Ability of androgenized goat wethers and does to induce estrus in goats under extensive conditions during anestrus and breeding seasons

Abstract

Two hundred and ten Criollo crossbred goats under extensive conditions were randomly allotted to treatments to measure effects of exposure to intact bucks (♂), androgenized wethers (W) or androgenized does (♀), during the breeding season (November), on estrus response. Castrated bucks were androgenized by injecting 60 mg of testosterone propionate every 3 days for 20 days and every 4 days during the teasing period. Does were given 300 mg of testosterone during 2 consecutive days, additional 300 mg on Day 5 and 60 mg every 4 days. After 13 days of stimulus, induction of estrus did not vary among teasers (87.1, 94.3 and 84.0% for ♂, W and ♀, respectively) but time to onset of estrus was significantly shorter ( P < 0.01) for goats exposed to ♂ (4.6 ± 0.40 days) compared with goats exposed to W (6.9 ± 0.39 days) and ♀ (8.1 ± 0.46 days). In another experiment conducted during the non-breeding season (April) a total of 150 goats were divided into two groups and exposed either to ♂ or W. After 37 days of teasing the proportion of does exhibiting behavioral estrus was half of that observed during the breeding season. There was no significant effect of teasers on estrus response (46.7 and 51.7% for ♂ and W, respectively) but the time to onset of estrus was shorter for ♂ (27.3 ± 0.66) compared with W (30.7 ± 1.26). Results of a third experiment showed that pregnancy rate (76.5% vs 24.7%) and prolificacy (1.61 ± 0.04 vs 1.25 ± 0.08) was affected ( P < 0.01) by month of breeding (January vs April). Results demonstrate that androgenized wethers and testosterone-treated does can be used successfully to induce estrus during the breeding season of goats, but that, under these conditions, only half of the does respond to this teasing during the non-breeding season, which leads to poor reproductive performance when goats were exposed to bucks during the non-responsive anovulatory period.