The cost and risk of bovine viral diarrhea (BVD) was enough for Mead Farms to take unprecedented action. Earlier this year, Missouri's third-largest seedstock operation tested all its bulls for BVD prior to offering them for sale.
“BVD needs to be considered a real factor in any cattle operation — commercial or purebred,” says Kevin O'Bryan, Barnett, MO, manager of the Angus and Charolais seedstock operation.
Because BVD can be transmitted in the semen of an infected bull, herd owner Alan Mead, O'Bryan and their veterinarian, John Groves, decided it was time to get serious.
“Fortunately, all our bulls tested negative for persistent infection (PI),” O'Bryan says. “But by offering bulls tested to be BVD PI-free, our customers can be confident they're getting healthy bulls.
“It also helps remove us from liability over possible infections that might occur on a customer's place,” adds O'Bryan. “We felt is was time to begin testing — for a lot of obvious reasons.”
What bothers O'Bryan most about BVD is that it's the precursor to a wide range of respiratory diseases in young cattle. BVD is a multi-faceted disease because of viral diversity that leads to a difference in the clinical outcome of the infection. This diversity complicates control of the disease with vaccines alone.
But the challenge can be met by following strict biosecurity guidelines, eliminating PI animals, vaccinating the entire herd and providing calves with colostrum, says Bill Kvasnicka, Extension veterinarian, University of Nevada-Reno.
While Kvasnicka admits this is all easier said than done, he emphasizes the disease is usually much less severe in cattle that are well vaccinated and not heavily stressed. Often, the only visible signs are sporadic abortions and/or repeat breeding.
Strict Vaccination Schedule
O'Bryan says BVD is more of a chronic than an acute problem in beef cattle. “It'll sneak up on you and really compromise performance,” he says.
Mead Farms adheres to an intense vaccination program, vaccinating three times for BVD from birth to weaning. It begins by vaccinating calves against BVD at one month of age using a modified-live vaccine (MLV) that includes other respiratory viruses. The calves are administered the same type of MLV at two weeks pre-weaning, then boosted at weaning.
To address the PI issue, Mead Farms also vaccinates cows prior to breeding with an MLV product that includes a lepto/vibrio component.
Long term, O'Bryan thinks that, for the U.S. cattle industry to get a handle on BVD, all producers must be encouraged to have an aggressive testing and vaccination program.
“Anyone who provides genetics in the form of bulls or replacement females needs to be fully aware of this disease and its implications,” he says.
In fact, the National Association of Animal Breeders (NAAB) provides standards for the health monitoring and disease surveillance of donor bulls and teaser animals. NAAB upgraded the requirements for BVD testing in 2002.
According to NAAB, all bulls and mount animals headed for approved AI centers must be tested for persistent BVD infection with negative results before entry into the bull stud's resident herd. Furthermore, all bulls are to be evaluated by a testing program to detect persistent testicular infection (PTI). Any bull with PTI for BVD isn't eligible for semen collection and can't remain in the resident herd.
In addition, processed semen must pass a BVD virus isolation test before it's released for use.
Beyond Passive Immunity
Veterinarians generally agree that a good dose of colostrum is the first line of defense against BVD. A dam carrying BVD virus Types 1 and/or 2 antibodies will transfer temporary passive immunity to the calf through her colostrum. This protection usually lasts four to eight months.
Since it isn't possible to distinguish seropositive and seronegative calves without a blood test, all calves should be vaccinated to induce active immunity no earlier than one week of age, Kvasnicka advises.
“Vaccination will have little effect on calves with high maternal antibody from the colostrums. However, it will boost the immunity of calves with low maternal antibody and protect seronegative calves from infection,” Kvasnicka says. He notes that vaccinated cows exposed to the virus at less than 125 days of pregnancy may still occasionally produce PI calves.
While more than 160 BVD vaccines are licensed in the U.S. — most of which are produced from a Type 1 BVD virus — only a handful currently contain a Type 2 BVD virus.
“Type 1 vaccines are effective in protecting cattle against Type 1 BVD virus and may provide partial protection against some Type 2 viruses,” Kvasnicka explains. To provide a broader range of protection, he recommends using vaccines containing both the Type 1 and Type 2 BVD virus.
