Wool cortisol is a better indicator of stress than blood cortisol in ewes exposed to heat stress and water restriction.

This study investigated the effect of water restriction on wool and blood cortisol concentrations and water consumption patterns in heat-stressed sheep. Nine Corriedale female sheep (average BW=43±6.5 kg) were individually fed diets based on maintenance requirement in metabolic crates. They were assigned to three treatments according to a Latin square design (3×3) for three periods with a 21-day duration for each period (nine sheep per treatment). Treatments included free access to water (FAW), 2 h water restriction (2hWR) and 3 h water restriction (3hWR) after feeding. Average temperature-humidity index in the experimental room was 27.9 throughout the experiment that defines heat stress conditions. Wool samples were taken at the end of each period on day 21. No differences were found in cortisol concentration in each fragment (dried, washed and residual extract) of wool (P<0.05). Total wool cortisol concentration was higher in the 3hWR group than the other treatments (P<0.05). Blood cortisol was not different among the treatments (P>0.05) and resulted in higher variable data compared with wool cortisol. Blood neutrophils and neutrophil/lymphocyte ratio suppressed in FAW and 3hWR groups compared with the 2hWR group (P<0.05). The duration of water consumption recorded after feeding in the 3hWR group was higher than in the 2hWR group when recorded in the afternoon (P<0.01). Water consumption rate was higher in the 3hWR group than in the 2hWR group (P<0.01). However, total water consumed was lower in the 3hWR group compared with other treatments (P>0.05). It can be concluded that wool cortisol provides more precise and accurate data than blood cortisol during heat stress conditions. Water restriction for 3 h after feeding can act as a stressor and is critical for sheep during heat stress as the consumption of water decreases with restriction.