Under-nutrition reduces spermatogenic efficiency and sperm velocity, and increases sperm DNA damage in sexually mature male sheep

We tested whether the quality of spermatozoa from mature male sheep would be affected during nutrition-induced changes in testicular mass. Merino rams were fed for 65 days with diets that increased, maintained or decreased body and testis mass (n = 8 per group). In semen collected on Days 56 and 63, underfed rams had less sperms per ejaculate than well-fed rams (P < 0.05) and a lower sperm velocity (computer-assisted semen analysis) than well-fed or maintenance-fed rams (P < 0.05). Sperm chromatin structure assay revealed more sperm DNA damage in underfed rams than in well-fed rams (P < 0.05). The amount of sperm DNA damage was inversely correlated with change in scrotal circumference (r = −0.6, P < 0.05), the percentages of progressive motile sperm (r = –0.8; P < 0.01) and motile sperm (r = −0.6, P < 0.05), and the numbers of sperms per gram of testis (r = −0.55, P < 0.05). In testicular tissue collected on Day 65, underfed rams had fewer sperm per gram of testis than rams in the other two groups (P < 0.001). We conclude that, in adult rams, underfeeding reduces spermatogenic efficiency and that this response is associated with a reduction in spermatozoal quality.