Genetic Improvement Strategy of Indigenous Cattle Breeds: Effect of Cattle Crossbreeding Program on Their Reproductive Performances

The aim of the review is to summarize the fragmented information on the effects of cattle crossbreeding on reproductive performance of cattle in different parts of the globe. The performance of animals depends not only on their genetic merit but also on other factors such as feeding, health management and other environmental factors. All breeds have strong and weak traits; there is no single best breed in all traits. Crossbreeding native cattle of Bosindicus type and exotic Bostaurus cattle is now a widely used method of improving reproduction of cattle in the tropics and subtropics. Crossbreeding is the reverse of inbreeding and is economically important practice in livestock breeding. Crossbreeding is an attractive option for livestock genetic improvement because of the quick outputs obtained. Crossbreeding is a crucial genetic improvement option for the lowly heritable traits of animals such as fertility of cows. Crossbreeding programme should respect the principle of “the right animal in the right place”. Under extensive management system of the tropics and subtropics, exotic cattle blood level inheritance should be from 50-62.5% for a maximum reproductive efficiency. Reproductive efficiency is a determinant factor for dairy and beef production efficiencies.Crossbreeding of highly productive and adapted breeds can improve overall performance. Heterosis is highest in F1 generation than in F2, F3 and F4 crossbred generations because the heterosis level is halved in each of the subsequent generations. Backcrossing reduces heterosis effects and thus reduces the advantages obtained from heterosis. However, it should be emphasized that heterosis cannot improve all traits, for example,carcass traits such as rib-eye area, marbling and meat tenderness. Calving interval affects total milk production of the dairy herd and the number of calves born, and is the most important index of reproductive performance.