Genetic Evaluation of Trypanotolerant N`Dama Cattle under an Open Nucleus Breeding Programme In the Gambia

Abstract

The N’Dama cattle breed is adapted to survive in tsetse-infested areas and to thrive on poor-quality feeds in West Africa. Despite the importance of the N’Dama cattle in the Gambia, genetic parameters such as heritability estimates, genetic correlations and response to selection for traits in the breeding goal have not been estimated. Therefore, this study aimed to estimate genetic parameters and correlations between growth traits and packed cell volume (PCV), test day milk yield, early growth and fertility traits, and to explore the use of principal component analysis (PCA) to predict multiple trait response to selection for alternative selection indexes of the traits in the breeding goal for N’Dama cattle in the Gambia. Genetic parameters were estimated from univariate and bivariate analyses using the Bayesian procedure implemented in Gibbs sampling in the GIBBS1F90 software. The heritability estimates for body weight at birth, 12 months, 16 months, 24 months, 36 months and 50 months were estimated as 0.30±0.04, 0.51±0.06, 0.47±0.05, 0.39±0.05, 0.36±0.05, 0.22±0.07, 0.31±0.06 and 0.31±0.06, respectively. The respective heritability estimates for PCV were 0.15±0.01, 0.10±0.01, 0.09±0.01, 0.12±0.01, and 0.14±0.3. Genetic correlations between body weight and PCV range from negative and low (-0.14±0.02) to positive and medium (0.59±0.02). The highest genetic correlations were reported for WT18 and PCV18 (0.59±0.02). Direct heritability estimates for BW, WWT, Pre-ADG, Post-ADG, AFC and CI were 0.44±0.04, 0.48±0.03, 0.42±0.03, 0.38±0.03, 0.39±0.01 and 0.14±0.01, respectively, while maternal heritability estimates for BW, WWT and ADG were 0.13±0.03, 0.00±0.00, and 0.19±0.01, respectively. Test-day milk yield had high and positive genetic correlations with early growth traits and CI, ranging from 0.51 to 0.88. The correlation between CI and AFC was 0.80±0.03. CI had negative correlations with early growth traits (-0.01±0.04 to -0.97±0.02). The first three principal components (PC) were associated with eigenvalues greater than 1 and cumulatively explained 70% of the total variation. The expected genetic progress for MY100, pre-ADG, post-ADG, and PCV were positive for the three PCIs as well as CSI. The expected genetic progress for MY100, pre-ADG, post-ADG, and PCV for all SIs ranged from 1.76kg to 4.05kg, 0.01kg to 1.71kg, 0.00 kg to 0.90kg, 0.11% to 0.55%, respectively. CI and AFC reduced by -0.57 to -1.56 months and -0.23 to -1.60 months, respectively. SIPC1 resulted in favourable responses in MY100, CI, AFC, pre-weaning and post-weaning growth rates and PCV and also had the highest overall response. Genetic improvement of pre-ADG, Post-ADG and TDMY in the N’Dama cattle breeding programme is expected to result in precocious AFC and increased CI. Therefore, a multiple trait selection index based on the first principal component (SIPC1) would lead to favourable genetic response in all breeding goal traits.