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

Abstract

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 characteristics was investigated. At hatch, 1,536 pullets were randomly allotted to 24 pens in a 2 × 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% AME_n 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 (∆ = 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*0.907^Age, where a was 22.1 and 22.9 for SGC and EGC, respectively; R² = 0.97; P<0.001). An interaction between GC and dietary energy-to-protein ratio on albumen weight was observed (P = 0.04). Dietary energy-to-protein ratio did not affect albumen weight in SGC breeders (42.7-56.2*0.934^Age; R² = 0.89), but for EGC breeders, a higher dietary energy-to-protein ratio resulted in a 0.9 g lower albumen weight from 96% AME_n to 108% AME_n (a-62.9*0.926^Age, where a was 43.4, 43.2, 42.8, and 42.5 for 96% AME_n, 100% AME_n, 104% AME_n, and 108% AME_n, respectively; R² = 0.86). Albumen DM content decreased linearly with an increased dietary energy-to-protein ratio, but this was more profound in EGC breeders (β = -0.03 %/% AME_n) than in SGC breeders (β = -0.01 %/% AME_n; 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.

Keywords: broiler breeder; egg components; feed strategy; modelling.

Figure 1

Laying rate of broiler breeders fed on 2 different growth curves (SGC = standard growth curve or EGC = elevated growth curve (+15%)) from 0 to 60 wk of age. ^a,bLSmeans within age lacking a common superscript differ (P ≤ 0.05).

Figure 2

Laying rate of broiler breeders fed 4 diets, differing in energy-to-protein ratio (96, 100, 104, or 108% AME_n), fed from 0 to 60 wk of age. *LSmeans within age with asterisk show a significant linear effect of energy-to-protein ratio (P ≤ 0.05).

Figure 3

Egg weight of broiler breeders fed on 2 different growth curves (SGC = standard growth curve or EGC = elevated growth curve (+15%)) and 2 diets, differing in energy-to-protein ratio (96 or 108% AME_n), from 0 to 60 wk of age. ^†∆*LSmeans within age with a dagger (GC × diet (linear)), with a triangle (GC) or with an asterisk (diet (linear)) showed a significant effect (P ≤ 0.05). Data on the 2 intermediate diets (100% or 104% AME_n) is not presented, as effects of dietary energy-to-protein ratio were linearly.

Figure 4

Observed (symbols) and predicted (lines) albumen weight of broiler breeders fed on a standard growth curve (black symbols, dashed line) and 4 diets, differing in energy-to-protein ratio; 96% AME_n (○), 100% AME_n ($\times$), 104% AME_n (∆), or 108% AME_n (◊) or fed on an elevated growth curve (+15% compared to standard, solid lines) and 4 diets, differing in energy-to-protein ratio; 96% AME_n (red ○), 100% AME_n (gray $\times$), 104% AME_n (blue ∆), or 108% AME_n (green ◊), from 0 to 60 wk of age. Each symbol represents 1 replicate at each time point.

Figure 5

Observed (symbols) and predicted (lines) yolk weight (A) and shell weight (B) of broiler breeders fed on 2 different growth curves; standard growth curve (red ○, dashed line) or elevated growth curve (+15%; black $\times$, solid line) from 0 to 60 wk of age. Each symbol represents 1 replicate at each time point.