Case Study

Abstract

This study was conducted to determine the effect of removing cattle persistently infected (PI) with bovine viral diarrhoea virus (BVDV) on seroprevalence and prevalence of PI calves in an endemically infected beef herd in Colorado, USA. The prevalence of PI animals and the serum neutralizing (SN) titres of heifers, bulls and calves were determined for three cow-calf herds in a beef cattle ranch over a period of 2 years [date not given]. In the first year, identified PI animals were removed from the herd within 3 weeks of identification. Five PI animals of 2921 (0.171%) cattle tested were identified in the first year. One PI animal was a yearling heifer and the remaining 4 were calves. Three of the 4 PI calves identified were removed prior to the breeding season, when the calves averaged 2 months of age. One PI animal was not identified until weaning at 6 months of age, and was present in the herd during the breeding season. The percentage of animals with high SN titres (?1:512) were 20.6% (367/1784) to type I BVDV and 44.8% (799/1784) to type II BVDV. In year 2, PI calves were not identified and the percentage of calves with high SN titres to BVDV type I and type II decreased to 5.91 (58/981) and 18.04% (177/981), respectively. Removal of PI animals in the first year reduced transmission of BVDV as evidenced by a significant decrease in the prevalence of high BVDV SN titres and the absence of PI animals the following year. These findings support the use of PI animal identification and removal as an effective BVDV control strategy in beef herds.