Estimates of Breed Additive, Dominance and Recombination Genetic Effects on Growth and Lactation Traits in German Brown x N'Dama Crossbred Cattle under Nigerian Tropical Conditions
I. C. Nwosu *
Department of Animal/Fisheries Science and Management, Faculty of Agriculture and Natural Resources Management, Enugu State University of Science and Technology (ESUT), Enugu, Nigeria.
E. A. Ibeziako
Department of Animal/Fisheries Science and Management, Faculty of Agriculture and Natural Resources Management, Enugu State University of Science and Technology (ESUT), Enugu, Nigeria.
*Author to whom correspondence should be addressed.
Abstract
Crossbreeding indigenous cattle like N'Dama with exotic breeds such as German Brown (Brown Swiss) improves productivity by combining adaptability and performance traits, though understanding additive, dominance, and recombination effects is essential for optimizing breeding strategies.The aim of this study was to evaluate the breed additive, dominances and recombination genetic effects on indigenous N'dama and its crosses with German Brown dairy cows at the University of Ibadan Teaching and Research farm. Overall, 1200 pure German Brown, N'dama and crossbred dairy cattle performance records were used for the study. Data comprised purebred and crossbred genotypes with varying proportions of parental breeds under a structured mating design. Traits analyzed included birth weight (BW), 12-month weight (12-MoWT), average daily gain (ADG), milk yield (MY), and lactation length (LL). Fixed effects of sex of calf, year, season and parity were accounted for using a general linear model (GLM) with least squares procedures to adjust for environmental and management influences. The crossbreeding genetic parameters were estimated following the two-way crossbreeding model of Dickerson (1969). The results showed that additive effect was positive and significant across all traits with highest effects on milk yield (1018.89 kg; 68 83% of the mean) and lactation length (+169.58 days: 64.91% of the mean) and lowest effect on average daily gain (+30g; +10.15% of the mean) and 12-month weight. On the other hand, dominance effect was highest on average daily gain (+150g: +50.73% of the mean) and 12-month weight (+150g: +50.73% of the mean) and lowest on milk yield (-339.59 kg; -22.93%) and lactation length (-89 days: -34.07% of the mean); additive and heterotic reversal effects between growth and production traits. Recombination was negative and positive in all traits, the highest on birth weight (-1.83 kg; -8.05% of the mean) and lowest on milk yield (-20.09kg: -1.36% of the mean), indicating loss of favorable gene combinations in advanced generations. The finding highlights the predominance of additive genetic effects, the importance of heterosis for growth traits, and the detrimental impact of recombination on both growth and production traits. These findings support the use of structured crossbreeding systems that maintain optimal heterozygosity for sustainable cattle improvement in tropical environments.
Keywords: Crossbreeding, additive effects, dominance effects, N'Dama crossbred cattle, tropical conditions