Genetic Effects of Additive, Dominance and Recombination Effects in German Brown × N'Dama Crossbreds for Enhanced Survival and Reproductive Performance under Nigerian Conditions

Abstract

Crossbreeding between indigenous N’Dama and exotic German Brown cattle has been explored to improve reproductive performance and productivity in tropical dairy systems through the combined effects of adaptation, additive genetics, and heterosis.The aim of this study was to estimate 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. A total of 914 pure German Brown, N'dama and crossbred dairy cattle performance records were used for the study.  The traits studied include mortality, calving rate, age at first calving (AFC), and calving interval (CI) from seven genetic groups (purebreds, F1, F2. and advanced backcrosses). 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 show that dominance effects were negative and significant across all traits, with large magnitudes observed for mortality (−19.27; -93.2% of mean) and calving rate (−26.88; -68.02% of mean), suggesting substantial heterosis contributing to reduced mortality and improved fertility performance. On the other hand, additive effects were positive, significant but low, for instance, mortality (+3.70; +17.9% of mean) and calving rate (+6.42; +0.16% of mean), suggesting small incremental effect through within breed selection.  Recombination effects showed breakdown of favourable gene combinations as mortality was +2.88; that is +13.9% of the mean as against -93.2% dominance value, calving rate was -6.30; that is -15.94% of the mean as against -68.02% dominance value. The findings highlight the potential for exploiting dominance in survival and reproductive efficiency traits, while emphasizing the need for careful breeding strategies to manage recombination losses in advanced generations.