Thomson. “Biosecurity is nearly non-existent in our marketing and feeding system. Customer yards are using BVDV status for marketing themselves to gain more clients. Order buyers are using it to sell more cattle. Veterinarians are using it to sell more tests and gain more clients. University guys are using it to get more research. If we vaccinated all the cows in the United States on a regular basis, this would be a non-issue in five to 10 years.”