BVD vaccines are available as MLV or killed. Kvasnicka says the MLV is today's best bet, generally providing better cross protection against strains of BVD.
Even so, what has 40 years of vaccinations and 160 currently licensed vaccines done to eradicate a disease? Not much to this point, says Julia Ridpath, USDA-ARS microbiologist at the National Animal Disease Center, Ames, IA.
Whereas cattle diseases such as foot-and-mouth have made the headlines and are the subject of strict regulations, BVD has remained largely unfettered by governmental regulations.
“When you talk about the BVD virus, apparently not much progress has been made with this disease — it's still thriving,” Ridpath says. Around 80% of cattle in the U.S. have been exposed to BVD, about the same level as in 1960, she says, adding: “We're not making a big dent.”
Can Sentinel Animals Do The Job?
Wayne Fahsholtz, CEO of Padlock Ranch, Ranchester, WY, is one rancher who's looking under every rock to identify PI animals and track the disease in a herd.
“In our struggle with BVD, it's difficult to determine if the disease is present or presents a challenge,” he says. “Data on feed costs, treatment, etc., shows that it's very expensive to have that PI calf in the group of weaned calves.”
Fahsholtz wonders if BVD could better be managed if the calf could be traced back to the cow through individual identification.
“We're not in a position to individually identify calves at birth but maybe such technologies as DNA marking could help,” he says. “PI calves could be identified and the cow eliminated from the herd.”
But for the sprawling Padlock Ranch where thousands of cattle are divided into several herds ranging two states, tracing a calf back to its mother isn't easy. So Fahsholtz is looking at using unvaccinated sentinel animals to monitor for BVD.
He's gathering information to help build a protocol for his operation. Specifically, he's unsure how many unvaccinated steers or spayed heifers would be representative of a population — and how long they would stay in the herd.
Sentinel animals could be tested periodically, he suggests. “I don't think it would take long to know if a disease prevention strategy is working,” he says.
The downside, he knows, would be that a rancher would have to maintain unproductive animals — and unvaccinated individuals could become a reservoir for the disease.
Kvasnicka sympathizes with Fahsholtz's situation.
“BVD poses some incredibly huge hurdles for large Western cow/calf ranchers,” he says. “Most, though, can help themselves by sitting down with their animal health advisors and developing a practical herd health plan that fits their management system.”
More Than Meets The Eye
Bovine Viral Diarrhea (BVD) is a reproductive disease with immense economic consequence. It causes early embryonic loss, fetal abnormalities, abortions and the birth of persistently infected (PI) calves. If pregnant animals recover, they may abort two to four weeks after exposure, especially if they're in the second trimester of pregnancy.
Those exposed in the first trimester may experience early embryonic death, while open cattle may fail to conceive and return to heat. Some cattle, if exposed at less than 125 days of pregnancy, may not lose their fetus, but go on to deliver a PI calf.
Producers can identify PI animals with a blood test or ear notch and cull them to decrease the amount of BVD virus circulating in a herd.
The signs of BVD vary, depending on the immune status of the exposed animals, and the strain of the infecting virus, says Bill Kvasnicka, Extension veterinarian, University of Nevada-Reno. He lists several characteristics of the disease:
BVD occurs as an acute infection, but 70-90% of all BVD virus infections occur without the appearance of clinical signs. The incubation period is three to five days.
Following acute infection, most clinical outcomes are mild. Signs include fever and diarrhea followed by recovery.
If susceptible (non-vaccinated) animals are infected with a virulent strain of BVD, the disease will likely appear as an acute, severe sickness, with high fever (105-107°), off-feed, mouth ulcers and often pneumonia.
Infrequently, a chronic form of BVD (mucosal disease) occurs, usually causing death of infected animals. Occasionally, the BVD virus will cause bloody diarrhea.
Since BVD is a viral disease, antibiotics are ineffective.
Ideally, newly purchased cattle should be vaccinated before entering the herd, then isolated two to three weeks. Unvaccinated new arrivals can develop BVD virus when exposed to PI cows in the herd. Likewise, unvaccinated home herds can break with BVD if a newly purchased animal is shedding the virus. Sick animals should also be quarantined to prevent spread of infection.