Abstract
The objective of this study was to evaluate genetic and phenotypic parameters for some important economic traits of Black Bengal goats. Genetic parameters were estimated by Residual Maximum Likelihood procedure, fitting an animal model ignoring maternal genetic or permanent environmental effects. Least-squares means for body weights at birth, 3, 6, 9 and 12 months of age were 1.09, 5.12, 8.02, 10.92 and 14.47 kg, respectively. Sex of kid has significant (P<0.05) effect on body weights at 6, 9 and 12 months of age. Type of birth and parity of dam has significant (P<0.01) effect on birth weight only whereas season of birth affected (P<0.05) all the body weight traits. Heritability estimates for body weights at birth, 3, 6, 9 and 12 months of age were 0.45, 0.47, 0.45, 0.49 and 0.47, respectively. Genetic and phenotypic correlations between body weights at different ages were positive and moderate to high in magnitude. Genetic correlations between body weight traits ranged from 0.34 to 0.83, whereas phenotypic correlations ranged from 0.34 to 0.90. The estimates of genetic and phenotypic correlations showed no genetic antagonisms among the weight traits analyzed. The high heritability estimates obtained for body weights indicating that mass selection would generate substantial selection responses at all stages of growth. The effect of parity of doe was significant for litter size at birth (LSB), litter size at weaning (LSW), litter weight at birth (LWB), litter weight at weaning (LWW). In general, LSB, LSW, LWB and LWW increased with the progress of parity. The effect of season of kidding was significant for LSW, LWB and LWW. The least-squares means of LSB, LSW, LWB, LWW and gestation length were 1.50, 1.29, 1.58 kg, 6.37 kg and 144.71 days, respectively. Estimates of heritability for LSB, LSW, LWB, LWW and gestation length were 0.08, 0.13, 0.10, 0.00 and 0.18, respectively. The low estimates of heritability obtained for reproductive traits indicated that selection based on the doe's own performance may result in slow genetic improvement. Least-squares mean for daily milk yield (DMY) was 354.76 gm. DMY was significantly (P<0.01) affected by parity, litter size and season of kidding. The heritability of DMY was low (0.15) and the trait can only be measured on females suggests that Progeny Testing may be the best sire selection method for this trait. The least-squares means of semen volume (ml/ejaculate), sperm concentration (10⁹ cells/ml), mass motility (%), sperm livability (%) and normal spermatozoa (%) were 0.56, 2.55, 79.71, 86.78 and 90.48, respectively. Season of collection and scrotal circumference significantly affected all semen characteristics studied. Age of bucks affected all semen characteristics except mass motility. Body weight had a significant effect on semen volume and mass motility. Heritability estimates were moderate for sperm concentration (0.38) and lower for semen volume, mass motility, sperm livability and normal spermatozoa (0.05 to 0.18). Phenotypic correlations ranged from slightly negative (-0.001) to moderately positive (0.42) and genetic correlations ranged from moderately negative (-0.37) to strongly positive (0.99). Sperm concentration was the only semen trait of Black Bengal goat where reasonable genetic progress may be possible through selection. Selection for increased scrotal circumference should have favourable correlated response in semen characteristics.