The control of oestrus, ovulation and fertility in relation to artificial insemination in the Angora goat

Abstract

A total of 792 purebred and crossbred Angora does was used in an artificial insemination (AI) program. Does were treated with intravaginal pessaries containing 20 mg 'Cronolone' or with a single intramuscular injection of 100 µg of the prostaglandin analogue 'Estrumate' (I.C.I.) to control the time of oestrus, or they remained untreated. Pessaries were left in situ for 16, 18 or 20 days, while Estrumate was given 6–11, 13–16, or 18–20 days after oestrus or at unknown times after oestrus. After treatment the does were run with harnessed vasectomized bucks, and they were inspected for oestrus at 12-h intervals. Does in oestrus were inseminated 0–2 or 12–14 h after the detection of oestrus, and each doe received 0.1 ml semen collected by electroejaculation from Angora bucks. Treatments and results were: (1) pessaries—232 does treated and retained pessaries, 167 (72%) inseminated of which 82 (49%) kidded; (2) Estrumate at known times—115 does treated, 83 (72%) inseminated of which 36 (43%) kidded; (3) Estrumate at unknown times—151 does treated, 72 (48%) inseminated of which 40 (56%) kidded; (4) untreated—277 does, 223 (81%) inseminated of which 149 (67%) kidded. Time of AI after the detection of oestrus had little effect on kidding performance. In does treated with Estrumate at known times the majority (82%) were in oestrus 48–72 h after treatment with no effect of time of treatment on incidence of oestrus, or on fertility. Oestrus after removal of pessaries occurred 12–24 h earlier than after Estrumate, and there were effects of duration of insertion of pessaries on the time, and precision in time of oestrus. Oestrus occurred earlier and with less precision as the duration increased, and there was a suggestion of lowered fertility in does treated for 20 days, which indicated that the dose of Cronolone used in the pessaries was marginal. Overall, treatment depressed fertility, but the kidding performance of does treated with pessaries for 16 days and in oestrus 36-60 h after removal of pessaries approached that of untreated does (61 v. 67%).