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 of 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 micrograms/kg of BW of ivermectin or a control volume of water. Twelve hours after treatment, ewes received a luteolytic injection of 5 mg of PGF2 alpha and were introduced to fertile rams. On d 10 after mating, 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 PGF2 alpha-induced luteal regression to a) onset of estrus (36.1 +/- 1.4 vs 36.3 +/- 1.4 h) and b) onset of the preovulatory surge 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 surge of LH (9.4 +/- .4 vs 9.0 +/- .4 h), 4) area under the curve of the surge 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.(ABSTRACT TRUNCATED AT 250 WORDS)