Evaluation of the performance of the Kenya Dual Purpose Goat composites: Additive and non-additive genetic parameters
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Growth data from 6800 progeny of straightbreds, intermediate crosses and the resulting Kenya Dual Purpose Goat (KDPG) composites from 1982 to 2004 were used to estimate additive and non-additive genetic parameters. The KDPG was developed by crossing Toggenburg (T), Anglo-Nubian (N), Small East African (E) and Galla (G) breeds in equal proportions. All parameters were simultaneously estimated for early growth traits by fitting an animal model using Derivative-Free-Restricted Maximum Likelihood (DFREML) procedures (Meyer, 1998). The model included sex, type of birth, period and season of birth, and age of dam classes as fixed effects; crossbreeding parameters were fitted as covariates. Relative to Small East African breed, Anglo-Nubian showed the highest breed effects for weaning weight (+1.69 kg), yearling weight (+1.74 kg) and pre-weaning average daily gains (+13.28 g/day). Between the indigenous breeds, breed differences were in favour of Galla breed except for yearling weight. Individual heterosis had a positive effect on birth weight (+0.05 kg), yearling weight (+0.36 kg) and post-weaning average daily gains (+3.04 g/day) but negative in pre-weaning traits. Maternal heterosis was favourable in the traits influenced by pre-weaning maternal environment (weaning weight and pre-weaning average daily gains). The effect of recombination was negative and, therefore, reduced performance in all traits. Heritability estimates were low with very narrow range between traits. These estimates were 0.13 ± 0.03, 0.16 ± 0.01 0.16 ± 0.04, 0.24 ± 0.01 and 0.10 ± 0.02 for birth weight, weaning weight, yearling weight, pre-weaning and post-weaning average daily gains, respectively. The study shows that the developed KDPG composites have not optimized on the positive dominance effects; an effect due to retained recombination loss caused by lack of selection during breed development. It was concluded therefore, that the KDPG composites are still segregating and have not stabilized into a new breed as was the aim of the breeding programme.