Application of some biometrical correlates in the determination of optimum breeding age in the West African Dwarf Buck

Abstract

The optimum breeding age of West African dwarf (WAD) bucks was investigated using biometrical correlates. The study involved 450 semi-intensively raised WAD bucks of 1-15 months old and divided into 15 equal groups. Six bucks were randomly selected per group and were electro-ejaculated to evaluate spermatozoa motility and livability, using standard methods. Testicular volume was determined ultrasonographically using Prilate ellipsoid formula (PEF), Prolate Spheroid Formula (PSF) and Lambert Formula (LF). These were contrasted with testicular volume obtained by the conventional Water Displacement Method (WDM) using testes harvested from the bucks in each group. Data were analysed using descriptive statistics, Pearson correlation and ANOVA at P<0.05. The body weight (r=0.9) and scrotal circumference (r=0.8) correlated significantly with age. The body weights significantly increased from 3.4±0.1 kg at one month to 13.6±0.1 kg at 15 months. The scrotal circumference significantly increased from 7.9±0.1 cm at one month to 17.6±0.2cm 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 normal spermatozoa motility and livability increased significantly from 85+4.0% and 88+3.7% at 6 months to 93+5.0% and 93+4.6%, respectively at 8 months. The PEF, PSF, LF and WDM significantly increased from 16.1+0.1, 23.6+1.7, 22.0+0.1 and 16.2+0.1 cm³, respectively at one month to 28.3+0.2, 40.0+0.3, 38.6+0.3 and 28.5+0.3cm³, respectively at eight months. Comparison of testicular volume procedures showed that PEF did not significantly differ from WDM. An optimum breeding age of 8 months in semi-intensively raised West African Dwarf bucks was established. Ultrasonographic evaluation of testicular volume using the PEF with an average value of  28.3+0.2cm³ is a valuable non-invasive method for the determination of optimum breeding age in West African dwarf bucks.

Keywords: Biometrical correlates, Optimum breeding age, Testicular ultrasonography West African dwarf bucks