Skin folds and Merino breeding. 7. The relations of heat applied to the testis and scrotal thermo-regulation to fertility in the Merino ram

Variation in the fertility of Merino rams whose scrota and testes were heated in a chamber enclosing the scrotum was found to be mainly due to variation in the amount of heat reaching the testes. Variation in fertility due to variation in the response of the testes of different rams to the same amount of heat was found to be relatively unimportant. These conclusions are supported by two pieces of evidence. The first is that rams with genetically differing abilities to control the amount of heat reaching their testes have differing fertility when allowed to express this advantage, but similar fertility when they experience similar heat loads to their testes. The second is that a high correlation (r = -0.926 P<0.005) was found between an expression of the amount of heat reaching the testes and the fertility of rams. Various other expressions of the amount of heat reaching the testes were less highly correlated with fertility.