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

BACKGROUND: The effect of heat stress on physiologicalparameters has been well documented. However, there arereports of a genetic based heat tolerance in some sheep breeds.OBJECTIVES: The aim of the present study was to monitor thephysiological responses of an Iranian fat-tailed breed againstheat stress and an acute stress insult. METHODS:Atotal numberof 15 fall-born ram lambs were selected and subjected to directsummer solar radiation throughout the day (May 2009 toFebruary 2010). Ten lambs were semi-castrated in October to seethe physiologic response of animals to an acute stress. Thegeneral parameter as well as blood chemistry and cortisol wereanalyzed during the study. RESULTS: The results showed that allphysiologic parameters had significant changes; however, theirvalues were in normal range. The fact that the animals in thepresent study experienced their first exposure of heat stress anda significant increase in serum cortisol concentration in semicastratedlambs in October, compared to the respected values inthe hottest months of the experiment, may indicate a geneticbased adaptability of the breed in Iran. CONCLUSIONS: Thepresent study shows the dynamic changes of general andbiochemical parameters in response to chronic heat stress and anacute stress that raises a possible tolerance of the breed againstheat stress.