Effects of multimodal early-life stress on physiological stress responses, behaviour, and caecal microbiota in Pekin and Muscovy ducks subjected to road transportation

This study investigated whether exposure to multimodal early-life stress modifies physiological stress responses, fear behaviour and selected caecal bacterial populations in Pekin and Muscovy ducks subjected to road transportation under tropical conditions. A total of 416 male ducklings (Pekin, n = 208; Muscovy, n = 208) were assigned to early-stress (ES) or no early-stress (NES) treatments from days 3 to 14. Early-stressed ducks were exposed daily for 3 h to a combination of crating, mild cold (24 ± 1°C), noise (100 dB), and darkness. On day 42, ducks were either transported for 3 h or remained in their home pens. We evaluated serum corticosterone (CORT) and heat shock protein 70 (HSP70) levels, tonic immobility (TI) responses, selected caecal bacterial populations, and growth performance. Early-life stress did not affect growth performance, feed efficiency or mortality. Muscovy ducks exhibited longer TI duration and required fewer inductions than Pekin ducks, suggesting that different breeds respond differently to fear, whereas early-life stress and transportation did not affect underlying fearfulness. CORT responses to transportation were strongly breed-dependent. Pekin ducks showed higher corticosterone concentrations than Muscovy ducks, and early-stressed Pekin ducks exhibited lower CORT following transportation compared with non-early-stressed transported ducks. In contrast, early-life stress had little effect on CORT responses in Muscovy ducks. Heat shock protein 70 was not influenced by early-life stress or transportation. Ducks that were not exposed to early-life stress and were subsequently transported showed the lowest caecal Lactobacillus spp. counts. The results suggest that early-life stress across multiple modalities can reduce physiological stress responses triggered by transportation and promote gut microbial stability in Pekin ducks while maintaining their performance. In contrast, Muscovy ducks show minimal additional advantages, underscoring the breed-specific responses to early-life conditioning strategies.