Oviposition time, flock age, and egg position in clutch in relation to brown eggshell color in laying hens

In Australia and other parts of the world, table eggs with uniform brown eggshell color are well regarded by consumers. Brown eggshell color has been positively correlated with certain egg characteristics such as shell strength and egg specific gravity, along with specific antibacterial functions. In the current study, the effect of hen oviposition time, flock age, and egg position in-clutch on the intensity of brown eggshell color was studied in commercial laying hens. The collected eggs were processed to measure egg weight, shell reflectivity, shell color (L*a*b*), quantification of protoporphyrin IX (PP IX), and shell thickness. Hen oviposition time had a statistically significant effect (P < 0.05) on egg weight, L*a*b*, amount of PP IX, and shell thickness. L* increased from 59.72 in the first half hour after lights on to 61.67 6 hours later, and PP IX per gram of eggshell decreased from 1.32×10(-7) mM to 1.26×10(-7) mM. Flock age had a significant effect on egg weight, L*a*b*, shell reflectivity, PP IX, and shell thickness. The mean egg weight increased from 55.4 g at 25 wk of flock age to 63.3 g at 75 wk of flock age. PP IX per gram of eggshell was 1.45×10(-7) mM at 25 wk and declined to 1.31×10(-7) mM at 75 wk of flock age. Individual hen clutch length was highly variable, ranging from 22 to 123 eggs in a single clutch. Egg position in a clutch had a significant effect on all egg quality variables measured; however, the R(2) values for each variable measured were low. The eggshell color declined to a greater extent with increasing position in a clutch for long clutches compared with short and medium clutches. In conclusion, hen oviposition time affected brown eggshell color with darker brown eggs laid early in the d and lighter colored brown eggs laid later in the morning. The intensity of brown color decreased with flock age, and egg position in-clutch had relatively little effect on brown eggshell color.