Summary. The semen collected from twelve Merino rams was ex¬ amined before and after they were exposed during 3 days to two 6-hr periods in a climate room at 40-5°C , After recovery from the first experiment, the same rams were divided into three groups of four. Two groups were exposed to the same heat treatments as before and the third group stood in the climate room for 12 hr at 21°C and 6-8 mm Hg vapour pressure. Water at 17 to 19°C was circulated around the scrotum of one group of rams exposed to heat and of the group in the thermo-neutral environment. Only the rams exposed to heat without their scrota cooled in this way produced semen of inferior quality. It was concluded that under the conditions of these experiments, the efficiency of the heat-dissipating properties of the scrotum alone decided the magnitude of the adverse effects of short periods of raised air temperature on the quality of the semen produced by Merino rams.
The pulsatile blood flow in the internal spermatic artery of the ram is changed by the arterial coils in the spermatic cord so that the testis receives a relatively pulseless blood flow at a lower mean pressure. The major pulse-pressure reduction occurs in the proximal one-third of the coiled length of the artery; in the distal two-thirds, the character of the coiling and structure of the artery change. These observations are discussed particularly in relation to the thermo-regulatory function pre¬ viously suggested for the internal spermatic artery.
A technique for determining intratesticular temperatures of Merino rams is described. Some results of observations on intratesticular temperatures of rams are given. These show increases associated with exposure to high atmospheric temperatures, to rises in rectal temperature, and to wrapping of the scrotum.
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