Laying performances, egg composition, and glucose tolerance of genetically lean or fat meat-type breeders.

Genetically fat and lean breeders were compared for laying performance and glucose tolerance. Laying females were fed ad libitum or restricted (85% ad libitum). Ad libitum-fed fat breeder hens (FL) were lighter and produced lighter eggs than lean hens (LL). However, the yolk percentage of the egg and yolk output were higher in FL. Differences in the glucose-insulin balance were consistently observed between lines in females at 203 and 326 days and in males at 203 days of age. The FL birds displayed lower plasma glucose and higher plasma insulin concentrations for a given plasma glucose level. Feed restriction reduced egg output, yolk output, yolk lipids, and plasma insulin levels during glucose tolerance in females at 326 days of age. Therefore, the glucose-insulin imbalance previously described in young FL birds persists in adults. The enhanced propensity of the FL to synthesize and deposit lipids also affects vitellogenesis. Insulin is also implicated in vitellogenesis.