Effect of heat stress on in-vitro sperm parameters in rams

Effect of environmental or artificially induced heat stress on reproduction have been studied in different species such as human, mouse, rabbit, bull and ram. However, the number of studies related to the effect of heat stress on ram spermatozoa was not adequate. Also most of these studies have evaluated the effect of heat stress on basic sperm parameters in rams. This study was designed to evaluate the effects of environmental heat stress on ram spermatozoa in a wider perspective. Semen (n=72) was collected from six mature rams monthly by electro-ejaculator throughout a year. Ejaculates (n=36), which were collected between May and October, were regarded as heat stressed samples and the ejaculates (n=36), which were collected in the remaining six months from November to April, were regarded as the control samples. This way of classification also provided an equal distribution of the breeding season between heat stress and control periods. Sperm samples which represent control and heat stress periods were compared for different sperm parameters such as semen volume, concentration, motility, live-dead sperm rate, abnormal sperm rate, plasma membrane and DNA integrity and percentage of acrosome reacted sperms. Heat stress decreased concentration, motility and plasma membrane integrity of sperm cells (P<0.05) along with an increase in the percentage of dead and abnormal sperm rates in rams (P<0.05). In conclusion, environmental heat stress can affect detrimentally some sperm parameters such as concentration, motility, plasma membrane integrity of spermatozoa, along with the percentage of morphologically normal and live sperm rate in rams.