Physiological variations in reproductive and metabolic features of white-tailed deer (Odocoileus virginianus) bucks throughout the rutting season.

White-tailed deer farming is a growing industry in the United States, yet there is still a need to improve breeding practices in captive cervids. The objective of this study was to compare reproductive and somatic characteristics of white-tailed bucks early in the breeding season (September), at peak rut (December), and late breeding season (March). We hypothesized that reproductive parameters would improve at the peak of the breeding season. Young, mature bucks (n = 7-11, ages 2-3 yr) were anesthetized via projector with tiletamine-zolazepam and xylazine. Semen was collected by electroejaculation and evaluated for sperm output, motility, and morphology. The bulbourethral, vesicular, and prostate glands were measured by transrectal ultrasound. Body condition score, thoracic circumference, rump fat thickness, scrotal circumference, and testicular measurements were also recorded. Serum testosterone, estradiol, and IGF-I concentrations were measured. Body condition score and rump fat thickness were highest in September, intermediate in December, and lowest in March (p < 0.01), whereas thoracic circumference was lowest in September (p = 0.02). In September, serum IGF-I was highest (p < 0.01) and estradiol was lowest (p ≤ 0.02). Serum testosterone levels were lowest in March and highest in December (p < 0.01). Testicular volume and scrotal circumference were highest in September, intermediate in December, and lowest in March (p < 0.01). Bulbourethral gland length was greatest in March (p ≤ 0.05), whereas prostate length was greatest in September (p ≤ 0.02). Vesicular gland length and width were highest in December, intermediate in September, and lowest in March (p ≤ 0.02). Both overall and progressive sperm motilities were lowest in March (p < 0.01), but did not differ between September and December (p ≥ 0.12). In December, bucks had the highest percentage of normal sperm and lowest percentage of primary sperm defects (p ≤ 0.01). Collectively, our results demonstrated variation in reproductive and metabolic characteristics of white-tailed deer bucks throughout the breeding season at 40°N. The physiological variations described here will be useful for veterinarians and researchers performing reproductive evaluations in white-tailed deer bucks.