Genotype x environment interactions in fowls

Two genetically diverse stocks of fowl (a Norwegian egg-type and an indigenous fowl) were compared for performance from 9 to 38 weeks of age under two programmes of feeding (low versus high) and two systems of management (semi- versus total confinement). The high feeding programme involved commercial growers and layers mash during the periods 9 - 18 weeks and 79 - 38 weeks of age respectively, whereas the low programme involved mixed mash comprising of the above commercial feeds and maize meal in equal proportions. The birds in the total confinement system were kept indoors through-out the experimental period whereas the semi-confinement groups had access to the range during day time. The results revealed that the Norwegian stock excelled over the indigenous stock with respect to most body weight measurements, age at sexual maturity, egg number, egg weight, albumen quality and for yolk standing quality. There were also indications that the two stocks differed considerably with respect to rate of egg production in favour of the Norwegian stock and with respect to body weight at sexual maturity in favour of the indigenous birds. The only trait for which the indigenous birds excelled was the proper lion of yolk in eggs. The difference between programmes of feeding was considerably large only for body weight at 23 weeks of a e, age at sexual maturity, egg number and for egg weight in favour of the high programme. The systems of management however did not differ significantly with respect to any of the traits considered. Few significant interaction effects were demonstrated in this study but there were evidence though faints of the existence of several interactions involving stocks. For example, apart from the significant stock x feeding programme interactions revealed for egg shell thickness and for 23 week body weight, there were other small interaction effects due to stock and feeds with respect to age at sexual maturity, egg number, albumen quality and for proportion of yolk in eggs. For most of these traits the difference between feeding programmes were several fold as large within the Norwegian stock compared to that within the indigenous stock. Other interactions were of stocks with systems of management with respect to body weight at 38 weeks of age and at sexual maturity albumen quality proportion of yolk and egg shell thickness. Of these only that for 38 week body weight was statistically significant. In most of these cases the indigenous birds were favoured by the semi-confinement system of management whereas there was no apparent difference between the two systems within the Norwegian stock. It is concluded from these results that the genetic background was the most important source of variation for nearly all the traits considered in the present study. Feeding programmes had profound effects mainly on early growth and egg productions, but systems of management were relatively unimportant in determining the performance of the birds. Interaction effects though in most cases small, were consistent enough to suggest that they might affect a breeding programme involving stocks similar to those used in the present study. It seems that the indigenous birds were less responsive to better diets than the Norwegian birds were.