Sexual Differences in Calcification of Chicks and the Effect on Assays

CHICKS display sex differences in such factors as growth rate and feeding efficiency. Consequently, the proper interpretation of the results of feeding trials involving chick populations of mixed sexes requires that due consideration be given to the distribution of sex in each test lot. For this reason the established procedure of reporting results of chick feeding experiments conducted at the Larro Research Farm calls for a separate presentation of the data for males and females. This practice of reporting the sexes separately led several years ago to the discovery that a significant sex difference exists in the rate of calcification. One of these early roentgenographic reports that drew the author’s attention to the sex-difference in ossification of homologous shaft bones—in this case the metatarsus—is presented by Figure 1. Since then many thousands of X-ray photographs have been taken which consistently and conspicuously show a greater degree of calcification . . .