Rectal temperature as an indicator for heat tolerance in chickens.

Abstract

High environmental temperature is perhaps the most important inhibiting factor to poultry production in hot regions. The objective of this study was to test adaptive responses of chickens to high ambient temperatures and identify suitable indicators for selection of heat-tolerant individuals. Full-sib or half-sib Anak-40 pullets (n&#x2009;=&#x2009;55) with similar body weights were raised in a room with a temperature ranging from 24&#xb0;C to 28&#xb0;C, and relative humidity of 50% from 61 to 65 days of age. On day 66, the ambient temperature was increased within 60&#x2009;min to 35&#x2009;&#xb1;&#x2009;1&#xb0;C which was defined as the initial of heat stress (0&#x2009;h). Rectal temperature (RT) was measured on each pullet at 0, 6, 18, 30, 42, 54 and 66&#x2009;h. After 66&#x2009;h the ambient temperature was increased within 30&#x2009;min to 41&#x2009;&#xb1;&#x2009;1&#xb0;C and survival time (HSST) as well as lethal rectal temperatures (LRT) were recorded for each individual. The gap between the RT and initial RT was calculated as &#x394;Tn (&#x394;T6, &#x394;T18, &#x394;T30, &#x394;T42, &#x394;T54 and &#x394;T66), and the interval between LRT and initial RT as &#x394;TT, respectively. A negative correlation was found between HSST and &#x394;Tn as well as &#x394;TT (r&#x394; T 18 &#x2009;=&#x2009;-0.28 and r&#x394; TT &#x2009;=&#x2009;-0.31, respectively, P&#x2009;<&#x2009;0.05; r&#x394;T30 &#x2009;=&#x2009;-0.36, r&#x394; T 42 &#x2009;=&#x2009;-0.38, r&#x394;T54 &#x2009;=&#x2009;-0.56, P&#x2009;<&#x2009;0.01). Importantly, pullets with low &#x394;T18 showed a longer HSST (256.0&#x2009;&#xb1;&#x2009;208.4&#x2009;min) than those with high &#x394;T18 (HSST&#x2009;=&#x2009;123.7&#x2009;&#xb1;&#x2009;78.3&#x2009;min). This observation suggested that the &#x394;T18 or early increment of RT under heat stress might be considered as a reliable indicator for evaluation of heat resistance in chickens.