SCANDINAVIAN SELECTION AND CROSSBREEDING EXPERIMENT WITH LAYING HENS .5. SPECIALIZED COMPARED WITH INDEX SELECTION FOR 2 GENETICALLY ANTAGONISTIC TRAITS IN LAYING HENS

Egg number (EN42) and egg weight (EW42) in the period between age at first egg and 42 weeks of age (P1) were used as the criteria of selection for ten generations in two specialised lines. Two other lines were selected for an index of egg number and egg weight for four generations, and thereafter these two lines were combined with egg mass in P1 (EM42) as the criterion of selection. A random mated control population was also kept throughout the experimental period. Selection for EN42, EW42 and EM42 resulted in a direct cumulative response in generation 10 of about 30 eggs, 16 g of egg weight and more than 1000 g of egg mass in the respective lines in Pl. Correlated results in the residual period were generally in good agreement with expectations. Crosses of the two specialised lines were compared with index/egg mass line, and it was concluded that there is an optimum value for the number of generations that the process of crossing the specialised lines is worthwhile, i.e. generation six in our experiment. The changes in the heritability of the various traits were generally in good agreement with theoretical expectations.