Examination of the physical characteristics in a diverse group of dwarf White Leghorn pullets before and after first oviposition.

The purpose of the present experiment was to measure changes in physical variables with sexual maturity (SM), the oviposition of first egg, in sex-linked dwarf pullets when SM was delayed by the photoschedule. Offspring were produced from matings of dwarf Single Comb White Leghorn chickens divergently selected for high (H) or low (L) 20-wk BW. At 15 wk of age, pullets from half-sibling sets were randomly assigned to a diet either of low energy (LE: 2,500 kcal/kg of ME, 15% CP) or high energy (HE: 3,000 kcal/kg of ME, 15% CP) and were placed in cages. When a pullet reached SM, the mature (M) pullet and an immature (I, absence of oviposition), half-sibling pullet on the same diet were sampled for BW as well as for the weights of abdominal fat, liver, ovary, oviduct, whole egg (M pullets), yolk, and shell and for the number of rapidly developing follicles. Proximate measurements (wet weight) were made for defeathered carcasses and livers as well as for ovaries and oviducts. There were significant (P less than or equal to .01) line effects for BW at SM (H greater than L); age at SM (L greater than H); weights for the liver, abdominal fat, egg, albumen, shell (H greater than L), and yolk (L greater than H); number of developing follicles (H greater than L); percentage of carcass protein (L greater than H) and of fat (H greater than L); as well as for liver protein (L greater than H), fat (H greater than L), and ash (L greater than H). There were significant (P less than .01) diet effects for abdominal fat (HE greater than LE) and shell weight (LE greater than HE). There was a line-by-diet interaction for total feed intake and for total energy intake from 15 wk to oviposition of the first egg. There were significant (P less than .01) SM effects (M greater than I) for BW at SM, number of developing follicles, oviduct weight, and fat content of the reproductive organs; also, reproductive organ weights accounted for differences in BW at SM. There was an interaction for line by maturity state; the L pullets showed a greater increase in ovarian weight with oviposition of the first egg than did the H pullets. The results of this study indicated that the threshold requirements for BW, composition, or both, for SM may have been exceeded in Leghorn-type chickens when photoscheduling was used to delay the onset of SM.