Influence of pre- and post-pubertal grazing regimes on adult testicular morphology in extensively reared Corriedale rams

The aim of the present study was to determine whether pre- and post-puberta l young rams on different grazing regimes, resulting in differences in live weight (LW), would show corresponding differences in testicular growth or testicular morphometry that could influence the reproductive traits of thes e rams upon reaching adulthood, Forty-one spring-born Corriedale rams were reared on either native pasture (low feeding level, Group L, n = 22) or imp roved pasture (higher feeding level, Group H, n = 19) from 1 to 7 months of age, Thereafter, half the animals in the native-pasture group were placed on improved pasture and vice versa, thus creating an additional four differ ential-grazing treatment groups (Groups LL, n = 11; LH, n = 11; HL, n = 10; and HH, n = 9). Animals were managed in this way until 18 months of age. H alf the animals from each group were then castrated and their testes were s ubjected to morphometric analysis. The remaining animals (Groups LL. n = 6; LH, n = 6; HL, n = 5; and HH, n = 4) were managed together until 30 months of age (from 18 to 27 months on native pastures and from 27 to 30 months o f age on improved pastures, at a stocking rare of two to three rams pet hec tare), whereupon they were also castrated for testicular morphometry. LW an d scrotal circumference (SC) were recorded every 60 days. The stereological analysis of testicular parenchyma included counts of elongated spermatids and Sertoli cells. Differences (P < 0.001) in LW were observed between feed ing levels, even at 30 months of age. Differences (P < 0.001) in SC existin g at the end of the differential treatment (18 months of age) disappeared ( n.s.) soon after. Most differences (P < 0.05) in testicular morphometry exi sting at the end of the differential treatments were no longer significant 1 year later. It is concluded that changes in grazing management during pre - and post-pubertal periods can induce short-lived differences in testicula r post-natal growth in Corriedale rams bur do nor influence testicular morp hology or function later in lift. (C) 2000 Elsevier Science B.V. All rights reserved.