EFFECT OF INCREASED RECTAL TEMPERATURE ON NITROGEN METABOLISM IN BRAHMAN CROSS AND SHORTHORN X HEREFORD STEERS FED ON LUCERNE CHAFF

A study was made of the effect on nitrogen metabolism of increasing the rectal temperature of Brahman cross and British steers on controlled feed intake. When the rectal temperature of the British steers was 1.3 degC higher than that of the Brahman cross steers, they excreted 13.5 g urinary nitrogen per day more than the Brahman cross. When the Brahman cross steers had a rectal temperature 1.3 degC higher than the British, they excreted 8.7 g urinary nitrogen per day more than the British steers. At the same nitrogen intake there was no significant breed difference in the increase in urinary nitrogen per degree rise in rectal temperature. Increasing the rectal temperature had a small effect on appetite but did not affect the apparent nitrogen digestibility; the concentration of nitrogen in the faecal dry matter was higher under the heat treatment. The ambient temperature at which rectal temperatures were increased by 1.3 degC was about 31°C for the British steers and 45° for the Brahman cross steers. At the increased rectal temperature the Brahman cross steers drank significantly more water than the British steers although faecal and urinary water losses were similar. © 1969 CSIRO. All rights reserved.