The effect of increased rectal temperature on nitrogen metabolism in Brahman cross and Shorthorn × Hereford steers fed on a low nitrogen roughage

Abstract

A study was made of the effect of increasing the rectal temperature on nitrogen metabolism in Brahman cross and British cross steers offered a fixed amount of a low nitrogen roughage. Increasing the rectal temperature by c. 1.3¦C in either breed slightly depressed intake, increased the dry matter digestibility by a small but statistically significant amount, and had no effect on the nitrogen digestibility. It did not significantly increase the urinary excretion of total nitrogen or urea nitrogen over the whole collection period, but over the last 5 days there were increases in the urinary total and urea nitrogen excreted per day which in most cases were significant. Increasing the rectal temperature significantly increased the urinary excretion of creatinine. The ambient temperature at which rectal temperatures were increased by 1.3¦C was 35¦C for the British cross steers and 43' for the Brahman cross steers. At the increased rectal temperature, the Brahman cross steers drank significantly more water than the British cross steers although faecal and urinary water losses were not significantly different. The calculated evaporative water loss was higher in the Brahman cross steers than in the British cross steers when both breeds were heated.