Selecting Merino rams for ability to withstand infertility caused by heat. 2. The effect of heat on scrotal and testicular blood flow

Abstract

Rams selected for and against skin wrinkle (Folds Plus and Folds Minus) are known to differ in their susceptibility to infertility caused by heat. Rams of these types were therefore subjected to heat and the differences in their reactions studied in an attempt to cast light on the mechanisms involved in scrotal heat tolerance. An experiment to investigate the relationship between the degree of heat load to the scrotum and testes to ram fertility suggested that the scrotum and perhaps also the testes play an active role in modifying the damaging effects of high temperature. One of the factors that could influence the amount of heat reaching the testes is scrotal blood flow and this was found to increase with increases in scrotal temperature. Folds Minus rams showed greater increases than Folds Plus rams but only after 2.5 hours at a scrotal temperature of 40¦C. In all rams the lower regions of the scrotum showed a greater increase in blood flow than upper regions. Folds Plus rams showed no increase in testicular blood flow as temperature increased but Folds Minus rams showed an increased testicular blood flow at 40¦C.