Skin folds and Merino breeding. 6. The effects of varying heat exposures and degree of skin fold on rectal, scrotal, and testis temperatures

Abstract

During exposures of up to 12i hours duration at air temperatures of 30¦C, 35¦C, 40¦C, and 45¦C, Folds Minus rams maintained lower subcutaneous scrotal and intra-testicular temperatures than Folds Plus rams. This was observed with rams from two separately established skin fold selection experiments (Trangie and Cunnamulla). It therefore seems unlikely that the association between skin fold and the ability of rams to withstand heat is due to chance genetic sampling variation that might occur in small closed flocks of sheep. Cunnamulla Folds Plus and Folds Minus rams had similar rectal temperatures. Trangie Folds Plus rams had higher rectal temperatures than, those of Trangie Folds Minus rams but only at air temperatures of 30¦C and 35¦C. The differences in testicular temperature between the two types of rams are probably more dependant on differences in scrotal thermoregulatory function than on differences in body temperature. It has also been shown that the difference in scrotal thermoregulatory function for rams from the Trangie skin fold selection flocks is genetic in origin.