Effects of High Temperature on Sperm Morphology and Subsequent Fertility in Merino Sheep

An experiment was made to test the fertility of ram semen showing morphological abnormality due to exposure of the rams to high ambient temperature. Pyriform cells distinguishable by posterior constriction of the head, tailless sperm and an acrosomal cap abnormality were identified. Three groups of 20 Merino ewes were each mated to two rams which had been heated for four days, or for two days, or unheated (control). Heat treatment was given for 8 h daily in a climate chamber at 40.5”C and 45% relative humidity. The percentage of abnormal spermatozoa increased and the fertility decreased with increasing duration of heat treatment. In the ewes mated to four-day heated, two-day heated and control rams respectively, 0, 15 and 60% of ewes lambed.