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

Abstract

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