The effect of dietary energy levels on the sexual puberty of ram lambs

Aim of study: To evaluate the effect of different feeding levels on body weight changes, sexual behavior activities, and spermatogenesis characteristics of testis tissue in immature Iranian breed lambs. Area of study: University of Tabriz, Iran. Material and methods: A total of 40 (start of experiment, 4; after 6 months, 12; 9 months, 12; sexual behavior, 12) two-month-old immature ram lambs were divided into three equal groups and were fed for eight months with three different concentrate mixtures formulated using conventional ingredients based on barley grain. Lambs received the same amount of crude protein with three levels of energy. The diet of the low-energy (LE) group had an energy of 10% lower than the control group, which received a diet with optimum energy of 100% according to the NRC. Lambs in the high-energy (HE) group were fed diets with an energy of 10% higher than the optimum energy group. In each group, four lambs were castrated in three steps, including the ages of 2 (start of treatment), 6, and 9 months. Body weight and scrotal circumference were recorded monthly. Sexual behaviors toward estrus ewes were evaluated for 30 min, and the testes were analyzed histologically. Main results: The lambs in the LE group had lower body weight and smaller scrotal circumference than HE group (p<0.05). Sexual behaviors in the HE group occurred at an earlier age, such as mount and mounts with ejaculation, as the external presentations of puberty (p<0.05).    Research highlights: Underfeeding of pre-pubertal animals delayed puberty, while high-plane feeding advanced puberty.