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.