Association between the level of antibodies in bulk tank milk and bovine respiratory syncytial virus exposure in the herd

Klem, T. B.; Tollersrud, T.; Østerås, O.; Stokstad, M.

BTM samples were collected from herds with 20 or more cow-years (the mean number of cows in a herd during one year) in Akershus County in Eastern Norway. In total, 108 herds met the criteria, representing 60 per cent of the total number of herds in this county. Three of these herds were excluded due to the use of a vaccine against BRSV, leaving a total of 105 herds to be included at the start of the study. The number of herds tested declined in the course of the sampling period due to farms shutting down and failure to take samples. Bulk tank milk from the herds was collected on four occasions: in December 2009 (n=99), February 2010 (n=99), December 2010 (n=99) and February 2011 (n=95). Eighty-nine herds were sampled on all four occasions. The herd size and number of lactating cows contributing to the BTM in each herd was registered at the first stage of sampling.