Asian Journal of Research in Zoology

Genetic architecture of production and reproduction traits in cattle crossbreeding can be understood through additive, dominance, and recombination effects, enabling the development of efficient and climate-resilient breeding strategies such as the Crossbreeding Efficiency Index (CEI) for optimizing productivity and adaptability in tropical systems.The aim of the study was to evaluate the reproductive and productive efficiency of different genetic groups of German brown x N’dama crossbreeding using a Crossbreeding Efficiency Index (CEI). The objective was to identify the optimal level of crossbreeding between N’Dama (indigenous) and German Brown (exotic) cattle for improved performance and adaptability. A total of 2114 records of mortality, productive and reproductive traits from crossbreds and purebred German Brown and N'Dama collected from the crossbreeding programme at the University of Ibadan, Nigeria, between 1970 and 1988 were analysed using General Linear Model (GLM) procedure to obtain least squares means for each genetic group while adjusting for non-genetic fixed effects of sex of calf, season, year of birth, and parity. The traits (mortality, calving rate, age at first calving, calving interval, birth weight, 12-month weight, average daily gain, milk yield, and lactation length) were standardized for comparability for variables measured in different units, then weighted according to their relative importance and aggregated to compute CEI for each genetic group. The results showed clear variation in efficiency among genotypes. The F₁ (½ German Brown × ½ N’Dama) recorded the highest CEI (1.945), followed by ¼ German Brown × ¾ N’Dama (1.875) and F₂ (1.789). The German Brown purebred ranked fourth (1.658), while 5/8 German Brown × 3/8 N’Dama (1.474) and ¾ German Brown × ¼ N’Dama (1.059) showed reduced efficiency. The N’Dama purebred had the lowest CEI (1.000), serving as the baseline. The superior performance of F₁ and  German Brown × N’Dama reflects the balance between productivity and environmental adaptability, while the decline in F₂ and higher-grade exotic crosses indicates recombination loss and reduced fitness under tropical conditions. In conclusion, the study demonstrates that optimal cattle performance in the tropics is achieved in F₁ and German Brown × N’Dama (backcross genotype). These findings highlight the progressive decline in CEI with increasing German Brown inheritance, which suggests the presence of an optimal genetic threshold (50–75% indigenous genes) beyond which adaptability declines faster than productivity increases.