Risk of BVD virus in ETand semen
BULLS which test negative for BVD may transmit the disease to cows via semen which contains the virus. There may also be a risk of transmitting the disease via embryo transfer, according to research results presented at the Nottingham Fertility Conference.
"Bulls at a New Zealand progeny testing centre were blood tested for BVD. No virus was found in the blood, however, semen collected from some bulls was infected," said Martin Fray, researcher at the Institute for Animal Health.
"I believe this occurs around the time of puberty when a blood-testes barrier forms, leaving virus trapped in the testes. Virus in the blood is mopped up by antibodies, so none is detected when tests are carried out."
Producers concerned about the risk of transmitting BVD to cows via semen should ask AI centres to test semen for BVD, advised Dr Fray. "A couple of straws from each bull should be checked for BVD to make sure they are clear. I believe most AI centres do this."
But it is not only semen that may pose an infection risk. Embryos destined for embryo transfer could also harbour the disease, warned Dr Fray. "The embryo transfer industry relies on washing embryos to sanitise them.
"Recently, BVD virus has been isolated from the embryo coating, suggesting that current washing procedures may not be enough to guarantee that all embryos are free from the virus.
"There may need to be more checking of cultures used to grow embryos and cows used for flushing, to ensure that embryos are free from the virus."