Body weight and/or fatness as potential determinants of the onset of egg production in broiler breeder hens.

In four trials during consecutive years individually-caged birds were weighed at first egg, and in the first two trials they were then killed to determine abdominal and skin fat, in order to establish whether there is a minimal body weight and/or body fat pool required for the start of egg production in broiler breeder hens. There were negative correlations ranging from significant to negligible between body weight and age at first egg. For birds of the same strain on a conventional food restriction regimen, the average weight range at first egg in the four trials was 3.3 to 3.7 kg, which may be a strain characteristic. In spite of severe food restriction, all birds were very fat at first egg. The correlations between fat concentration and age at first egg were negative. In mature pullets a minimum concentration of stored, easily mobilised fat may be essential for yolk formation and ovulation.