Effect of ram introduction and hormonal treatment on fertility in seasonally anestrous Suffolk ewes raised under different photoperiod during perinatal period
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概要
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This study was conducted to examine fertility in out-of-seasonal breeding using practical treatments available to sheep farm.<BR>Thirty-three Suffolk ewes were supplemented artificial light (L, n =18) or maintained on natural daylength (N, n =15) during perinatal period (February to March). All ewes gave birth to lambs. After weaning, Seasonally anestrous those ewes were divided into following 3 groups : <BR>Group A (L : n = 5, N : n = 6), ewes were introduced fertile ram for 38 days from May 26 ;<BR>Group B (L : n =7, N : n =4), ewes were introduced ram similarly to group A, and given an injection of PMSG at May 26 followed 13 days later (June 8) by an injection of PMSG and PGF <SUB>2α</SUB> ;<BR>Group C (L : n = 6, N : n = 5), ewes were introduced fertile ram for 25 days from June 8, and given hormonal injections similarly to group B. <BR>Returns to service were monitored for three consecutive cycles and this was facilitated by changing the raddle colour every 13 days. <BR>The incidence of estrus in groups A, B and C was 45%, 82% and 36%, respectively. The incidence of estrus in group B was higher than that of group C (P < 0.05). The conception rate was identical between group A and B (45%), but that in group C was 9%. The incidence of estrus in ewes supplemented artificial light during perinatal period was higher than that in ewes maintained on natural daylength (78%, 14/18 vs. 27%, 4/15, P < 0.01). The conception rate in ewes supplemented artificial light was higher than that in ewes maintained on natural daylength (50%, 9/18 vs. 13%, 2/15, P < 0.05). <BR>The present results suggested that Suffolk ewes raised in Hokkaido, supplemented artificial light during perinatal period (February to March), were responsive to 'male effect' in late May, and the additional hormonal treatment using PMSG and PGF<SUB>2</SUB>α induced cyclic estrous activity in these ewes, which could be one of the out-of-seasonal breeding systems in practice.
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