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

Background: 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. objectives: 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. methods: a total 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. results: 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 semi-castrated 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. conclusions: 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.