Acute stressors experienced by layer breeders do not affect measures of 4 stress and fear in their offspring 5 6 Mariana R.Abstract 18 Stressors experienced by layer breeders during egg production can lead to changes in the 19 egg hormone content, potentially impacting their offspring, the commercial layers. Genetic 20 differences might also affect the offspring's susceptibility to maternal experiences. In this study, 21 we tested if maternal stress affects measures of stress and fear in five strains of layer breeders:22 commercial brown 1 & 2, commercial white 1 & 2 and a pure line White Leghorn. Each strain was 23 equally separated into two groups: "Maternal Stress" (MS), where hens were subjected to a series 24 of 8 consecutive days of acute psychological stressors, and "Control," which received routine 25 husbandry. Additional eggs from Control were injected either with corticosterone diluted in a 26 vehicle solution ("CORT") or just "Vehicle." Stress-and fear-responses of the offspring were 27 measured in a plasma corticosterone test and a combined human approach and novel object test.28 Both MS and CORT treatments failed to affect the measured endpoints in the offspring, but 29 significant strain differences were found. The offspring of the white strains showed a higher 30 physiological response compared to brown strains, but the White 2 offspring was consistently the 31 least fearful strain in the behaviour tests. Our study found that the acute psychological stressors 32 experienced by layer breeders did not affect the parameters tested in their offspring and that 33 corticosterone does not seem to be the primary mediator of maternal stress in laying hens. This is 34 highly important, as in poultry production, layer breeders are often subjected to short-term 35 stressors. In addition, we successfully dissociated the physiological and behavioural parameters of 36 stress response in laying hens, showing that increased concentrations of plasma corticosterone in 37 response to stress is not directly associated with high levels of fear.3 38 53 54Once believed that only genetic selection could shape the phenotype of the progeny, it is 55 now known that the over-activation of the hypothalamic-pituitary-adrenal (HPA) axis (i.e., stress 56 response) experienced by the female during egg production can have long-lasting effects in the 57 offspring (3). It has been suggested that these "maternal effects" may shape the phenotype of 58 offspring, which could be adaptive if mother and offspring share similar environments; or 59 detrimental if their environments differ ("environmental matching hypothesis" (3)). Likewise, 60 given that the global population of commercial layers is 7.6 billion birds (4), stressors experienced 4 61 by layer breeders during egg production may directly affect the growth and survival, and possibly, 62 the overall welfare, of billions of commercial laying hens. 63The effects of maternal stress in the offspring of birds and mammals are highly dependent 64 on the intensity, timing of exposure an...