STOCK BVD
BVD test identifies infective calves
N
ew evidence from a New virus’s transmission across the placenta. Zealand study supports the When fetal infection occurs before the use of Bovine Viral Diarrhoea development of a fully functioning (BVD) calf ear notch testing immune system, persistently infected (PI) to detect persistent infection (PI) cattle are born. A PI calf will always in calves at any age. Identifying carry the BVD virus and will never and culling these animals, who generate antibodies specific to remain carriers of the disease the virus because its immune throughout their lives, system does not recognise minimises the spread of the the virus as “foreign” at the disease and the unnecessary time of infection. PI cattle culling of acutely infected are the leading cause of new animals. acute and fetal infections BVD is a Pestivirus that owing to their shedding of Andrew MacPherson, IDEXX Medical Affairs Veterinarian. spreads rapidly and has been enormous amounts of the found in about 80% of New virus via all body fluids. Zealand’s dairy and beef herds. Its cost to Current estimates place the prevalence NZ dairy farmers is $127 million ($70,000 of PI animals in BVD-infected herds in per average herd). New Zealand at less than two percent, and The disease causes reduced fertility, identifying and appropriately managing abortion, congenital defects, reduced milk PI animals is the primary focus of BVD production and increases susceptibility to control programmes. other infectious diseases due to immune suppression, particularly in young calves, WHY IT IS ESSENTIAL TO TEST which can lead to increased calf deaths. NEWBORN CALVES AND HOW But voluntary control is entirely achievable TO DO IT through a community effort to identify Since the effects of BVD can look similar to and remove infected animals from dairy those of other diseases, knowing the farm herds. BVD status is crucial in the fight to achieve There are three types of infection – control. Comprehensive diagnostic testing acute, fetal, and persistent. plans are fundamental to making informed A first-time exposure to the virus in decisions on controlling and preventing naïve, susceptible animals results in acutely the spread of the BVD virus. infected (known as transiently infected BVD control consists of two critical or TI) animals that recover but shed low mechanisms that, together, break the levels of the virus. within-herd transmission cycle: the early Infected dams will be at risk of identification and removal of PI animals; causing fetal infections due to the and strict herd biosecurity to prevent the
reintroduction of the BVD virus from outside sources. Detecting PI animals is, and should remain, the primary focus for farmers working to remove BVD from their properties. Previous studies have demonstrated that an enzyme-linked immunosorbent assay (ELISA) test using a small bit of ear tissue (ear notch) is an accurate, economical, and feasible way of detecting PI calves in New Zealand. A 2019 research trial by Cognosco Animal Health in New Zealand was designed to assess the sensitivity and specificity of ear notch samples of calves analysed using a specific antigen ELISA test and real-time PCR testing at four time points after birth. The trial results demonstrated an economical breakthrough, said Andrew MacPherson, IDEXX Medical Affairs Veterinarian. “We now have the perfect test to focus our efforts on identifying only PI animals, saving unnecessary culling of acute animals and enabling farmers to maximise their return on the calves born each year. ” Adopting a simple and easily understood test for every calf born is a significant opportunity for the New Zealand dairy industry to control BVD voluntarily. Farmers’ willingness to test all calves to identify PI animals and remove them from their farms, combined with improved biosecurity, will deliver economic benefits for all farmers and lead to significant improvements in New Zealand’s BVD status.
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