The role of hen body weight and diet nutrient density in an extended laying cycle

The egg production (EP), egg quality and health of heavier or lighter hens fed a diet of either higher nutrient density (HND) or lower nutrient density (LND) during early lay, was assessed at very late lay. Based on their body weight (BW) at 18 wk of age (WOA) ISA Brown pullets were allocated as either heavier weight (HW; average 1.65 kg) or lighter weight (LW: average 1.49 kg). Half of each BW group received the HND (2,901 kcal/kg; 17.6% crude protein (CP) or LND (2726 kcal/kg, 16.4% CP) diet from 18 to 24 WOA. From 25 to 90 WOA all birds received identical early, then mid and late-lay diets. Hen BW was measured after peak-lay (36 WOA) and at 90 WOA. At 89 WOA and across 18 to 36 and 18 to 89 WOA feed intake (FI), EP, egg mass (EM), and feed conversion ratio (FCR) were calculated. Eggshell quality, breast score, relative ovary weight and liver and bone health were evaluated in very late lay. Differences in BW continued to 90 WOA. At 36 WOA HW hens produced heavier eggs, and had higher 18 to 36 WOA cumulative FI, EM (P < 0.001) and FCR (P < 0.05). When 89 WOA HW birds consumed more feed (P < 0.001) but EP, EM and FCR did not differ from LW hens. Cumulatively, 18 to 89 WOA FI and EM were higher for HW hens (P < 0.05), but cumulative EP and FCR was not different. The early-lay HND diet improved very late lay eggshell thickness (P < 0.05) and shell breaking strength (P = 0.05). Lighter hens fed HND and HW hens fed LND diet produced heavier eggs, higher relative oviduct weight and lower liver lipid peroxidase in very late lay (P < 0.05). Bone strength did not differ, but LW hens had higher femoral manganese and zinc (P < 0.05), lowering their likelihood of osteoporosis. Overall LW hens sustained EP throughout a longer laying cycle with beneficial bone characteristics. The HND diet improved eggshell strength and, in LW hens reduced hepatic oxidation.