Influence of grazing management on the seasonal change in testicular morphology in Corriedale rams

The present study was conducted: (a) to determine the degree of seasonal va riation in testis stereology in Corriedale rams between autumn and winter; (b) to test the hypothesis that testis stereology of Corriedale rams grazin g native pastures during autumn and winter would differ from those of Corri edale rams grazing sown pastures and supplemented with grain during the sam e period; and (c) to determine whether Sertoli cell numbers differ in adult rams between the breeding season (autumn) and the following non-breeding s eason (winter). Twenty experimental animals were studied. Six rams (autumn control group, C-A) that had been grazing on native pasture (stocking rate = 2-3 animals ha(-1)) were castrated at the beginning of the experiment (Ma rch, early autumn). Seven rams (winter control group, C-W) continued to gra ze on native pasture at the same stocking rate until the end of the experim ent (August, late winter). Another seven rams (treated group, T) grazed on improved pasture (stocking rate = 1-2 animals ha(-1)) and were supplemented with 1 kg grain ram(-1) day(-1) until the end of the experiment. Live weig ht, scrotal circumference, serum testosterone concentration and selected te sticular stereological parameters were measured. The treatment did not impe de the winter reduction in testicular activity and reduced its magnitude sl ightly (group T) compared with controls (group C-W). Sertoli cell numbers w ere higher in autumn (group C-A) than in winter, both on native (group C-W) and sown pastures (group T). Diminishing Sertoli cell numbers between autu mn and the following winter suggest the occurrence of that Sertoli cell dea th during this period. The results indicate that, although the reproductive activity of Corriedale rams is moderately seasonal, a restricted change in grazing and grain supplementation can only modify it to a limited extent. (C) 1999 Elsevier Science B.V. All rights reserved.