Effect of dietary energy on seminal plasma insulin-like growth factor-I (IGF-I), serum IGF-I and testosterone levels, semen quality and fertility in adult rams

Abstract

The objective of the present study was to modulate seminal plasma insulin-like growth factor-I (IGF-I) by dietary energy and assess the relationship among testosterone and IGF-I levels, semen quality and fertility in adult rams. Twenty-four 1-yr old adult Nellore rams were equally divided into three groups (n = 8) and fed with three different concentrate mixtures formulated using conventional ingredients and finger millet (Eleucine corocana) straw to ensure rams received with similar amount of crude protein with three levels of energy. Rams in low-energy group were offered diets with 20% less energy than the control energy group (optimum energy, 100%, recommended energy level), whereas rams in high energy group were offered diets with 20% more energy than the optimum energy group. Semen was collected from rams 60 days after start of the experimental feeding. The percentages of progressive forward motility, functional membrane integrity and mitochondrial membrane potential of the spermatozoa were significantly (P < 0.05) higher in control and high energy groups as compared to low-energy group. Feeding of low-energy diet significantly (P < 0.05) decreased spermatozoa VSL, VCL and VAP when compared to control and high energy fed groups. The number of spermatozoa binding/oocyte was significantly (P < 0.05) higher in control (11.23 ± 0.20) and high energy (10.57 ± 0.19) groups as compared to the low energy (6.14 ± 0.01) group. The serum and seminal plasma IGF-I levels were significantly (P < 0.05) higher in control and high energy fed groups as compared to the low-energy group. The serum testosterone and cholesterol levels were significantly (P < 0.05) higher in the control group as compared to the low-energy group. The seminal plasma fructose levels in optimum energy fed animals were significantly (P < 0.05) higher as compared to other two groups. The seminal plasma IGF-I level had positive correlation with progressive forward motility (r = 0.7) and other velocity (linearity, r = 0.7; straightness, r = 0.7) parameters. The study suggested that the modulation of seminal plasma IGF-I levels by dietary energy is possible and the optimum level of seminal plasma IGF-I is necessary and sufficient to influence semen quality.