Supplementation with Proline Improves Haemato-Biochemical and Reproductive Indicators in Male Rabbits Affected by Environmental Heat-Stress

Twenty-four adult rabbit bucks (<i>n</i> = 6 per treatment) were fed a basal diet supplemented with 0 (control), 50, 100, and 150 mg proline/kg dry matter (DM) diet for 12 weeks to determine possible usefulness for alleviating the negative impact of environmental heat stress on redox status, haemato-biochaemical attributes and semen quality. There were significant dose–response effects, with increments in levels of dietary proline (LDP) quadratically improving red blood cell counts (<i>p</i> = 0.017), rectal temperature (<i>p</i> = 0.009), and respiratory rate (<i>p</i> < 0.001). Increasing LDP cubically affected superoxide dismutase activity in blood plasma (<i>p</i> = 0.012) and total antioxidant capacity in both blood and seminal plasma (<i>p</i> < 0.001 and <i>p</i> = 0.006, respectively). The optimal response was observed at 30 and 80 mg proline/kg DM for blood and seminal plasma, respectively. With regards to homeostasis indexes, increments in LDP cubically modified blood plasma concentrations of total protein (<i>p</i> = 0.002) and albumin (<i>p</i> < 0.001), with an optimal response found at 70 mg proline/kg DM. A linear relationship (<i>p</i> = 0.005) was also observed between LDP and blood plasma glucose concentrations, with the optimal response being found at 100 mg proline/kg DM. Increasing LDP also showed positive effects on reproductive traits, with quadratic increases in blood plasma testosterone and cortisol concentrations (<i>p</i> < 0.001; optimal responses at 50 and 60 mg proline/kg DM, respectively), a positive linear relationship with in libido, ejaculate volume, sperm concentration and total sperm count (<i>p</i> < 0.001 for all; optimal responses observed at 100 mg proline/kg DM) and a quadratic increase in total functional sperm fraction (<i>p</i> < 0.001; optimal response at 70 mg proline mg/kg DM). Hence, the optimal positive effects of dietary proline supplementation on redox status, blood metabolites, and reproductive traits of rabbit bucks may be achieved at 50–100 mg/kg DM.