Standardizing comparisons of egg quality from different production systems by identifying confounding influences

Context. When investigating production system effects on egg quality, it is crucial to eliminate confounding influences of genotype, nutrition, management, hen age, ambient temperature, and stress. Aims: Determine effects of acute stress, hen age and housing temperature on egg quality at lay and during storage. Methods: Isa Brown hens were used in three experiments. Experiment 1: 55-week-old hens were exposed to acute transport and relocation stress and normal-shelled eggs collected before and after the stress and during storage were assessed. Experiment 2: investigated hen age effects on egg quality: Eggs for hens aged 21, 30, 50 and 63 weeks, housed in the same shed, were assessed for egg quality at lay and during storage. Experiment 3: investigated housing temperature effects on egg quality. Hens aged 47, 56, and 57 weeks were housed during winter and aged 30, 37, and 40 weeks in summer. Egg quality was determined at lay and during storage. Across experiments, eggs were collected on a single day. Egg quality was measured using Haugh Unit (HU) at lay (control) and weekly during 28 days of storage in a refrigerator (4.1-4.3℃), cool room (15.8-16.1℃), or open room (21.2-21.8℃). Eggshell morphology was visually assessed. Key results: Experiment 1: 32.5% of eggs laid exhibited abnormal shell morphologies, while 67.5% were normal-shelled eggs. The normal shell eggs had similar HU values compared to pre-transport control. Experiment 2: Hens aged 50 and 63 weeks showed similar HU measures during storage. Experiment 3: Winter shed temperature had no effect on HU at lay or during refrigeration and room temperature storage. Conclusions: When evaluating egg quality from different production systems, sampling normal-shell eggs from Isa Brown hens aged 50-63 weeks with shed temperature below 25°C would eliminate confounding influences of shed temperature, hen age and stress. Implications: Eliminating these confounding influences would help validate a further study evaluating the effects of different production systems on egg quality.