Reproductive activity of Suffolk ewes in seasonal anestrus after being exposed to Saint Croix or Suffolk rams

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 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.

Annual variation in reproductive parameters and sexual behaviour of Saint Croix rams in a semi-desert region in Mexico

“…Despite these decreases in T in the first months of the year, this is not an impediment for the rams to have a sufficient sexual activity to stimulate the presence of oestrus in Saint Croix ewes (Aguirre et al 2007) or in wool breed ewes (Clemente et al 2012). Considering that, at these latitudes, there is a seasonal anestrus during the first half of the year and more marked in wool sheep breeds (Aller et al 2012).…”

“…However, despite this low sexual behaviour, it is interesting to notice the ability of the Saint Croix rams to establish strategies and dosage of their mating. Clemente et al (2012) report that Saint Croix rams were able of inducing oestrus in and out of the breeding season in Suffolk sheep. Aguirre et al (2007) evaluated the effect of social hierarchy and reported that even the subordinate rams can keep acceptable sexual behaviour and were able to present a greater proportion of lambing throughout the year, as reported by Godfrey et al (1998) and Sanchez-Davila et al (2015).…”

La conducta sexual del carnero. Revisión

“…Además, en las regiones tropicales o de transición hacia climas templados, existe la posibilidad de usar carneros de razas de pelo, quienes sufren poco o nulo efecto estacional (130,147,148) , para estimular borregas de razas con temporadas reproductivas más marcadas. Clemente et al (149) encontraron que carneros Santa Cruz indujeron estro, concepción y preñez en borregas Suffolk anéstricas en comparación subtropical environments some breeds may be very little or not affected by seasonal variations in day light hours (178) or temperature (76,179) , but by changes in the provision of feed during the year (180) .…”

“…In addition, in tropical regions, or transitional temperate climates, there is the possibility of using hair breeds rams, who suffer little or no season effect (130,147,148) , to stimulate ewe breeds with more pronounced reproductive seasons. Clemente et al (149) found that Santa Cruz rams induced oestrus, conception and pregnancy in Suffolk anestric ewes while Suffolk rams only caused silent ovulations in ewes of their same breed (at 19° N). This is explained at least in part, due to the difference in the magnitude of courtship behavior emitted by both breeds during the long days season (52) .…”

Induction of fertile estrus without the use of steroid hormones in seasonally anestrous Suffolk ewes

“…However, Nugent and Notter [15] improved the effectivity of the ram effect in Suffolk ewes by mixing them with less seasonal white-faced ewes, which probably amplified the effect of the males by female-to-female stimulation [17]. Also, Clemente et al [18] found an improved response of Suffolk ewes to the male effect when rams of a low-seasonality breed were used for stimulation. The results of those studies suggest that the male effect can be effective in Suffolk ewes if the stimulus is intense enough.…”