Centre Interrégional d'Information et de Recherche en Production Ovine, Site Expérimental du Mourier, 87800 St Priest Ligoure, France.
Anim Reprod Sci. 2010 Jun;119(3-4):205-11. doi: 10.1016/j.anireprosci.2010.02.003. Epub 2010 Feb 11.
In seasonally anoestrous ewes of many breeds, the introduction of rams triggers an increase in gonadotrophin secretion that induces ovulation, a phenomenon known as the 'ram effect'. The ram effect is a practical method for mating ewes outside the natural breeding season, and also can provide synchronised lambing, but the variability of the response, especially in young animals, reduces its potential for widespread application. The aim of our study was to assess two factors that are thought to contribute to the variability in young ewes: temperament and sexual experience. We used anovulatory ewes from a flock that had been genetically selected for 'calm' or 'nervous' temperament and compared the endocrine and ovarian responses to the ram effect in four groups (each n=15): 'calm' and parous (3-6 years old); 'calm' and nulliparous (2 years old); 'nervous' and parous; and 'nervous' and nulliparous. Parous ewes, independently of their temperament, exhibited a faster endocrine response and a higher proportion of females cycling after ram introduction than nulliparous ewes. 'Nervous' ewes exhibited a higher proportion of females cycling after ram introduction than calm ewes, but only in the nulliparous group. We conclude that temperament exerts little influence on the response to the ram effect in sexually experienced ewes, and that females of 'nervous' temperament appear to respond better when sexually 'naive'. Both sexual experience and temperament need to be taken into consideration when flock management involves the ram effect. Finally, some ewes were cyclic at ram introduction, yet exhibited an increase in LH secretion even in the presence of high concentrations of progesterone. The mechanism by which the inhibitory effect of progesterone on LH secretion was bypassed needs to be clarified.
在许多品种的季节性乏情母羊中，公羊的引入会触发促性腺激素分泌的增加，从而诱导排卵，这一现象被称为“公羊效应”。公羊效应是在自然繁殖季节之外配种母羊的一种实用方法，也可以提供同步分娩，但由于反应的可变性，尤其是在年轻动物中，降低了其广泛应用的潜力。我们的研究目的是评估两种被认为会导致年轻母羊反应变异性的因素：气质和性经验。我们使用来自一个经过遗传选择的羊群的乏情母羊，这些母羊的气质被选择为“冷静”或“紧张”，并比较了四个组（每组 n=15）的内分泌和卵巢对公羊效应的反应：“冷静”和经产（3-6 岁）；“冷静”和初产（2 岁）；“紧张”和经产；以及“紧张”和初产。无论气质如何，经产母羊的内分泌反应更快，引入公羊后有更多的母羊发情。与冷静的母羊相比，紧张的母羊在引入公羊后有更多的母羊发情，但仅在初产组中如此。我们得出结论，气质对有性经验的母羊对公羊效应的反应影响不大，而具有“紧张”气质的母羊在性“幼稚”时似乎反应更好。在涉及公羊效应的羊群管理中，需要考虑性经验和气质。最后，有些母羊在引入公羊时已经发情，但即使在高浓度孕激素存在的情况下，LH 分泌也会增加。需要阐明孕激素对 LH 分泌的抑制作用是如何被绕过的。
