Milk production and reproduction during a subclinical bovine herpesvirus 1 infection on a dairy farm

This study describes an outbreak of bovine herpesvirus 1 (BHV1) infections in a dairy herd with special reference to disease symptoms, reproductive performance and milk production losses. The study was carried out with a dairy herd consisting of 98 lactating animals. All animals were housed in the same freestall barn with intensive contact between all animals. An outbreak of BHV1 was induced by injecting three seropositive cows with dexamethasone. During the outbreak, no clinical signs were observed in any of the newly infected animals. At the time of infection, a significant drop in milk production was noted in animals that were initially-seronegative. The production loss was estimated at approximately 9.5 1 per infected animal during the infectious period of 14 days. None of the pregnant cows aborted because of BHV1 infection. During 50 days before BHV1 circulation, there was a significant decrease in the number of successful inseminations in both seronegative and seropositive animals. Therefore, it is doubtful that early pregnancies were terminated by BHV1 infection. The proportion of successful inseminations during the BHV1 circulation in this herd, and in the period thereafter, did not significantly differ from the baseline period.