Sex differences in glucocorticoid responses to shipping stress in Pekin ducks

Abstract

Some concerns have been raised recently about the assay of corticosterone vs. cortisol in poultry species. Thus, we tested the hypothesis that ducks secrete both glucocorticoids. First, we validated two commercially ELISA kits for the two glucocorticoids by first charcoal stripping duck serum in order to remove all steroid hormones. We ran serial dilutions of spiked, charcoal-stripped serum on kits of opposite glucocorticoid as well as a serial dilution using the respective ELISA buffer of the opposite assay kit. We found that the glucocorticoid standard curve in duck serum matched the respective curve in that kit's own buffer. However, when the opposite hormone was run in each kit in both duck serum or ELISA buffer, a near zero slope was obtained. Second, we further validated the presence of both glucocorticoids using mass spectrometry. Third, we tested the hypothesis that exogenous ACTH would stimulate the release of both corticosterone and cortisol. And, fourth, we tested the hypothesis that each glucocorticoid would have different serum levels in response to shipping stress. To test this hypothesis, we collected serum from 10 drakes and 10 hens from 2 flocks (N = 20 per time point per sex): 24 h prior to shipping, at shipping as ducks were walked off the truck, 24 h after shipping, and 1 wk after shipping. Data were analyzed by 2-way repeated measures ANOVA. Surprisingly, we also observed a sex difference in both glucocorticoid levels in that hens showed higher ( P < 0.01) serum levels than did drakes at all-time points in response to either ACTH or transportation. Finally, no differences were observed in either glucocorticoid levels associated with shipping in either sex. The fact that both glucocorticoids are released in measurable amounts lends to the possibility that they may be differentially regulated, or at least there is a sex difference in the neural pathways associated with glucocorticoid release in ducks. Although corticosterone is the likely predominate glucocorticoid in ducks, serious attention should be given to the role of cortisol in poultry. Further consideration of sex, age, and timing of blood collection to stressor needs to be considered when assessing glucocorticoid levels in any avian species.

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

“…Blood samples were collected from the ducks' tibial veins at the same time as blood smears on weeks 0, 1, 2, and 3 relative to the onset of HS from randomly selected ducks at each time point (n = 6/sex/treatment/week) and placed into a serum separator tubes, centrifuged, and the serum was stored at −20 °C until assayed by ELISA for GC (Tetel et al, 2022a;Tetel et al, 2022b). Daily eggs laid (n = 35-60) were counted and 3 consecutive day eggs (thus n = 3 per time group) were averaged to reduce daily lay variability and compared between treatment groups beginning 1 week prior to HS treatment (n = 3/group/treatment): groups -1 and 0 (week preceding heat stress), groups 1 and 2 (week 1), groups 3 and 4 (week 2), and groups 5, 6 and 7 (week 3).…”

“…The kits utilized for this project were from Cayman Chemicals (corticosterone: kit #16063; cortisol kit #560360) and the assays were run according to the manufacturer's recommendations. Details of the kit verification have been reported previously (Tetel et al, 2022a;Tetel et al, 2022b). Plates were incubated with samples overnight at 4 °C.…”

Research Note: Sex difference in changes in heterophil to lymphocyte ratios in response to acute exposure of both corticosterone and cortisol in the Pekin duck

“…Other studies have similarly shown that females tend to have higher levels of glucocorticoids than do males, particularly in mammals. Our previous studies also showed a significant sex difference in the secretion pattern of both glucocorticoids ( Tetel et al, 2022a , b ). The general or poor lack of effect of the low dose cortisol may suggest that corticosterone is the primary glucocorticoid to effect HLR, however, more investigations are required to confirm that notion.…”

“…Previous results from our lab have shown a sex difference in both corticosterone and cortisol release following shipping stress and in response to treatment with an artificial adrenocorticotropin releasing hormone ( ACTH ; cosyntropin; Tetel et al, 2022a , b ). Glucocorticoids increase HLR by stimulating lymph nodes to release heterophils which elicits an apparent increase in circulating numbers while simultaneously increasing marginalization of lymphocytes which leads to an apparent decrease in numbers.…”

“…Safflower oil was used as the control. The doses were chosen as those shown to elicit responses previously in ducks ( Fowles et al, 1993 ) and that we have shown that circulating endogenous cortisol is typically 25% levels compared to corticosterone in ducks ( Tetel et al, 2022a , b ). Steroids were dissolved in safflower oil for injections.…”