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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 09), no males were present, while in the second group (Suffolk rams [SUF]; n 09) 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]; n012), 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 (P 4 ) 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.

Equine chorionic gonadotrophin (eCG or PMSG) is a hormone with FSH/LH effect that has been widely used in ewes and cows to induce follicle development. However, the possible positive effects of its administration to males have been rarely studied. ECG stimulates testosterone secretion and increases rams’ ability to stimulate ovulation in anoestrous ewes (the ‘ram effect’), but it is still not known if this effect is at least partially explained by an enhancement of a ram’s sexual behaviour. Thus, the aim was to determine if the administration of eCG induces an increase in testosterone concentration, and thus improves sexual behaviour of Saint Croix rams during both the breeding and the non-breeding seasons. Two doses of 1000 IU of eCG were administered separated by 4 days to 10 rams during the breeding and five rams during the non-breeding seasons, with the same number of animals as untreated controls. Administration of eCG increased testosterone concentration during the breeding (P = 0.008) and the non-breeding (P = 0.0009) seasons. The number of ano-genital sniffings, lateral approaches, as well as total courtship behaviours were greater in treated than untreated rams during the breeding season. Treated rams also tended to mount and mate more during the breeding season. During the non-breeding season, treated rams tended to display more ano-genital sniffs, lateral approaches and total courtship behaviours than untreated rams 6 days after the first dose. Overall, eCG increased testosterone concentrations the breeding and the non-breeding seasons, and was associated with a greater display of sexual behaviours during the former.

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