A genetic study of crooked toes and crooked keels in chickens

The objectives of this study were to estimate for the skeletal deformities of crooked toes and crooked keels in chickens: (1) the sire and dam effects, (2) the heritability and (3) genetic and phenotypic correlations.

Data were collected from measurements of crooked toes and crooked keels on 1316 offspring, at 98 days of age, from matings of 19 sires and 168 dams of Single Comb White Leghorns. The analyses of variance were based on half-sib and full-sib analyses of both crooked toes and crooked keels scores within each sex, and all data adjusted for sex. The components of variance and covariance due to sire and dam in the model were used to calculate estimates of heritability and genetic and phenotypic correlations.

It was observed that sex has a significant (P < 0.001) effect on the incidence of both crooked toes and crooked keels with males having a greater incidence of crooked toes and crooked keels than females.

The analysis of half-sib data showed significant differences (P < 0.001 for male progeny and P < 0.05 for female progeny) among sires with respect to the occurrence of crooked toes and crooked keels.

The analysis of variance of the full-sib data adjusted for sex showed significant differences (P < 0.001) among sires with respect to type of deformities. Also significant differences (P < 0.01) among dams with respect to the incidence of crooked toes score and a significant difference (P < 0.05) among dams with respect to keel deformity.

In the full-sib analysis, male progeny showed significant differences (P < 0.001) among sires, while the differences among dams were significant (P < 0.01) with respect to crooked toes score, and crooked keels score (P < 0.05). Differences among sires of female progeny were of low significance (P < 0.05), while differences among dams were not significant (P > 0.05). With respect to keel scores, the differences in female progeny were of low significance (P < 0.05) among both sires and dams.

It was found from the estimates of heritability of crooked toes and crooked keels from half-sib and full-sib analysis adjusted and unadjusted for sex that male progeny gave higher estimates of heritability than females and in most cases the estimates of heritability of keel score were higher than those of toe score.

From the estimates of genetic and phenotypic correlation, it was found that most were very low, indicating that the two diseases are practically independent of each other. The females yielded higher estimates than the males in all cases. The paternal half-sib and full-sib estimates of genetic correlation were higher than other estimates. It is concluded that the genetic effect of the sire on the predisposition to crooked toes and keels of the progeny appears to be greater than that of the dam.