The effect of nutrition on testicular growth in the Merino ram

Abstract

Fifteen rams were used in a series of three experiments in which different nutritional treatments were allocated to groups of 5 individually housed animals (3 treatments per experiment). In all experiments one group received only the basal ration (1 kg/day of a pelleted diet) and a second group was fed this ration plus 750 g/day of lupins. The remaining three treatments were: (1) the basal ration plus an intra-abomasal infusion of casein (200 g/day) and glucose (1 12 g/day); (2) a pelleted diet consisting of the basal ration plus oil (60 g/day) and VFA salts (255 g/day), together with an intra-abomasal infusion of casein (200 g/day) and glucose (112 g/day), and (3) the basal ration plus 800 g/day of barley. Experiments were carried out over a period of 42-49 days and measurements were made of testicular size, wool growth, liveweight and digestibility of the diets. The results of this study were compared with those of a number of published and unpublished experiments. Testicular growth was highly correlated (r= 0.86) with liveweight change in a curvilinear relationship. Change in liveweight and respiration rate were highly correlated with digestible energy intake (r=0.79 and r=0.94 respectively). Wool growth was highly correlated (r=0.97) with crude protein intake and nitrogen balance, with digestible energy having only a marginal influence. There was also a high correlation (r= 0.85) between digestible energy intake and testicular growth, with dietary protein having only a marginal influence. Comparison of these data with published data on testicular growth in rams confirmed the above relationships. It was concluded that testicular growth in rams responds more to digestible energy intake and liveweight change than to crude protein availability.