Epigenetic impacts of heat stress on fear and the physiological stress response

Why this research is being done

The purpose of our study was to evaluate the effects of maternal exposure to heat stress (HS) on post-hatch performance, response to an ACTH challenge, welfare, and behavior of the offspring. To achieve these goals, we treated 160 adult drakes and hens at 85% lay to heat stress or control conditions for 3 weeks and incubated the eggs from the last 3 days of the experiment. A key finding of that study was a significant increase in egg albumen cortisol, not corticosterone, from heat stressed birds compared to controls. For our current study, we evaluated the F1 generation in terms of their growth, welfare, fearfulness, and their GC response to an ACTH challenge. Our results suggest that maternal exposure to heat stress causes lower hatch body weight, and elicits greater HPA and fear responses to ACTH and Novel Object Test (NOT), respectively. We further evaluated the production, fear, and ACTH response on the progeny of the heat stressed and control breeders.

Results

Circulating levels of corticosterone were significantly elevated at week 1 only in the HS hens. The circulating levels of cortisol increased significantly at week 1, 2, and 3  in the hens and at weeks 2 and 3 only in the drakes. Feather quality scores, feather cleanliness scores and footpad quality scores increased significantly in the HS group. HS elicited a significant decrease in egg production at weeks 1 and 3. Hens in the HS group showed significantly decreased BW and number of follicles. Shell weight decreased significantly at week 1 only compared to controls. Yolk weight decreased significantly at week 3 compared to controls. HS elicited a significant increase in albumen cortisol levels at week 1 and week 3. Thus, cortisol may provide critical information to further understand and to improve welfare.

We observed that HS-F1 had a lower hatch weight compared to CON-F1, however, growth rates during the 5-week grow-out period were not significantly different between the two flocks. NOT analyses showed that the HS-F1 had a greater fear response compared to CON-F1. Similarly, an ACTH stimulation test showed that the HS-F1 ducks had significantly heightened corticosterone and HLR responses compared to CON-F1 ducks. The HS-F1 showed altered baseline and ACTH-stimulated levels of cortisol compared to controls. Our data suggest that parental exposure to heat stress impacts the phenotype of the F1 generation in Pekin ducks.

Conclusions
  1. Heat stress significantly and negatively impacts the production, health and welfare of breeder Pekin ducks.
  2. These effects are related to an increase in deposition of stress hormones into the eggs.
  3. Offspring of heat stressed ducks are more fearful and have an exaggerated stress response compared to ducks hatched form control parents.
Next Directions
  1. To determine causal relationship between increased egg stress hormone concentrations and altered phenotype of offspring.
  2. To determine the DNA methylation associated with heat stress in breeder ducks.
  3. To determine if DNA methylation events are transferred to progeny and grand-progeny of heat stressed ducks.
Contact information

Gregory S Fraley gfraley@purdue.edu | Purdue ANSC Directory