Ability of castrate male sheep treated with oestrogen or testosterone to induce and detect oestrus in ewes
1981
Fulkerson, W.J. (University of Western Australia, Nedlands (Australia). Dept. of Animal Science and Production) | Adams, N.R. | Gherardi, P.B.
Four experiments were conducted to determine if castrate male sheep (wethers), treated with testosterone or relatively high doses of oestrogens, could replace vasectomised rams in inducing anoestrous ewes to commence breeding out of season, and in detecting and mounting ewes in oestrus for subsequent artificial insemination or after mating for isolating "empty" ewes. Widespread usage of vasectomised rams on farms is hampered by the cost of the vasectomy operation and problems associated with handling the animals. Wethers were treated three times at weekly intervals with 1 mg Oestradiol Cypionate in oil or 105 mg testosterone propionate in polyethylene glycol. Male behaviour of wethers treated with oestrogen and testosterone was similar and comparable to vasectomised rams. Masculine behaviour developed at about the time of the third injection and lasted for at least five weeks. Untreated wethers showed no male behaviour. Wethers treated with either hormone were able to stimulate anoestrous ewes to ovulate after contact for six days. This response was at least as good as with vasectomised rams, whereas untreated wethers had no effect on the ewes. A comparative study under field conditions, using 5251 ewes, showed that testosterone-treated wethers were as good as vasectomised rams at inducing anoestrous ewes to ovulate and at detection of ewes in oestrus. The practical implications of this work are discussed.
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