INTRODUCTION HETEROSIS, the increase in performance of crosses over parental strains, has generally been found in fowl for chick livability, early growth rate, age at sexual maturity, egg production and at times for adult livability. Degree of heterosis seems to be positively associated with genetic diversity of the parental strains. A full diallel crossing experiment involving 3 White Leghorn (WL) and 3 Rhode Island Red (RIR) “closed flock” strains has been analyzed and reported by Wearden et al. (1965) with particular emphasis on estimating the relative importance of general and specific combining ability and maternal effects. This follow-up study attempts to elucidate the components of specific combining ability. EXPERIMENTAL Samples of 3 WL and 3 RIR “closed flock” strains were obtained from leading commercial breeders in 1956. They were crossed in a full diallel pattern during the following two years. Two “shifts” of males and approximately 90 females per strain . . .

THE interior and shell quality of eggs laid by the domestic chicken are influenced by the age and strain of bird as well as season. The literature concerning the nature of these relationships has been reviewed by Johnson and Merritt (1955), Funk et al. (1958), Cunningham et al. (1960), Taylor (1960) and Bornstein and Lipstein (1962). The information presented here is meant to supplement information concerning the initial quality of eggs laid by birds of different ages and strains.

RECENT reports (Cunningham et al, 1960; Marion et al., 1964, 1965; Kline et al., 1965) contain reviews of research dealing with the influence of breeding and/or age of laying hens on egg size and the relative proportions of shell, yolk and albumen in eggs. Generally, these reports support the conclusion that egg size can be controlled by breeding, in addition to being influenced by age of the laying hen. Proportions of egg components appear to be amendable by selective breeding, but are greatly influenced by layer age. The percentages of shell and albumen decrease during the first year of lay with an accompanying increase in yolk percentage. The influence of breeding on the chemical composition of egg contents has also been studied. Protein and moisture levels of eggs were shown to differ in different stocks of layers (Cotterill and Winter, 1954; May and Stadelman, 1960). Lipid and fatty acid …

IN THE female fowl, selection for early sexual maturity can easily be practiced, if desired. Since the hormonal mechanisms for spermatogenesis and oogenesis are basically the same, a positive correlation between age at first egg in the female and age at first sperm production in the male, might be expected. Grosse and Craig (1960) found these two traits to be significantly correlated in a study involving two breeds, with four strains per breed. Large differences in the age at which males attain sexual maturity have been reported in the literature (Hogue and Schnetzler, 1937; Parker et al., 1942; Grosse and Craig, 1960) and are, in part, due to differences among breeds, strains within a breed and methods of measurement. The present study was conducted to determine if selection for high and low mating ability had any influence on male sexual maturity and to obtain additional estimates of the age…

THE diallel cross has become a common method of analyzing intra-specific genetic variability among crosses (partial diallel) or among parental subpopulations and their crosses (full diallel). The breeder needs the full diallel to determine whether crossing per se is of value in improving productivity. He needs further to determine the relative importance of certain kinds of specific combining ability, to indicate whether extensive crossing is needed to exploit nonadditive genetic variation. A diallel analysis that allows estimation of maternal effects is needed to determine whether reciprocal crosses are likely to be equivalent. This study estimates the relative importance of general and specific combining ability and maternal influence in strain and breed crosses for certain economic traits in pullets. Experimental Stock. Samples of three White Leghorn (W.L.) and three Rhode Island Red (R.I.R.) “closed-flock” strains were obtained from leading commercial breeders in 1956 and crossed in all…

MORTALITY among breeder males held in confinement is often quite significant, especially so as they approach maturity. Many extra birds have to be kept to insure that an adequate number of breeders will be available. Housing males in individual cages would seem to be the most efficient means of reducing mortality, however, this is not always possible.

INVESTIGATIONS concerning the relationship of egg weight and subsequent performance of broilers to various ages have led to conflicting reports. O’Neil (1950), working with Barred Plymouth Rocks, concluded that those chicks hatching with the highest percentage of the original weight of the egg are heavier at eight weeks of age, more efficient in feed consumption and have a lower rate of mortality. Wiley (1950) likewise concluded that a positive trend in body weight and livability existed in favor of birds from large eggs. Although this trend was not statistically significant, he did find significant differences in feed conversion in favor of birds hatched from larger eggs. Any advantage in favor of birds from large eggs was usually overcome by twelve weeks of age as evidenced by the reduction in magnitude of the correlations between egg size and chick weight from 3–12 weeks of age. That chicks from large…

EVIDENCE for the heritable nature of aggressiveness within strains of chickens has been published by Guhl et al. (1960), Komai et al. (1959) and by Siegel (1960). Tindell and Craig (1960) found differences among sire families in aggressiveness, indicating genetic variability to be present.

EVIDENCE has been accumulated by Guhl, Craig and Mueller (1960) and by Komai, Craig and Wearden (1959) indicating that social aggressiveness within strains of chickens is heritable.

INTRODUCTION THE existence of social organization within flocks of chickens has been known since Schjelderup-Ebbe's (1922) investigations. Sanctuary (1932) reported that hens high in social rank tended to produce more eggs than those low in the "peck-order." Intra-strain competition effects have also been shown by Masure and Allee (1934), Collias (1944), and Guhl (1953) and have led to detailed studies of social status and productivity items for hens. Potter (1949) found that there were differences in social dominance among birds of seven different breeds. Potter and Allee (1953) found that a hen may respond to a member of another breed on the basis of breed rather than individual recognition. Holabird (1955) also observed breed differences in aggressive behavior. The present investigation includes observations and measurements on 288 pullets from 150 to 480 days of age in the first year and 288 pullets from 165 to 270 days of age in …