[Udder health: the influence of BVD-free status]

The effect of BVD v-free certification of BVD v-infected dairy herds on udder health was determined, by comparing parameters of udder health in 319 cases and 629 controls. Cases were dairy herds that originally had at least one BVD V antigen-positive animal but which subsequently became BVD v-free and maintained this certified status for at least 2 years. Controls had an unknown BVD V status. Each case was matched with two controls by region and herd size. The three udder health parameters were bulk-milk somatic cell count (scc), the proportion of cows with a high scc, and the proportion of cows with a high scc after previously having a normal scc (these cows were considered to have a new intramammary infection). Udder health was better in the cases in the 2 years preceding the BVD V-free period than in the controls. BVD V-free status was not associated with bulk-milk scc or the proportion of cows with a high scc but was associated with occurrence of a new intramammary infection:fewer case cows had a new intramammary infection than control cows (difference 0.6%; P < 0.05).