EFFECTS OF IVERMECTIN ON REPRODUCTIVE FUNCTIONS IN EWES

In response to producers' concerns about possible detrimental effects of ivermectin on ewes during the breeding season, an evaluation of its effects on endocrinological, physiological, and behavioral measures o f reproductive performance was made. Twenty cycling ewes were randomly assigned on d 10 (d 0 = estrus) to receive a single recommended oral dose of 200 mug/kg of BW of ivermectin or a control volume of water. T welve hours after treatment, ewes received a luteolytic injection of 5 mg of PGF2alpha and were introduced to fertile rams. On d 10 after ma ting, laparoscopies were performed to assess ovulation rate, and on d 18 conceptuses were surgically recovered. Blood samples were collected during the 92-h interval beginning immediately before ivermectin and control treatments and were assayed for LH. It was determined that 1) interval from PGF2alpha-induced luteal regression to a) onset of estru s (36.1 +/- 1.4 vs 36.3 +/- 1.4 h) and b) onset of the preovulatory su rge of LH (38.2 +/- 2.6 vs 44.2 +/- 2.6 h), 2) magnitude of the surge of LH (275.6 +/- 38.9 vs 199.8 +/- 38.9 ng/mL), 3) duration of the sur ge of LH (9.4 +/- .4 vs 9.0 +/-.4 h), 4) area under the curve of the s urge of LH (54,321 +/- 7,419 vs 38,138 +/- 7,419 arbitrary units), 5) ovulation rate (2.1 +/- .4 vs 2.0 +/- .3 ovulations/ewe), 6) pregnancy rate (8/10 vs 5/10 ewes pregnant), and 7) conceptuses per ewe (1.75 /- .37 vs 1.60 +/- .33) did not differ (all P > .1) between ivermectin - and control-treated ewes, respectively. We conclude that these data do not support concerns that ivermectin has a detrimental effect on th e reproductive performance of ewes during the breeding season.