Effect of undegradable protein supply on testicular size, spermiogram parameters and sexual behavior of mature Assaf rams.

Eighteen mature Assaf rams were used to study the effect of undegradable protein (UDP) supply on testicular size, sperm production and quality, testosterone secretion and reproductive behavior. Animals were allocated to three groups of six animals each and fed during 10 weeks with different diets which were designed to supply approximately 0.5MJ of metabolisable energy (ME)/kg LBW(0.75) and 9g of effective rumen degradable protein (ERDP)/MJ of fermentable ME to all animals and to induce differences in rumen UDP intake (0.97, 1.72 and 3.08g of UDP/kg LBW(0.75) for LP, MP and HP diets, respectively). Neither plasma testosterone concentration nor reproductive behavior parameters (number of services, number of mounts without ejaculation and reaction time to first mount) were affected (P > 0.05) by protein intake. Nevertheless, there were significant (P < 0.05) differences between diets in both testicular size and sperm production. Scrotal circumference was lower in LP compared to MP and HP groups, no significant differences being observed between these latter two groups at any time. In relation to sperm production, the lowest and the highest values were always observed in LP and HP groups, respectively. MP group showed intermediate values, significantly different from those of LP and HP groups on Week 5 and only from those of LP group on Week 9. The present results provide a better understanding of the effect of protein nutrition and suggest that UDP should be supplied to Assaf rams during the mating season to improve their reproductive performance.