Given what we know about the bovine viral diarrhea virus (BVDV) and how it spreads, the industry could reduce its incidence dramatically or even eradicate the disease. In practice, however, control of BVDV at the ranch, local or regional levels will be more feasible and likely than widespread eradication.
Recently, Julia Ridpath, PhD, at the USDA’s National Animal Disease Center (NADC) in Ames, Iowa, presented a webinar on BVDV control, which was hosted by the American Association of Extension Veterinarians (AAEV). Part 1 of this series summarized Ridpath’s discussion of diagnosis, vaccination and biosecurity as the critical components of BVDV control. This installment outlines her coverage of BVDV control points and testing, disposition of PI calves and opportunities for regional or national programs for control of BVDV.
BVDV control points
The cow-calf production stage represents the beef industry’s best opportunity for control of BVDV, through vaccination and, especially, identification and removal of PI calves. Any imported cattle should be tested to prevent introduction of BVDV, and all calves should be tested for PI status to prevent ongoing exposure. Ranchers should test the dams of any calf that tests positive for BVDV, and any cow or heifer that does not deliver a calf. Ridpath also encourages producers to isolate any “visitor” cattle, such as 4-H or FFA show calves they might house on a temporary basis.
Bull- and heifer-raising facilities should have control and testing procedures in place. In the dairy industry particularly, heifer facilities comingle cattle from multiple sources, raising the risk of importing a PI calf and exposing heifers prior to their shipment back to dairies. Dairies should test all imported females for BVDV PI status.
While feedlot testing and vaccination against BVDV can reduce morbidity losses at the pen level, the finishing stage is not an effective control point for reducing BVDV incidence overall. Control needs to occur at the cow-calf level to keep PI calves from ever reaching feedlots.
Disposition of PI calves
Scientists and veterinarians recognize that removal and isolation of PI calves is critical for control of BVDV, but that discussion always leads to the question of what to do with those calves. Producers facing tight margins might be reluctant to euthanize or slaughter PI calves that appear healthy, and the potential loss of revenue can even discourage some producers from testing.
Ethically, the options for producers who find PI calves include euthanasia or shipping directly to slaughter. In some cases, producers can limit their losses by isolating and feeding PI calves to slaughter weights, either on their own operations or at a finishing facility that is equipped to feed the animals in complete isolation from other cattle. The option entails considerable risk as morbidity and mortality rates tend to be high in groups of PI calves.
Legally, policies vary between states, but producers who market PI calves without clearly identifying their health status could be held liable when those calves spread the virus in the next production stage, such as in a heifer-raising facility.
PI case study
Ridpath outlines a case study from South Dakota State University, involving 136 bred heifers purchased as part of a herd expansion. Among their calves, 44 tested positive for BVDV-PI, while 76 tested negative. Eight of the heifers lost their pregnancies and another eight calves died prior to testing, during the first month after birth. Further testing determined that none of the dams were persistently infected.
Among the 44 PI calves identified, 12% died during the neonatal period, 5% were euthanized due to poor condition, 41% died from mucosal disease, 15% experienced sudden death without apparent lesions and 27% were successfully raised to slaughter weights.
That experience illustrates the high risk in trying to raise PI calves to slaughter weights, but also shows why producers sometimes are reluctant to test, or act on test results, when a significant percentage of PI calves appear normal.
Ridpath says the USDA has not indicated enthusiasm for implementing a national BVDV-control program, but regional efforts focused on education, management and testing could help reduce the impact of the disease. Kentucky, for example, has developed a two-tiered verification program that allows participants to document their BVDV-control programs and potentially market their calves as BVDV-free.
These programs face challenges in generating producer participation, largely because producers do not recognize the disease, or its costs, in their herds. They don’t necessarily see the losses associated with immunosuppression or lower reproductive rates, or associate those problems with BVDV. In other cases, producers resist testing because of the perceived cost of removing any PI calves they find.
In the Kentucky program, participants sign an agreement to dispose of PI calves, whether that involves euthanasia or marketing them transparently through approved channels. The program includes indemnity payments, through which producers can receive 100% of the value of PI calves euthanized at under 225 pounds, 755 if euthanized at over 250 pounds and 50% of their value if sold to slaughter or to a feedyard approved for finishing PI calves in isolation.
Ridpath reminds veterinarians they can use the BVD Consult website to help clients develop cost-effective control strategies based on their management systems and risk levels.
She also points out the 7th U.S. BVDV Symposium, hosted by the Conference of Research Workers in Animal Diseases, will take place in Chicago on December 6 and 7. Click here for more information, including registration.