DETERMINANTS OF ONSET OF PUBERTY IN WEST AFRICAN DWARF BUCKS RAISED UNDER INTENSIVE MANAGEMENT

Abstract

Production of the West African Dwarf (WAD) goat plays a vital role in the livelihood of rural populations as its sales either as live animal or meat augments household income. The determination of the onset of sexual maturity in male domestic animals, defined by the first appearance of mature spermatozoa in the cauda epididymis is vital in andrological studies. There is a dearth of information on the onset of puberty in WAD bucks raised under intensive management resulting in sub-optimal utilization of theirversed reproductive potential. This study was designed to investigate somatic parameters, testosterone concentration, spermiogram, testicular and epididymal histology as indicators of onset of puberty in WAD bucks raised under intensive management. Sixty WAD kid bucks, obtained from 80 oestrus-synchronised and naturally mated adult WAD does were used for the study. The kids were nursed by the dams till sixth week post-kidding and thereafter fed forage supplemented with concentrate at 500 g/animal/day till end of the experiment. Water was provided ad libitum. Body Weight, Somatic parameters: [(Scrotal Length (SL), Scrotal Circumference (SC), Crown-Rump Length (CRL), Height At Withers (HAW)] and blood sample for serum testosterone were obtained from the bucks weekly (1-18 weeks). Epididymal semen characteristics (sperm motility and concentration), testicular and epididymal histology were investigated weekly (4-18 weeks). Data were analyzed using correlation regression and one-way ANOVA at α 0.05. Body weight and somatic parameters of bucks increased significantly during the first twelve weeks, while no significant increase was observed from weeks 12-18. Age was positively correlated with SL (r = 0.912), SC (r = 0.804), CRL (r = 0.625), HAW (r = 0.691) from 1-12 weeks. Testosterone concentration fluctuated in the first eight weeks of life with a non-significant increase from week 9 - 12. There was a significant increase in testosterone concentration in the bucks between weeks 12 (6.12+0.15) and 13 (10.20 ± 0.68ng/mL). Testosterone concentration peaked at week 14 (11.25 ± 1.75 ng/mL) but thereafter declined till week 18. Sperm motility and concentration significantly increased from 60.50±10.08 to 82.30 ±15.70 % and 89.30 ± 9.20 x 106 to 125.3 ± 16.70 x 106 sperm/mL respectively, between weeks 13 and 14. Canalisation of the seminiferous tubules was absent in the bucks till week 12. The first observation of elongated spermatids in the lumen of seminiferous tubules was at week 12, while mature spermatozoa were first observed in the cauda epididymis at week 13. Epididymal epithelium changed from simple cuboidal (4-12 weeks) to pseudo-stratified columnar (12-18 weeks). Luminal diameter of seminiferous tubule and ductal diameter of epididymis significantly increased between weeks 13 and 14 from 32.73 ± 0.44 to 78.59 ± 9.18μm and 68.52 ± 12.35 to 102.14 ± 23.76 μm, respectively with no significant difference thereafter. Marked changes in somatic parameters, testosterone concentration, epididymal semen characteristics, testicular and epididymal histology were indicative of the onset of puberty which occurred between weeks 13 and 14 post-kidding in West African Dwarf bucks raised under intensive management. This period is therefore recommended as the earliest time for harvesting of semen for andrological purposes.