High-carotenoid orange corn diet altered serotonin and dopamine activity in the brain while heat stress altered total antioxidant capacity in a sex dependent manner in Pekin ducks

Carotenoids have antioxidant properties that may enhance heat tolerance and affective state in poultry. This study investigated whether a high-carotenoid orange corn (OC) diet modulates total antioxidant capacity (TAC) and brain neurotransmitters (NT) in adult Pekin ducks exposed to heat stress (HS). Pekin ducks (224 hens, 56 drakes) were fed OC or yellow corn (YC) diets (n = 4 pens/treatment; 28 hens and 7 drakes/pen) for 3 weeks before and during 3 weeks of cyclic HS (35°C for 10 h/day). Blood samples were collected from randomly selected ducks (n = 8/sex/treatment/timepoint) and brain tissues (n = 12 hens, 8 drakes/treatment/timepoint) were collected before and after HS. NT levels (n = 6/sex/treatment/timepoint) were quantified in the diencephalon (DI), lateral telencephalon (LT), mesencephalon (ME), and medial telencephalon (MT). HS significantly decreased (p < 0.001) brain TAC in hens but not in drakes. Serum TAC increased (p < 0.001) in both sexes with HS whereas no diet effect was detected. In the brain, OC hens exhibited lower dopamine (DA) levels (p < 0.05) in the MT and LT compared to YC hens, both before and during HS respectively. HS decreased DA in the DI of OC drakes (p < 0.05) and increased DA in the LT of YC hens (p < 0.05) compared to their respective baselines. DA turnover was lower in the DI of OC drakes (p = 0.055) but higher in the LT of OC hens (p < 0.05) compared to their YC groups during HS. OC drakes also showed increased DA turnover from YC drakes at baseline. Across groups, drakes showed higher DA turnover than hens (p < 0.05). HS decreased serotonin (5-HT) in the DI of OC drakes (p = 0.059), and across groups 5-HT was higher in hens than drakes (p < 0.05). 5-HT turnover in the ME was lower in OC hens compared to YC hens during HS (p < 0.05). These findings showed a sex- and brain-region-specific effects of HS and OC diet on TAC and central NT activity in breeder ducks.