Statistical Genetics of Competition in Growing Chickens

Abstract

The experiment was designed to obtain the information on breed differences in competitive ability of growing chicks.Total 120 one-week old birds of each sex derived from White Leghorn (W. L.), Rhode Island Red (R. I. R.) and Barred Plymouth Rock (B. P. R.), each comprising 40, birds, were used to construct a single-breed group of 30 birds for each breed and a mixed-breed group of three breeds, each consisting of 10 birds, as an experimental unit with two replications. All birds were restrictively fed with free drinking water. Under this condition the birds were reared for five weeks and weighed weekly.Competitive ability, Cbj, of the jth breed was estimated from the following equation: Cbj=(Y...+2aY2j.-2Y2..-aY.j.)/a, where Yij. denotes the average body weight of the jth breed in the ith group (i=1 for single-breed group and 2 for mixed-breed group, and j=1, 2, ..., a).The results indicated that the inter-breed competition was detected after five weeks of age in males and one week later in females. The B. P. R. had the highest competitive ability and the R. I. R. the lowest for both sexes. The fact that the R. I. R., the heaviest breed of the three, had the lowest competitive ability and the B. P. R., the intermediate size, was superior in competition to the other two breeds suggests that the relationship between body weight and competitive ability of the breed is not so tight as one may expect.Nevertheless, the heavier birds of a breed might have advantages on growth than the lighters of the breed in a mixed-breed group where competition occurred among the breeds. The probable reason was discussed in some details.It was postulated that the interaction between inter-breed and intra-breed competitive abilities would exist when these two competitions occurred in a mixed-breed group.