Chronic heat stress part 1: Decrease in egg quality, increase in cortisol levels in egg albumen, and reduction in fertility of breeder pekin ducks

Abstract

Global warming poses detrimental effects on poultry production leading to substantial economic losses. The goal of our experiment was to test the hypothesis that heat stress (HS) would alter welfare and egg quality (EQ) of breeder ducks. Furthermore, we wanted to test if HS would increase cortisol levels in egg albumen. Adult Pekin ducks were randomly assigned to two different rooms at 85% lay with 60 hens and 20 drakes per room. Baseline data including body weight, body condition scores (BCS), and egg production/quality were collected the week preceding heat treatment. Ducks were subjected to cyclic HS of 35°C for 10h/day and 29.5°C for the remaining 14h/day for 3 weeks while the control room was maintained at 22°C. Eggs were collected daily and analyzed weekly for quality assessment, and for albumen glucocorticoid (GCs) levels using mass spectrometry. One week before the exposure to HS, 10 hens and 5 drakes were euthanized and the same number again after 3 weeks and birds necropsied. Data analyses were done by 1- or 2-way ANOVA as appropriate with a Tukey-Kramer post hoc test. BCS were analyzed using a chi-squared test. A p ≤ 0.05 was considered significant. Circulating levels of corticosterone were significantly (p < 0.01) elevated at week 1 only in the HS hens. The circulating levels of cortisol increased significantly at week 1 and 2 (p < 0.05), and week 3 (p < 0.01) in the hens and at weeks 2 and 3 only (p < 0.05) in the drakes. Feather quality scores (p < 0.01), feather cleanliness scores (p < 0.001) and footpad quality scores (p < 0.05) increased significantly in the HS group. HS elicited a significant (p < 0.001) decrease in egg production at weeks 1 and 3. Hens in the HS group showed significantly decreased BW (p < 0.001) and number of follicles (p < 0.05). Shell weight decreased significantly at week 1 only (p < 0.05) compared to controls. Yolk weight decreased significantly at week 3 (p < 0.01) compared to controls. HS elicited a significant increase in albumen cortisol levels at week 1 (p < 0.05) and week 3 (p < 0.05). Thus, cortisol may provide critical information to further understand and to improve welfare.

Catecholamine concentrations in duck eggs are impacted by hen exposure to heat stress

“…While glucocorticoids are detectable in egg contents ( Caulfield and Padula, 2020 ; Oluwagbenga et al, 2022 ), limited attention has been directed towards how stressors encountered in modern poultry production, such as heat stress, may affect catecholamine and catecholamine precursors in albumen and yolk. Previously it was reported that catecholamines are detectable in chicken egg yolk and are elevated in response to stress ( Moudgal et al, 1990a ; Moudgal et al, 1990 ).…”

“…Glucocorticoids, androgens, and nutrients can be transferred from mother to egg via the yolk and albumen and can have significant effects on the phenotype of the developing offspring ( Eising and Groothuis, 2003 ; Hayward and Wingfield, 2004 ; Caulfield and Padula, 2020 ). In the same eggs analyzed in this study, we separately assessed glucocorticoid levels and found increased cortisol in the albumen ( Oluwagbenga et al, 2022 ). The combination of both catecholamine and glucocorticoid may lead to specific patterns of DNA methylation during embryogenesis, although this has yet to be determined and requires further studies.…”

“…Nest boxes were placed along one wall of the room with four hens per nest box as per industry standards ( Chen et al, 2021 ), and all eggs collected daily. Details of the study design were published elsewhere ( Oluwagbenga et al, 2022 ). Briefly, heat stress or control conditions began when the hens reached 85% lay.…”

“…Eggs from control and heat stress groups ( n = 12 eggs/group/timepoint) were collected on the same day prior to the onset of HS (baseline), and then at the end of each week over the 3 weeks heat stress period. Details of the egg collection procedure were previously published ( Oluwagbenga et al, 2022 ). Due to the number of hens compared to number of nest boxes typical for industry and research, we are not capable at this time to associate an egg with the hen whom laid that specific egg.…”

Chronic treatment with glucocorticoids does not affect egg quality but increases cortisol deposition into egg albumen and elicits changes to the heterophil to lymphocyte ratio in a sex-dependent manner

“…Prolonged periods of increased circulating levels of GC compromise the immunity, welfare, health, performance, and overall productivity of the bird resulting in economic losses and a decline in product quality (Post et al, 2003;Quinteiro-Filho et al, 2012;Zeng et al, 2014;Honda et al, 2015). The potential for elevated circulating levels of GC to mediate detrimental effects on production and performance parameters can be achieved through the direct introduction of the GC to the birds via implantation (Hayward and Wingfield, 2004), injection, oral administration in feed or water (Shini and Kaiser, 2009;Kim et al, 2015), or through the direct introduction of stimuli such as heat (Videla et al, 2020;Oluwagbenga et al, 2022), transportation (Vosmerova et al, 2010;Tetel et al, 2022b), or feed restriction (Najafi et al, 2015) to alter the HPA axis and stimulate the release of GC.…”