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.

The prevalence of positive herds based on BTM of the four screenings varied from 83 per cent to 85 per cent. The geographical distribution of the 89 herds and their BTM status in the first and last sampling are presented in Fig 1. The results of the 89 herds sampled at all four occasions are presented in Table 1 . The majority of herds were found to be positive for antibodies against BRSV in the first and the last sampling. The negative herds were clustered in two regions in the county, with a few single negative herds outside these areas. Negative and positive herds were found in close proximity. 6.7 per cent (6 out of 89) of the herds went from antibody negative to positive, while 6.7 per cent from positive to negative (6 out of 89). 77.5 per cent (69 out of 89) were positive in both, and 9.0 per cent (8 out of 89) were negative in both the first and the last samplings. In three of the herds, all the young stock up to a certain age was negative, and all animals above that age were positive. The time of exposure was therefore presumed to be between the age of the oldest negative and the youngest positive animal. The results indicated that 9 of the 11 herds had a recent infection (<17 months ago). For two of the herds (herds 3 and 4), the results indicated that BRSV had not been in the herd for the last five to seven years. The level of antibodies detected was also lowest for these herds. The percentage of positive animals contributing to the BTM was also lowest for herds 3 and 4, but the mean PP of the positive animals was high (114 and 86, respectively).