Research Note: Effects of high barn temperature on group-level dispersion and individual activity in broiler chickens

Abstract

Heat stress in broilers is a pressing issue in the changing climate. Data on broiler behaviour might be useful for early detection of heat stress and subsequent intervention, and may provide potential indicators for heat tolerance that can be used in broiler breeding programs. Here, we used bird location data collected in a previous study during which broilers were inadvertently exposed to high ambient temperatures due to a local heat wave. We examined whether broiler behaviour changed with increasing ambient temperatures, focusing on group-level dispersion behaviour and individual-level locomotor activity. We observed that birds moved closer together with increasing temperatures up to 9 degrees Celsius above the desired level, and remained in similar proximity or moved further apart at temperatures above that threshold. The activity level decreased or remained stable with increasing temperature during most parts of the day, but increased at the end of the day. Possibly, the birds exhibited compensatory behaviour (such as drinking and eating) during the periods when the barn cooled down after a hot day, but that could not be confirmed as no behavioural observations were available. The difference in activity levels between individuals accounted for 8.4% of the total variation, suggesting that activity might be an interesting indicator trait for heat tolerance in broiler chickens. Overall, the results of this study can inform the development of behaviour-based 1) early-warning systems for heat stress and 2) heat tolerance indicators, although data on behaviours that are more specific to heat stress are probably required.