APPLICATION OF SOME BIOMETRICAL CORRELATES IN THE DETERMINATION OF OPTIMUM BREEDING AGE IN THE WEST AFRICAN DWARF BUCK

Abstract

Sexual maturity of male animals begins at puberty and peaks at the Optimum Breeding Age (OBA), which marks attainment of maximum functionality of the gonads. Despite the high socio-economic importance of goats, the OBA of the West African Dwarf Buck (WADB) is yet to be determined. Therefore, the OBA in the WADB was investigated using biometrical correlates. A field study involving 450 semi-intensively raised WADB was conducted from October, 2012 to October, 2013. The bucks were in 15 equal groups (1-15 months old) for the determination of Body Score (BS), Body Weight (BW) and Scrotal Circumference (SC). Six bucks were randomly selected per group for subsequent studies. The bucks were electroejaculated to evaluate semen volume, normal spermatozoa, spermatozoa motility, livability and concentration, using standard methods. The TV determined ultrasonographically using Prolate Ellipsoid Formula (TVPEF) and Prolate Spheroid Formula (TVPSF) were contrasted with TV obtained by conventional Water Displacement Method (TVWDM). Testicular morphometry [Seminiferous Tubular Diameter (STD) and Germinal Epithelial Height (GEH)] and testosterone profile were evaluated using Motic Images Plus software and ELISA technique, respectively. Data were analysed using descriptive statistics, Pearson correlation and ANOVAat α 0.05. The BS (r = 0.2), BW (r=0.9) and SC (r=0.8) correlated significantly with age. The BW significantly increased from 3.4±0.1 kg at one month to 13.6±0.1 kg at 15 months. The SC significantly increased from 7.9±0.1 cm at one month to 17.6±0.2 cm at 15 months. Azoospermia, first appearance of spermatozoa and best quality semen were observed in the bucks’ ejaculate at 1-5, 6 and 8-15 months, respectively. Spermiogram showed that semen volume, normal spermatozoa, spermatozoa motility, livability and concentration increased significantly from 0.2±0.1 mL, 87±2.7%, 85±4.0%, 88±3.7% and 1.7±0.0 × 109Cells/mL, respectively at six months to 0.3±0.1 ml, 92±3.4%, 93±5.0%, 93±4.6% and 2.1±0.1 × 109Cells/mL, respectively at eight months. The TVPEF, TVPSF and TVWDM significantly increased from 16.1±0.1, 23.6±1.7 and 16.2±0.1cm3, respectively at one month to 28.3±0.2, 40.0±0.3 and 28.5±0.3 cm3, respectively at eight months. Comparison of TV procedures showed that TVPEF did not significantlydiffer from TVWDM, while TVPSF was significantly higher than TVWDM. The STD and GEH significantly increased from 83.1±0.2 µm and 28.4±0.2 µm, respectively at one month to 574.1±0.3µm and 197.5±0.3 µm, respectively at eight months. The testosterone concentrations increased significantlyfrom 0.1±0.0 ng/ml at one month to 4.7±0.2 ng/mL at eight months. In the parameters studied (excluding BW and BS), there were no significant increases from eight months to 15 months. An optimum breeding age of eight months in semi-intensively raised West African Dwarf buckswas established. Ultrasonographic evaluation of testicular volume using the Prolate Ellipsoid Formula is a valuable non-invasive method for the determinationof optimum breeding age in West African Dwarf bucks. Keywords: Biometrical correlates, Optimum breeding age, Testicular ultrasonography, Semi- intensive, WestAfrican DwarfBucks. Word count: 455