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Abstract
The purpose of this study was to examine the hypothesis that rams of a tropical breed may be more effective than rams of temperate breed in inducing a reproductive response in ewes of temperate origin during the anoestrous period. Thirty Suffolk ewes in seasonal anestrus were assigned to one of three groups. In the control group (n=9), no males were present, while in the second group (Suffolk rams [SUF]; n=9) ewes were exposed to Suffolk males continuously for 13 days and twice per day from days 14-30, while in the third (Saint croix rams [SCR]; n=12), ewes were treated as in SUF, but rams were from the Saint Croix breed. Sexual receptivity was recorded daily for 30 days after introduction of the males and lambing data were recorded in the fall in SUF and SCR groups. In addition, serum progesterone (P4) concentration was used to monitor ovarian activity in all groups. No reproductive activity was observed in controls. In SUF, six ewes ovulated but did not show estrus, while in SCR all ewes showed estrus, ovulated and were mated. In addition, all but one of the ewes in SCR lambed. It was concluded the Saint Croix rams were more effective than Suffolk rams in inducing an estrous response, conception and pregnancy in anestrous Suffolk ewes.