Survey of line crosses in a brown leghorn flock

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Abstract
A preliminary study of the hatching weight of chicks of two pairs of pure lines and their reciprocal crosses shows that the relationship of net chick weight, excluding yolk sac, to egg weight, is constant for the lines ; although this is not so for an exceptional line selected for small size, but not examined in detail. Chicks from one pair of reciprocal matings are relatively larger than representatives of their parent lines, but those from the other are not. Detailed examination of the amount of egg material used to form the chick shows that two lines which produce the same relative size of chick do so because one line uses more of the egg, but utilises it less efficiently, than the other. Further, the different genotypes take different times to hatch, the hybrids being earlier than their corresponding dam line. There are differences between reciprocals in hatching time and in efficiency of egg utilisation, but they tend to be confounded. There is no evidence of an optimal egg size for relative chick weight either within lines or within hybrid groups.