Step up your methods to help eradicate BVD from the herd
Published 23/03/2010 | 05:00
Bovine Viral Diarrhoea (BVD) is a complicated viral disease and is widespread in the cattle population in Ireland.
After infection, the virus targets a wide range of sites in the body, mainly rapidly dividing tissues such as lymphoid tissues, the mucosa of the intestines, sperm-producing cells in the testes and embryonic and foetal tissues. This results in a range of clinical effects and a complex set of diagnostic tests and control measures.
Animal Health Ireland (AHI) has, in turn, targeted the disease for control and eventual eradication, as has been achieved in Scandinavian countries. AHI recently published a BVD information leaflet, which sets out a step-by-step procedure for controlling the disease. This is available on the AHI website, www.animalhealthireland.ie.
The eradication of BVD would have a major economic benefit for the beef and dairy sectors. BVD seriously suppresses the immune system and, especially in animals of low-immunity status or in young calves where the immune system has not fully developed, the severity of other diseases, such as pneumonia and scours, is intensified by BVD infection.
The main manifestation of BVD is in breeding herds, where it causes a range of fertility losses, such as repeat breeding arising from embryo and foetal loss, the birth of mummified, deformed or dead calves and the production of persistently infected (PI) calves.
These PI animals, as the name implies, remain infected with BVD all their lives, continue to shed the virus and are a source of constant infection while in the herd. The calves appear normal up to weaning as they have the protection of the maternal antibodies. From eight to 18 months of age many develop signs of ill-thrift, a persistent scour and sores on the mouth and feet. Once a PI is discovered it should be slaughtered as apart from spreading infection, it will eventually die. Some, however, grow normally and may go undetected. These are the ones that need to be identified and slaughtered -- a PI cow will always produce a PI calf.
If a cow gets infected in the early stages of pregnancy, up to about 70 days, it will usually lose the embryo and repeat. It is then likely to have developed sufficient immunity and will breed normally, but will have slipped back in calving date. If the infection occurs from about 70 to 120 days of pregnancy, the virus will get into the foetus and, at this stage, the foetus is not capable of developing its immunity as it doesn't recognise it as a foreign body, accepting it as part of its own tissue.