Growth and reproductive responses of goat bucks to range grazing and concentrate-based production systems

This study aimed to evaluate the effects of range grazing and three concentrate-based production systems on the growth, sexual behavior, scrotal circumference, and semen quality of breeding bucks. A total of 40 yearling bucks (10 bucks/treatment) were randomly allocated to range grazing (T1) and three different roughage-to-concentrate ratios: 60:40% (T2), 50:50% (T3), and 40:60% (T4) on a DM basis for a period of 90 days. All data were analyzed via ANOVA in SAS-JMP Pro 19. Bucks in T3 and T4 presented greater average daily gains (ADG) than those in T1 and T2 did, although T2 presented better gains than did T1. In T1 bucks, scrotal development, the number of mounts, the frequency of ejaculation, the courtship behavior score, and the testosterone concentration were lower, whereas the reaction time and refractory period were greater than those in T3 and T4. Bucks fed the T4 diet presented greater semen volume, followed by those fed T3 and T2, and the lowest semen volume was observed at T1. Strong positive correlations were observed between dry matter intake (DMI), scrotal circumference, and semen volume. ADG was also strongly correlated with semen volume (r = 0.81), motility (r = 0.78), and scrotal circumference (r = 0.82). The results of this study indicated that concentrate-fed bucks had better daily gain, scrotal development, and functional semen quality traits (semen volume, motility, and concentration) than did range grazing bucks, although the ADG, feed conversion efficiency, and mating frequency of the bucks fed the T3 and T4 diets were similar.