EVIDENCE FOR TRANSMISSION OF BOVINE LEUKEMIA-VIRUS BY RECTAL PALPATION IN A COMMERCIAL DAIRY-HERD

The risk of Bovine Leukemia Virus (BLV) transmission by rectal examina tion was determined over 22 months in a commercial dairy herd. All 167 BLV seronegative cattle, of breeding age or greater, were divided ran domly into two groups and identified by neck-chain color. In the treat ment group, routine rectal palpation occurred after a BLV infected ani mal and without a change of sleeve, while in the other group, palpatio n occurred in a similar manner with the exception that sleeves were ch anged between animals. When BLV seronegative cattle in either group we re palpated after BLV infected cattle, the event and identification of the cattle involved were recorded. Serologic testing was performed ei ght times during the 22 month study to determine the number of animals that became infected following a palpation (an event), Thirty-one ani mals seroconverted during the study; 24 in the treatment (no sleeve ch ange) group and seven in the sleeve change group. Sixteen of the anima ls in the treatment group that seroconverted had been palpated prior t o their seroconversion. A hazard ratio (relative risk) for BLV serocon version was determined between the two groups. Cows palpated with no s leeve change had a 2.8-fold increase in risk (confidence interval 1.1- 6.8) of BLV infection. The increased risk of BLV infection associated with rectal palpation may have been affected by the presence of some h ighly infectious cows in the herd. This study confirms that rectal pal pation without a change of sleeve may be a significant risk factor in some herds, and if efforts are made to decrease the spread of BLV in a herd, the potential for rectal sleeve transmission must be considered .