The effect of ruminal escape protein and ambient temperature on the efficiency of utilization of metabolizable energy by lambs1

Abstract

Forty-eight crossbred lambs (22.5 +/- 2.6 kg average BW) of equal numbers from both sexes were used to observe the effect of protein supplement (none, canola meal, or fish meal) and temperature (21 +/- 1.8 degrees C or 4.7 +/- 1.7 degrees C) on growth and energetic efficiency in a 2 x 3 x 2 factorial experiment. Twelve lambs were slaughtered at the onset of the trial to determine initial body composition. The remaining 36 were fed diets consisting of 50% concentrate and 50% straw at DMI of 77 and 83 g/kg.75 daily in the warm and cold, respectively, for an 85-d period. Daily gains of the control lambs and of those supplemented with canola and fish meal were 80, 94, and 101 g/d, respectively; however, no differences in efficiency of live weight gain could be detected. Apparent digestibilities of DM, GE, OM, and fiber were decreased (P < .05) in response to the cold. Methane production was increased (P < .01) in the cold. Metabolizable energy intake was not increased by exposure to cold, even though DMI was higher (P < .1) in the cold. Cold-treated lambs retained less (P < .01) total energy as well as less (P = .02) fat energy as determined by comparative slaughter. Supplementation with protein increased (P < .05) energy retained as protein; however, it did not affect total energy retained or energetic efficiency. Energy retention estimated from the calorimetry-balance technique was 30 to 80% greater than that estimated from the comparative slaughter technique. It was concluded that methane production in lambs with short fleece was increased when the temperature was reduced from 21 to 5 degrees C and that energetic efficiency was not affected by the concentration or type of protein in the diet.