Genetic Improvement Strategy of Indigenous Cattle Breeds: Effect of Cattle Crossbreeding Program in Production Performances

The aim of the review is to summarize the fragmented production performance information on the effects of cattle crossbreeding in different parts of the globe. Most studies indicated that cattle crossbreeding practices conducted under extensive management system for small scale dairy farms is attractive because the optimum requirement (50-62.5%) of exotic cattle blood level inheritance was maintained. However, most developing countries do not use systematic crossbreeding programme. For example, dairy cattle crossbreeding programme in Ethiopia lacks clear breeding policy regarding the breed type to be used and the level of exotic blood inheritance across different agro-ecology and production system. Heterosis is an essential advantage of crossbreeding and maximum heterosis is realized in the first cross (F1) of distinctly different breeds. The purpose of crossbreeding in beef cattle is partly to combine breed differences and partly to make use of heterosis to improve production. Heterosis is highest in F1 generation compared to F2, F3 and F4 crossbred generations. Therefore, terminal crossbreeding is very important in livestock production particularly in beef production. Holstein Friesian dairy cattle produce 40-60% lowered milk yield under tropical and subtropical conditions compared to temperate conditions, and this is due to the exposure of the animals to the different stress factors in the tropical and subtropical conditions. The review also revealed that crossbreeding programme has significant effect in birth weight because all F1 crossbred calves have highest birth weight compared to the purebred calves of Zebu, Sanga and Zenga breeds. Heterosis in a sound crossbreeding program could increase productivity in the beef cow herd by as much as 26% over a comparable straight breeding program. In general, crossbreeding in tropical countries is undertaken to combine superior hardiness, heat tolerance, disease tolerance and/or resistance and environmental adaptability of indigenous cattle with superior milk yield and faster growth rates of exotic temperate breeds. Crossbreeding is one tool to minimize the negative impacts of inbreeding depression in livestock sector. Through crossbreeding there is a chance to have highly productive and adapted breeds. Crossbreeding also affects milk fat and protein compositions of purebred cattle. However, if crossbreeding is indiscriminate and uncontrolled, it may result in poor production performance. Furthermore, a number of studies indicated that indiscriminate and uncontrolled crossbreeding is a major threat to sustainable conservation and utilization of indigenous cattle breeds. Therefore, crossbreeding must be introduced in controlled farms.