Stress-induced oviposition delays in laying hens: duration and consequences for eggshell quality.

1. This study investigated relationships between the timing of stress, duration of oviposition delays and consequences for eggshell quality, in 2 experiments with ISA Brown hens. 2. Periods of up to 6 h of environmental stress (relocation from an individual cage to a larger one containing 3 unfamiliar hens), commencing up to 4.5 h before predicted oviposition time, reliably induced oviposition delays. Many hens still retained their egg when stress ended. 3. Ovipositions that occurred during stress were never delayed for more than 3.0 h beyond the expected time. Ovipositions that occurred after the period of stress ended usually did so after <1 h if the delay at the end of stress was less than about 2.4 h. Delays that ended either during stress or <2 h after stress ended were classified as short-term. 4. If an oviposition delay was more than about 2.4 h when stress ended, the egg concerned was usually laid much later, after a delay of 7 to 15 h. Delays that ended >5 h after stress ended were classified as long-term. 5. Eggs delayed long-term were white-banded and the subsequent egg was slab-sided, or occasionally soft-shelled. Short-term delays often caused eggshell dusting with varying amounts of superficial calcification. Hence, duration of oviposition delay affects both the number of abnormal eggshells and the degree of abnormality. 6. The present findings are of potential importance to both the egg industry and breeders, because abnormal eggshells cause downgrading and can impair embryonic development. Also, numbers of abnormal eggshells and degree of abnormality can be used as indicators of environmental stress.