Effects of Maternal Stress on Measures of Anxiety and Fearfulness in Different Strains of Laying Hens

Abstract

Maternal stress can affect the offspring of birds, possibly due to hormone deposition in the egg. Additionally, phenotypic diversity resulting from domestication and selection for productivity has created a variety of poultry lines that may cope with stress differently. In this study, we investigated the effects of maternal stress on the behavior of different strains of laying hens and the role of corticosterone as its mediator. For this, fertilized eggs of five genetic lines-two brown (Brown 1 and 2), two white (White 1 and 2), and one pure line White Leghorn-were reared identically as four flocks of 27 birds (24F: 3M) per strain. Each strain was equally separated into two groups: Maternal Stress ("MS"), where hens were subjected to a series of daily acute psychological stressors for 8 days before egg collection, and "Control," which received routine husbandry. Fertile eggs from both treatments were collected at three different ages forming different offspring groups that were treated as replicates; additional eggs from Control were injected either with corticosterone diluted in a vehicle solution ("CORT") or just "Vehicle." Eggs from each replicate were incubated and hatched, and offspring (N = 1,919) were brooded under identical conditions. To measure the effects of maternal stress on anxiety and fear-like behavior, offspring were subjected to a social isolation test (SI) between 5 and 10 days of age and a tonic immobility test (TI) at 9 weeks of age. Compared to Control, MS decreased the number of distress vocalizations emitted by White 2 in SI. No effects of MS were observed in TI, and no effects of CORT were observed in any tests. Overall, brown lines vocalized more in SI and remained in TI for a longer duration than white strains, suggesting genetic differences in fear behavior. Females vocalized more than males in TI and showed a trend toward significance for the same trait in SI. Overall, results suggest that the effects of maternal stress on fearfulness are not directly mediated by corticosterone. Moreover, it highlights behavioral differences across various strains of laying hens, suggesting that fear responses are highly dependent on genotype.

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

“…The physical restraint procedure is a well validated test (39) that was used twice in this study: as a stressor in the parent stock and as a measure of stress response in the offspring. As previously reported (11), the layers from the MS treatment were still physiologically responsive to the stressor even after repeated exposure, therefore, validating the physical restraint test as a stressor in the MS treatment. However, no further stressors applied onto the breeder flock in the MS treatment were validated, thus limiting the discussion on whether the lack of effects in the progeny of MS breeders is due to a natural resilience of the breeder hens to the chosen stressors, or to an embryonic resilience to increased hormone levels deposited into the egg by the stressed breeder.…”

“…Maternal stress can impact offspring’s physiology, behaviour and cognition (6,8) through structural and functional changes in brain areas involved in the mediation of fear and anxiety (9), as well as through changes in gene expression (10). We have previously shown that chicks from a commercial line of layer breeders that were subjected to daily sessions of psychological stressors during egg production showed a decreased occurrence of anxiety-like behaviour (measured in the total number of distress calls expressed during social isolation) compared to a control group (11). In addition, laying hens subjected to unpredictable feed restriction had chicks that stayed longer in tonic immobility (a measure of fearfulness) and spent less time eating when competing with birds from the control group for access to feed in a novel environment (12).…”

Effect of a Synbiotic Supplement on Fear Response and Memory Assessment of Broiler Chickens Subjected to Heat Stress

“…Shi et al [82] reported that hens kept in colony cages had higher plasma CORT with greater fearfulness and feather damage compared to hens housed in colony cages with nest boxes. In contrast, Peixoto et al [83] reported that the effect of maternal stress on fearfulness in laying hens is not directly mediated by CORT. Similarly, in the current study, plasma CORT concentrations were not affected by the dietary treatment, regardless of its concentrations: 2.37 ng/mL (G-C), 2.19 ng/mL (G-0.5), 2.24 ng/mL (G-1.0).…”

Maternal age and maternal environment affect stress reactivity and measures of social behaviour in laying hens

“…Likewise, Japanese quails subjected to stressful events, such as sudden movement or unpredictable noise, laid eggs with higher yolk testosterone and progesterone, and produced chicks more sensitive to social separation (i.e., vocalized more during emergence and open-eld tests) 13 . Interestingly, stressful events applied onto ve genetic lines of layer breeders decreased offspring's sensitivity to social isolation in only one line, suggesting that maternal effects are also dependent on genetics 14 .…”

“…To our knowledge, no research has yet investigated the combination of maternal age and maternal environment in laying hens. The current study -which is part of a more comprehensive research project on maternal effects 14,26,[29][30][31][32] -investigates how maternal age, maternal rearing experience and maternal adult housing system affect their offspring's behaviour and stress response. For this, we conducted two experiments.…”