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: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. 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 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. 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.