Impact of growth curve and dietary energy-to-protein ratio of broiler breeders on egg quality and egg composition

Egg characteristics have an impact on embryonic development and post-hatch performance of broilers. The impact of growth curve (GC) and dietary energy-to-protein ratio of broiler breeder hens on egg char-acteristics was investigated. At hatch, 1,536 pullets were randomly allotted to 24 pens in a 2 x 4 factorial dose-response design with 2 GC (standard growth curve = SGC or elevated growth curve = EGC (+ 15%)) and 4 diets, differing in energy-to-protein ratio (defined as 96%, 100%, 104% and 108% AMEn diet). Feed allocation per treatment was adapted weekly to achieve the targeted GC and to achieve pair-gain of breeders within each GC. Breeders on an EGC produced larger eggs (delta = 2.3 g; P < 0.001) compared to breeders on a SGC. An exponential regression curve, with age (wk) of the breeders, was fitted to describe the impact of GC and dietary energy-to-protein ratio on egg composition. Yolk weight was 0.8 g higher for eggs from EGC breeders than from SGC breeders (a -108.1 * 0.907Age, where a was 22.1 and 22.9 for SGC and EGC, respectively; R-2 = 0.97; P < 0.001). An interaction between GC and dietary energy-to-protein ratio on albu-men weight was observed (P = 0.04). Dietary energy-to-protein ratio did not affect albumen weight in SGC breeders (42.7 -56.2 * 0.934Age; R-2 = 0.89), but for EGC breeders, a higher dietary energy-to-protein ratio resulted in a 0.9 g lower albumen weight from 96% AMEn to 108% AMEn (a -62.9 * 0.926(Age), where a was 43.4, 43.2, 42.8, and 42.5 for 96% AMEn, 100% AMEn, 104% AMEn, and 108% AMEn, respectively; R-2 = 0.86). Albumen DM content decreased linearly with an increased dietary energy-to-protein ratio, but this was more profound in EGC breeders (b =-0.03 %/% AMEn) than in SGC breeders (b =-0.01 %/% AMEn; P = 0.03). Overall, it can be concluded that an EGC for breeders led to larger eggs with a more yolk and albumen, whereas dietary energy-to-protein ratio had minor effects on egg composition.