How do you fight and prevent BVD in cattle?

Answer 1

BVDV (bovine viral diarrhea virus) is a highly contagious endemic virus found throughout the United States and Canada. Most infected herds are managed via vaccination and testing for persistently infected carriers that will shed the virus and continue the infection.

If you find any cows that are testing positive for BVD, ship them out. PI (Persistently infected) cattle will always be infected and be carriers, no matter what you try to do to "fix" them. No vaccine for BVD will help fix PI calves either. PI cattle are created before birth, when the dam encounters BVD virus between 40 and 125 days of gestation. PI cattle always remain so. Those cattle that are not PI and have tested negative for BVD won't need to be tested again, not especially if you keep a good vaccination program that includes having the dams vaccinated for BVD (and other illnesses) prior to birth. So the key to eliminating PI animals is to protect your cows from BVD during pregnancy so that no fetuses will become exposed.

Cattle can be tested, and if the BVD virus is present it can often be isolated from a blood sample or tissues taken from an aborted fetus or an infected, weak or unthrifty calf. You might want to test your cows too to confirm you suspicions of why she aborted or dropped a weak or abnormal calf. Most testing programs screen for any PI calves in the new calf crop before the cows are set to breed in the next breeding season; infected calves can spread the virus to a bred cow. If any PI calves are found, then the dams have to (or can be) tested as well.

Any animal that tests positive should be checked again in 4 weeks to see if had an acute infection or is PI. The virus level will be dropping by the second test if the animal had an acute infection, but it will remain high if the animal is persistently infected. Cull ALL PI animals: cows, calves, bulls, heifers, etc.

In the first year the herd is tested, all calves, heifers, bulls, and any cows that may have lost a calf should be tested prior to breeding season. If tissue samples are taken from suckling calves before cows are rebred, you can then test the dam of any calf that tests positive. You will have to have necropsies done on any calves that are stillborn or die of pneumonia, scours or any other cause and aborted fetuses so that you can determine which cow has BVD. If the calf tests negative, there's no need to test the dam. All PI calves and their dams must be removed from the herd before they come in contact with any pregnant animals. This eliminates the risk of passing the virus on to the fetus. If you keep BVD from reaching a fetus, no more PI calves will be produced. In subsequent years, you will only need to test the young calves and any newly purchased animals. You only need to test once: if he's PI negative he will never become PI. Don't purchase any new animals unless they test negative for BVD.

The best protection against BVD is to eliminate all sources of infection within the herd, keep up a regular vaccination program using modified live-virus vaccine ahead of breeding or an oil-based killed-virus vaccine (so that cows have the strongest possible infection during early pregnancy), and NEVER let cattle become exposed to infected animals. This means that you will have to be careful about breeding cows to PI bulls or bulls that have been acutely affected with BVD, either naturally or even through artificial insemination. Even rectal palpation, without switching gloves for every cow that is being preg-checked, can transfer BVD virus from cow to cow. So a new glove for every cow is important if you want to prevent your cow herd from getting hit with a serious case of BVD. Some producers opt to do the blood test instead of the traditional rectal palpation because it's safer and has zero risk of spreading the disease from animal to animal.

Prevention:

Any animals that are coming to your herd (even home-raised heifers) need to be tested to see if they are PI and isolated from the breeding herd until you receive the test results. Only after you receive the test results can you determine whether you can cull them or add them to the herd. Often the main way the BVD virus is introduced to the farm or ranch is by the introduction of new non-tested animals to your herd. Don't bring in extra calves to graft onto cows that have lost their calves, nor purchase bulls, cows, heifers or pairs without having them tested. Introducing new animals always carries a risk of BVD transmission to susceptible animals. PI cattle can be hard to recognize because they rarely show visible signs but are continually shedding the virus and infecting other animals.

Any cow or heifer that has conceived a calf somewhere else, be it bred on the range or communal pasture or purchased as bred, should be isolated until her calf is born and tested. Purchased pregnant animals can be PI negative themselves and still carry a PI-positive fetus that was infected during pregnancy--the dam may have recovered from an infection and test negative, but once the calf is born, he can expose your animals to BVD.

Avoid communal pastures or fenceline contact with other cattle, especially during that time when your cows are in early to mid gestation. And finally, make sure all females are adequately vaccinated to provide a high level of protection in case the do become exposed to BVD during their pregnancy.

As far as vaccines are concerned, you should talk to your vet about that. There's some risk of using MLV vaccines to bred cows, since it could be too potent and affect the fetus inside her, render her temporarily sterile for a few months, or cause embryo death if given too late after breeding. MLV's tend to have a stronger and longer lasting immunity than aluminum-hydroxide based killed vaccines or other killed vaccines that are not oil-based. However, oil-based killed vaccines tend to give excellent results, and produce better vaccine titers than either MLV or any other killed vacccines. They are slower to absorb, safer than MLV vaccine, and gives the animal time to build a strong immunity.

But as far as a herd health vaccination program with your herd, it's strongly advised to discuss this with your veterinarian. Together you can determine when cows should be vaccinated and when and how often your calves will need to be vaccinated as well.