EFFECT OF EWE OVINE LENTIVIRUS INFECTION ON EWE AND LAMB PRODUCTIVITY

We used a previously described sensitive and specific ovine lentivirus (OLV) recombinant transmembrane (rTM) protein enzyme-linked immunosor bent assay (ELISA) to detect anti-OLV antibodies and define OLV infect ion in breeding ewes from nine US Meat Animal Research Center (MARC) f locks. We estimated the production impacts of dam rTM ELISA seropositi vity on ewe and lamb productivity in the birth-to-weaning interval usi ng production data from 1466 breeding ewes (of which 1242 actually lam bed) and their 2452 lambs born in spring 1992 using several multiple l inear and logistic regression models. By adjusting for lamb weaning ag e, gender, type of birth and rearing, birth difficulty, dam age, and f lock, the component of ewe or lamb productivity related to ewe OLV inf ection alone was isolated. The rTM ELISA-negative ewes produced signif icantly more total weight of weaned lamb per ewe-lambing (3.84 kg) and per ewe ram-exposed (4.95 kg) compared to their OLV-positive flockmat es. Negative ewes also weaned 0.11 more lambs per ewe-lambing and 0.09 more lambs per ewe ram-exposed, gave birth to 0.13 more lambs per ewe ram-exposed, and were more likely to lamb after breeding (odds ratio (OR) = 1.9) compared to equivalent OLV-positive ewes. Lambs reared by OLV-negative ewes weighed 0.15 kg more at birth, gained 8 g more per d ay through weaning, and weighed 0.59 kg more at 56-day weaning. Prewea ning mortality was lower (OR = 0.8) among lambs born to OLV-negative c ompared to OLV-positive ewes, although this difference was not signifi cant. Our results suggest that subclinical OLV infection has important detrimental effects on sheep production which occur in cumulative fas hion from breeding through weaning and that OLV control efforts may be financially justified in some sheep flocks. (C) 1997 Elsevier Science B.V.