Effect of nutritional state on semen characteristics, testicular size and serum testosterone concentration in Sanjabi ram lambs during the natural breeding season

Abstract

This experiment was conducted to investigate the effect of plane of nutrition on body weight, average daily gain, dry mater intake, semen characteristics, serum testosterone concentration and testicular circumference of Sanjabi ram lambs during the natural breeding season. Sanjabi ram lambs (n = 20) that were 8 months of age were penned under natural photoperiod at latitude 34°18'N for a period of 9 months. The control group (C, n = 10) received a diet consisting of 80% alfalfa and 20% concentrate, providing 2.18 Mcal metabolizable energy and 130.0 g /kg DM crude protein, whereas, treatment group (T, n = 10) was fed with 65% alfalfa and 35% concentrate, providing 2.34 Mcal metabolizable energy and 160.0 g/kg DM crude protein. Body weight, additive daily gain and feed intake in T group were significantly greater than those obtained in C group. Body weight and testicular circumference increased at a steady rate throughout the experiment. All semen variables (except percentage of abnormal sperm and semen pH), serum testosterone concentration and testicular circumference were positively influenced by nutritional state (P < 0.05). Interaction of nutritional state with season was found for semen volume, sperm concentration and abnormal sperm, but there was no interaction on the total sperm, progressive motility, live sperm, semen pH and semen index. It is concluded that the reproductive activity of growing Sanjabi ram lambs is affected by nutritional state. These results also demonstrated a monthly pattern in reproductive characteristics of Sanjabi ram lambs, independent of the nutritional state.

Keywords: Photoperiod; Semen index; Sheep; Sperm; Sperm motility; Testicular circumference.