Abstract
This study was conducted to compare the effects of thermal stress on growth performance and some immunity variables of broiler chickens. Birds were randomly assigned to one of three thermal treatments as follows: cold stress (CS, 12±1°C), (b) heat stress (HS, 33±3 °C) and (c) thermoneutral (TN, 24±2 °C). Body weight gain (BWG), feed intake (FI), water intake (WI) and feed conversion ratio (FCR) were recorded. In order to evaluate the primary and secondary humoral immune responses, two birds per replicate were intravenously administrated with a suspension of 7% sheep red blood cell (SRBC) at 28 and 35 days. The heat-stressed broiler chickens had lower FI (-14.90%), BWG (-25.71%) and higher FCR (+13.06%) in comparison to broiler chickens reared under TN condition (p<0.001) from 1 to 42 days of age. The cold-stressed broiler chickens showed lower FI (-22.05%), BWG (-38.32%) and higher FCR (+22.47%) in comparison to birds reared under TN conditions (p<0.001). Stressed birds (CS and HS) showed decreased antibody titer against SRBC, lymphocyte count and the relative weights of lymphoid organs and increased heterophil count, heterophil to lymphocyte ratio and the serum concentration of corticosterone, in comparison to birds in TN group (p<0.001). In conclusion, HS and CS conditions have similar negative effects on performance and immunity of broiler chickens.
Highlights
Birds are usually faced with environmental stresses while bred
The birds in the HS group showed a lower feed intake (FI) (-25.15%), BW (-40.25%), and higher feed conversion ratio (FCR) (+21.29%) and water intake (WI) (+13.35%) in comparison to the birds reared under TN condition (p
Considering the whole rearing period (1 to 42 days of age), broiler chickens submitted to HS exhibited lower FI (-18.30%), BW (-26.92%), higher FCR (+11.05%) and WI (+11.17%) in comparison to the birds reared under TN condition (p
Summary
Stress is defined as a biological reaction of animals to environmental stimuli, being considered a major challenge in the poultry industry, because of its unfavorable effects on growth performance. Both intrinsic and extrinsic negative stressors change body homeostasis in animals. The Royal Society for the Prevention of Cruelty to Animals (RSPCA), in its welfare standards for meat chicken, has recommended monitoring animals for having access to a thermal comfortable environment at all times, preventing both heat (HS) and cold stress (CS). The World Organization for Animal Health (OIE) standards recommends avoiding severe heat, humidity and cold (Stevenson et al, 2014). In order to prevent these environmental stresses, the OIE has advised to employ higher air speed, evaporative cooling and reducing stocking density (Stevenson et al, 2014)
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