Martin G B, Walkden-Brown S W
School of Agriculture, University of Western Australia, Nedlands.
J Reprod Fertil Suppl. 1995;49:437-49.
Changes in the nutrition of mature rams and goat bucks lead to profound responses in testicular size and therefore the rate of production of spermatozoa. These effects are largely due to changes in the size of the seminiferous tubules and in the efficiency of spermatogenesis. With the exception of severe undernutrition, the effects on spermatogenic function are not accompanied by similar changes in endocrine function of the testes, as measured by the production of testosterone or inhibin. In rams, moderate changes in nutrition affect gonadotrophin secretion for only a few weeks, whereas testicular growth is affected for several months. In mature male goats during the non-breeding season, nutrition-induced testicular growth does not seem to be associated with a gonadotrophin response. Such observations have led us to develop the hypothesis that nutrition-driven testicular growth is at least partly independent of changes in gonadotrophin secretion. The energetic components of the diet, rather than the protein content, seem to be responsible for affecting gonadotrophin secretion in rams. The volatile fatty acids, and not glucose, are the active factors, although intracerebral insulin may also play a role. Where these substrates act and whether they are also involved in the gonadotrophin-independent pathways requires testing. In conclusion, nutritional signals exert powerful effects on the reproductive system of mature male ruminants, and the responses are partly independent of changes in gonadotrophin secretion. In the gonads, the gametogenic tissue responds rapidly to changes in nutrition, but the endocrine compartments are less affected. Variations in the expression of the nutritional responses among sexes, breeds and species probably reflect variations in the role of this environmental factor as a modulator of reproductive function.
成年公羊和种用公山羊营养状况的改变会导致睾丸大小产生显著变化，进而影响精子生成速率。这些影响主要归因于生精小管大小的改变以及精子发生效率的变化。除了严重营养不良外，对精子发生功能的影响并未伴随睾丸内分泌功能出现类似变化，这可通过睾酮或抑制素的分泌来衡量。在公羊中，营养状况的适度改变仅在几周内影响促性腺激素分泌，而睾丸生长则会受到数月的影响。在非繁殖季节的成年雄性山羊中，营养诱导的睾丸生长似乎与促性腺激素反应无关。这些观察结果促使我们提出这样的假设：营养驱动的睾丸生长至少部分独立于促性腺激素分泌的变化。日粮中的能量成分而非蛋白质含量似乎是影响公羊促性腺激素分泌的原因。挥发性脂肪酸而非葡萄糖是活性因子，尽管脑内胰岛素可能也发挥作用。这些底物的作用部位以及它们是否也参与不依赖促性腺激素的途径尚需验证。总之，营养信号对成年雄性反刍动物的生殖系统具有强大影响，且这些反应部分独立于促性腺激素分泌的变化。在性腺中，配子发生组织对营养变化反应迅速，但内分泌部分受影响较小。性别、品种和物种之间营养反应表达的差异可能反映了这一环境因素作为生殖功能调节因子的作用差异。
