Abstract
Abstract. The study was aimed at elucidating the effect of seasons, namely the early wet (EW), late wet (LW), early dry (ED) and late dry (LD) seasons, on genotype sensitivity, its magnitude and application for selection and management of chickens of Bovan Nera (BN) and ISA Brown (IB) origins. Breeding and hatching records from 1999 to 2008 were collected from CHI (Ajanla) Farms and hatchery records, Ibadan, Nigeria. Cock weight (CW), hen weight (HW), hen-house egg production (HHP), egg weight (EW), fertility of egg set (FES) and pullet day-old chicks (PDC) hatched were examined. ANOVA revealed that there was significant (P < 0.05) genotype × season interaction effect. This interaction was observed between genotypic values when compared between seasons within parameters. Within-season sensitivity parameters indicated that BN was more sensitive than IB in HW and FES for all seasons. In ED and LD seasons, sensitivity values were inconsistent in pattern with output levels of FES, HES and PDC hatched because of interaction between genotypes and seasons. Within the LW season, all sensitivity indices for genotypes were consistent in magnitude with productive and reproductive values. Therefore, a genotype's seasonal sensitivity indices could be utilized for direct antagonistic selection in LW season between genotypes in humid tropics.
Highlights
Every genotype demonstrates a reaction norm to the environment in which it is reared
This means that the seasons were statistically different (P < 0.05), clearly defined and distinguishable
These results reveal that there was no significant difference (P > 0.05) between genotypes in cock weight within seasons, but there was significant difference (P < 0.05) in hen weight between genotypes within the late dry season
Summary
Every genotype demonstrates a reaction norm to the environment in which it is reared. The environment may be different farms, production systems, housing conditions, feeds, seasons, temperature, nutrition, topography or locations that are shared in common by all experimental units under study or in any group. These are usually treated as “treatments” in experimental design. When an environment enhances the expression of a character or trait, it is termed “good”, but when it depresses the expression of the character, it is termed “bad” (Falconer and Mackay, 1996)
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