Acute stressors experienced by layer breeders do not affect measures of stress and fear in their offspring

Abstract

Stressors experienced by layer breeders during egg production can lead to changes in the egg hormone content, potentially impacting their offspring, the commercial layers. Genetic differences might also affect the offsprings susceptibility to maternal experiences. In this study, we tested if maternal stress affects measures of stress and fear in five strains of layer breeders: commercial brown 1 & 2, commercial white 1 & 2 and a pure line White Leghorn. Each strain was equally separated into two groups: "Maternal Stress" (MS), where hens were subjected to a series of 8 consecutive days of acute psychological stressors, and "Control," which received routine husbandry. Additional eggs from Control were injected either with corticosterone diluted in a vehicle solution ("CORT") or just "Vehicle." Stress- and fear-responses of the offspring were measured in a plasma corticosterone test and a combined human approach and novel object test. Both MS and CORT treatments failed to affect the measured endpoints in the offspring, but significant strain differences were found. The offspring of the white strains showed a higher physiological response compared to brown strains, but the White 2 offspring was consistently the least fearful strain in the behaviour tests. Our study found that the acute psychological stressors experienced by layer breeders did not affect the parameters tested in their offspring and that corticosterone does not seem to be the primary mediator of maternal stress in laying hens. This is highly important, as in poultry production, layer breeders are often subjected to short-term stressors. In addition, we successfully dissociated the physiological and behavioural parameters of stress response in laying hens, showing that increased concentrations of plasma corticosterone in response to stress is not directly associated with high levels of fear.