Extensive research has investigated the effects of production systems on egg quality; however, confounding problems exist with many of the experimental designs. Insufficient consideration is given to the influence of genotype, hen age, ambient temperature and stress on egg quality. Eliminating the ambiguity created by these effects is crucial when evaluating the effect of production system on egg quality.
The present study aims to identify limits to the hen age, so that age is not a confounding factor when evaluating the effect of different production systems on egg quality.
Material and methods
All eggs were obtained from Isa Brown hens that had been reared on a single farm. During production, the hens were housed in a single barn shed. Hens of different ages were housed in individual units of 2500 birds. Eggs were collected on one single day from hens of four different age groups (21, 30, 50 and 63 weeks). The eggs were stored in a refrigerator at 4°C, in a cool room temperature at 15°C or in a room temperature at 22°C over a 28-day period. Twenty eggs were sampled at the time of collection and then after storage for 7 14, 21 and 28 days. At each sampling time conventional measures of egg quality, egg weight, Haugh unit (HU), albumen index (AI) and yolk index (YI) were made but here the data analysis concentrated on differences in HU. Data were analyzed using the REML linear mixed model function of Genstat® 17th edition.
Results and discussion
The effect of hen age on HU measurements was significant but it was influenced by storage temperature and storage time as the three-way interaction between these was significant (P<0.001).
The HU changes at the lowest (4°C) and highest (22°C) temperature are given in Figure 1. For all flocks the HU significantly decreased between lay and the end of storage (P<0.05). The decline in HU was more pronounced as the storage temperature increased (P< 0.05). At lay, the 50 wk (90.8) and 63 wk (88.6) flocks had similar HU measures and were lower than for the 21 (96.8) and 30 (102.7) wk flocks (SEM 2.32: P < 0.05). At all storage temperatures and times, the HU was similar for the 50 and 63 wk flocks but lower than the younger flocks (P < 0.05).
In conclusion, when evaluating the effect of egg production systems on egg quality, use of Isa Brown hens between at 50 and 63 weeks of age, would eliminate the influence hen age has on such evaluations.
Chung SH & Lee KW (2014) Int. J. Poult. Sci. 13: 634-636
From the Proceedings of the Australian Poultry Science Symposium