Chronic heat stress in Iranian fat-tailed ram lambs: clinical and paraclinical parameters

The effect of heat stress on physiological parameters has been well documented. However, there are reports of a genetic based heat tolerance in some sheep breeds. The aim of the present study was to monitor the physiological responses of an Iranian fat-tailed breed against heat stress and an acute stress insult. Atotal number of 15 fall-born ram lambs were selected and subjected to direct summer solar radiation throughout the day (May 2009 to February 2010). Ten lambs were semi-castrated in October to see the physiologic response of animals to an acute stress. The general parameter as well as blood chemistry and cortisol were analyzed during the study. The results showed that all physiologic parameters had significant changes; however, their values were in normal range. The fact that the animals in the present study experienced their first exposure of heat stress and a significant increase in serum cortisol concentration in semicastrated lambs in October, compared to the respected values in the hottest months of the experiment, may indicate a genetic based adaptability of the breed in Iran. The present study shows the dynamic changes of general and biochemical parameters in response to chronic heat stress and an acute stress that raises a possible tolerance of the breed against heat stress.