title: Influence of season of birth on growth and reproductive development of Brahman bulls.
abstract: Seasonal effects on reproduction are more dramatic in Bos indicus than Bos taurus cattle. This experiment evaluated reproductive development of fall- (n=7) versus spring- (n = 10) born Brahman bulls to determine if season of birth affects reproductive development. Measurements of growth and reproductive development began after weaning and continued at bi-weekly intervals until each bull reached sexual maturity. Different stages of sexual development were classified according to characteristics of the ejaculate and included first sperm in the ejaculate, puberty (> 50 x 10(6) sperm/ejaculate), and sexual maturity (two ejaculates with > 500 = 10(6) sperm/ejaculate). Average daily increases in all measured traits were similar in fall- and spring-born bulls and there were no differences in age, body weight, scrotal circumference, or paired testis volume between groups at first sperm or puberty. However, fall-born bulls were older (P < 0.05) than spring-born bulls at sexual maturity (553 days versus 481 days, respectively) as the interval between puberty and sexual maturity was longer (P < 0.05) in fall- than in spring-born bulls (82 days versus 54 days, respectively). The prolonged interval between puberty and sexual maturity in fall-born calves coincided with a short photoperiod (winter) whereas the short interval between puberty and sexual maturity in spring-born calves coincided with a long photoperiod (summer). In conclusion, season of birth affected sexual development; photoperiod might be involved in regulating testicular function immediately after puberty in Brahman bulls.
authors.affiliation: Texas A&M University Agricultural Research and Extension Center, P.O. Box 200, Overton, TX 75684, USA.
authors.forename: Shawn R
authors.initials: SR
authors.lastname: Tatman
authors.forename: Don A
authors.initials: DA
authors.lastname: Neuendorff
authors.forename: Timothy W
authors.initials: TW
authors.lastname: Wilson
authors.forename: Ronald D
authors.initials: RD
authors.lastname: Randel
mesh_terms: D000375:Aging; D000818:Animals; D002417:Cattle / Q000254:growth & development*; D008297:Male; D017440:Photoperiod; D012098:Reproduction; D012611:Scrotum / Q000254:growth & development; D012621:Seasons; D012661:Semen / Q000166:cytology; D012741:Sexual Maturation; D013076:Sperm Count; D013737:Testis / Q000254:growth & development