Crossbreeding as a tool for genetic improvement of chickens in suboptimum environments.

A 2-phase crossbreeding study was undertaken to explore prospects of improving the performance of chickens under extensive production conditions in Tanzania. The first phase was carried out under reasonably good feeding and housing conditions and involved one imported meat and egg type each as well as a local breed and their crosses. In the second phase, 15 genetic groups with graded proportions of inheritance from the 3 parental breeds were compared for their performance under relatively poor conditions of feeding and general management. The results revealed that under good production conditions the performance in a particular trait increased with increasing levels of inheritance from the exotic breed which had been developed mainly for that trait. Under poor management conditions, the trend was rather obscure, with the superiority of germ plasma from the exotic breeds expressed in the crosses rather than in the parental breeds. The disparity between the results obtained in the two phases is attributed to genotype x environmental interaction, heterosis, heterosis x environment interaction, and maternal and sex-linked influences. It is concluded that the genetic disposition of the high performers should be adapted to the local production conditions by forming synthetic breeds based on crossbreeding.