Egg production efficiency in dwarf lines selected for high and low body weight as influenced by feed restriction

Hens from dwarf Single Comb White Leghorn lines selected for four generations for high (H) and low (L) body weight (BW) plus randombred controls (C), sixty birds per line, were placed in cages at 18 wk of age and randomly assigned to either a full-fed (FF) or restricted-fed (R) (10 percent less than FF group) treatment. Birds received a layer ration having 16% protein and 2,816 kcal/kg metabolizable energy. Water was provided ad libitum. Individual BW and egg weights (EW) were obtained, and daily feed intake (DFI), egg production (EP), performance efficiency (PE) [egg mass (EM) per BW], and feed efficiency (FE) [EM/DFI] were calculated for 28-day periods from 18 to 41 wk of age. There were significant line, treatment, and age effects and line by age interactions for BW, EW, EM, DFI, and PE; FE was significantly influenced by age. There were significant treatment by age interactions for BW, DFI, and FE. Feed intake, BW, and EW were greatest for FFH hens and increased in all lines with age. Maximum EM occurred during 30 to 33 wk for RH and RL hens, during 34 to 37 wk for FFH, and during 38 to 41 wk for FFL. Maximum PE occurred during peak EP. Maximum FE for FFH and FFL occurred during 26 to 29 wk and during 30 to 33 wk for RH and RL. Data for C hens were intermediate to the other lines. Feed efficiency was improved by restriction for L hens from 26 to 33 wk and for H hens from 26 to 33 wk and for H hens from 26 to 41 wk of age.