Dietary Protein Imbalance Impairs Sperm Morphology and Promotes Testicular Degeneration in Rams

Reproductive efficiency is a primary determinant of profitability in ruminant production, with male fertility being a critical factor for genetic progress and herd productivity. While nutritional management is a central component in modulating reproductive capacity, the effects of excessive dietary protein on testicular function remain incompletely elucidated. This study evaluated the impact of different dietary crude protein (CP) levels on reproductive and metabolic parameters in rams. Twenty-eight Santa Inês rams were randomly assigned to four groups (n = 7) and fed for 120 days with isoenergetic diets containing distinct CP levels: control (13.4%), hypoproteic (11.4%), hyperproteic I (17.5%) and hyperproteic II (22.4%). Periodic evaluations of body parameters, sperm kinetics and morphology, testicular ultrasonography, testicular cytology and hormonal profiles were conducted. Diets did not influence body weight or sperm motility (p > 0.05). However, variations in testicular echogenicity were observed (p < 0.05), and rams fed hyperproteic diets showed a progressive and marked increase in total sperm defects, exceeding 29.5% on day 80 (p < 0.05) compared with the control group (12.86%). Cytological analysis confirmed the presence of multinucleated giant cells and testicular degenerative changes from day 40 onwards in the hyperproteic groups. In conclusion, diets containing 17.5% and 22.4% CP are detrimental to sperm morphology and testicular integrity in rams, even in the absence of changes in body weight or detectable ultrasonographic alterations. The diet with 13.4% CP proved more suitable for maintaining testicular function and reproductive health.