Heterosis in egg production in different parts of the laying period of layers of Rhode Island Red origin selected by RRS selection in two environments Part I. Heterosis in egg production in the original populations after few generations of RRS selection

Abstract

Heterosis in hen day egg production was studied in four independent 90 day part periods of the 360 day laying cycle. All parental purebred and their reciprocal crossbred progeny were housed 2 and 4 hens per cage. The parental strains were Rhode Island competitive commercial populations selected by RRS since few generations only. From each pure strain 9 random selected unrelated cocks mated to 15 unrelated pullets produced the purebred and crossbred progeny. The experiment was conducted as an orthogonal randomised factorial trial, sires were regarded as random, mating system (cross vs. pure) and density (2 vs. 4 hens/cage) as fixed effects. A total of 18 paternal half-sib groups of 64 birds each completed the trial. Heterosis was significant (P<0.001) in all part periods in both environments. The heterosis in hen day egg production during the part periods 1-90, 91-180, 181-270 and 271-360 days in production respectively were: 2 birds per cage: 4.75, 4.99, 6.12 and 4.58 eggs, 4 birds per cage: 4.12, 3.14, 5.24, 7.96 eggs. In both environments the mean heterosis across production periods in eggs produced was the same: 5.11 eggs. The relative (%) magnitude of heterosis tended to increase in the second part of the egg production period, this tendency was more pronounced when 4 hens were kept to a cage, simulating a production environment which is very close to that practised on intensive commercial farms. The increased stocking rate depressed egg production significantly (P<0.01-0.001) only in the second part of the laying cycle, interactions mating . density were not significant.