Genetic parameters and correlations between growth traits and packed cell volume of N'Dama cattle in the Gambia

The evolution of body weight under the natural trypanosome challenge and its association with disease tolerance to trypanosomosis is of utmost economic importance in cattle. This study estimated heritability for growth traits and packed cell volume (PCV) and their genetic correlations in the N'Dama cattle in the Gambia. A total of 2,488, 2,442, 1,471, 1,934, and 1,452 bodyweight records at 12 months (WT12), 16 months (WT16), 18 months (WT18), 24 months (WT24), 36 months (WT36) and 50 months (WT50) and 1,782, 1,800, 1,844, 1,608, and 1,459 records for PCV at 12 months (PCV12) 18 months (PCV18), 24 months (PCV24), 36 months (PCV36), and 50 months (PCV50), respectively, were analysed. Genetic parameters were estimated using univariate and multivariate animal models using the GIBBSF90 software. Least square means for WT12, WT18, WT24, WT36 and WT50 were 75.08 ± 0.37 kg, 95.58 ± 0.52, 123.80 ± 0.52 kg, 149.90 ± 0.73 kg and 190.37 ± 0.68 kg, respectively. The Least square means for PCV declined from 24.56 ± 0.18 at 12 months of age to 23.18 ± 0.19 at 50 months. Heritability estimates for growth ranged from 0.47 ± 0.05 at 12 months to 0.31 ± 0.06 at 50 months, while for PCV the estimates were 0.09 ± 0.01 to 0.15 ± 0.01. Genetic correlations between bodyweights were high and positive (0.73 ± 0.01 to 0.96 ± 0.01) while those between PCV traits were low to medium and positive (0.16 ± 0.04 to 0.56 ± 0.02). Genetic correlations between bodyweight and PCV range from -0.14 ± 0.02 to 0.59 ± 0.02. BW18 and PCV18 had high heritability estimates and as well as the highest genetic correlation and therefore could be used as selection criteria for body weight and trypanotolerance, respectively.