Impacts of Enrichment Type (Hut vs. Platform) on Chronic Stress and Anxiety in Six Fast- and Slow-Growing Broiler Strains.

The objective of this study is to assess anxiety and chronic stress in fast- and slow-growing broilers when housed with a hut or platform enrichment. We obtained 264 day-old chicks each of Cobb 500, Ross 308, and Ross 708, Redbro-Yield, Redbro M, and Ja57NH strains, and placed them by strain across 72 pens (22 birds/pen) with an A-frame hut or a perforated platform with ramps. Anxiety was assessed via the attention bias test (proportion of birds feeding, vigilance), and chronic stress was assessed through feather corticosterone (fCORT) and secretory immunoglobulin-A (SIgA) concentrations in excreta at 3.7 kg body weight. More Ja57NH broilers began feeding during the test compared to Cobb 500 (p = 0.037) and Ross 708 (p = 0.033) broilers. Redbro M broilers were less vigilant than Ross 308 broilers (p = 0.038). Redbro M broilers had lower fCORT concentrations than Ja57NH broilers (p = 0.019). Redbro M and Ja57NH broilers had lower SIgA concentrations than all fast-growing strains. Enrichment type had no impact on anxiety or chronic stress responses. Both Ja57NH and Redbro M broilers showed improved indicators of affective state (less vigilance, tended to feed more during the test, lower fCORT concentrations) compared to other strains assessed at market weight. SIgA levels seemed strongly impacted by genetics, so SIgA may not be appropriate as an inter-strain comparison of chronic stress. The two fastest-growing broiler strains were genetically predisposed to greater anxiety compared to the two slowest-growing strains, which has implications for their welfare.