Associations of major histocompatibility complex haplotypes with body weight and egg production traits in S1 White Leghorn chickens.

Body weights at 8, 20, and 32 wk, total egg production, average egg weight, egg production during a 4-wk period, and age at first egg laid were measured in 652 female progeny of heterozygous x heterozygous (F1) or heterozygous x homozygous (backcross) matings of the Iowa State University S1 White Leghorn chicken line. Hens were classified by B-haplotypes (B1 or B19) and haplotype-associated immune responses (high or low) to the amino acid polymer glutamic acid-alanine-tyrosine (Ir-GAT). Body weights were affected by parental mating group, sire, and dam, but they were not affected by haplotype (B/Ir-GAT). Sexual maturity and egg production were not affected by any factors except hatch. Average egg weight was affected by parental mating group, sire, dam, and genotype, with homozygous B19B19 birds having a heavier mean egg weight (41.71 g +/- .20) than homozygous B1B1 Ir-GAT-high and - low birds (40.8 g +/- .38 and 39.2 g +/- .54, respectively); mean egg weights of heterozygous birds were approximately intermediate to the others.