Effect of food intake on protein and energy metabolism in finishing beef steers

Gerald Lobley, A Connell, Vivien Buchan

Research output: Contribution to journalArticle

36 Citations (Scopus)

Abstract

The effects of progressive reduction in food intake from 1.6 X maintenance (1.6 M) to approximately maintenance (M') and then to zero (fasting) on energy expenditure and leucine kinetics were examined in Hereford x Friesian finishing beef steers. Estimates of whole body protein synthesis and protein oxidation were obtained from the specific radioactivity of free leucine in blood and of exhaled carbon dioxide during continuous infusions of [1-14C]leucine. Protein synthesis contributed a minimum of 0.19 to total heat production across all three intakes. The apparent efficiencies with which synthesized protein was retained were 0.28 between 1.6 M and M' and 1.04 between M' and fasting. The greater efficiency below M' reflected probable use of amino acids as energy sources during fasting, which would be spared as soon as feed was available. Nitrogen derived from protein oxidation made a minor contribution to urine N at both 1.6 M (0.45) and M' (0.36) but provided a significant proportion to the increment in urine N between intakes (0.68). Amino acid absorption, estimated indirectly as the sum of protein oxidation and protein retention, represented only 0.28 of N intake at M' and 0.38 at 1.6 M but the contribution to the increment in N intake between these two diet levels was greater (0.56). The estimated efficiency of utilization of absorbed amino acids between M' and 1.6 M was 0.45.
Original languageEnglish
Pages (from-to)457-65
Number of pages9
JournalBritish Journal of Nutrition
Volume57
Issue number3
Publication statusPublished - 1 May 1987

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Energy Metabolism
Eating
Leucine
Proteins
Fasting
Amino Acids
Maintenance
Urine
Thermogenesis
Red Meat
Carbon Dioxide
Radioactivity
Nitrogen
Diet

Keywords

  • Amino Acids
  • Animals
  • Body Temperature Regulation
  • Cattle
  • Eating
  • Energy Metabolism
  • Leucine
  • Male
  • Nitrogen
  • Proteins

Cite this

Effect of food intake on protein and energy metabolism in finishing beef steers. / Lobley, Gerald; Connell, A; Buchan, Vivien.

In: British Journal of Nutrition, Vol. 57, No. 3, 01.05.1987, p. 457-65.

Research output: Contribution to journalArticle

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N2 - The effects of progressive reduction in food intake from 1.6 X maintenance (1.6 M) to approximately maintenance (M') and then to zero (fasting) on energy expenditure and leucine kinetics were examined in Hereford x Friesian finishing beef steers. Estimates of whole body protein synthesis and protein oxidation were obtained from the specific radioactivity of free leucine in blood and of exhaled carbon dioxide during continuous infusions of [1-14C]leucine. Protein synthesis contributed a minimum of 0.19 to total heat production across all three intakes. The apparent efficiencies with which synthesized protein was retained were 0.28 between 1.6 M and M' and 1.04 between M' and fasting. The greater efficiency below M' reflected probable use of amino acids as energy sources during fasting, which would be spared as soon as feed was available. Nitrogen derived from protein oxidation made a minor contribution to urine N at both 1.6 M (0.45) and M' (0.36) but provided a significant proportion to the increment in urine N between intakes (0.68). Amino acid absorption, estimated indirectly as the sum of protein oxidation and protein retention, represented only 0.28 of N intake at M' and 0.38 at 1.6 M but the contribution to the increment in N intake between these two diet levels was greater (0.56). The estimated efficiency of utilization of absorbed amino acids between M' and 1.6 M was 0.45.

AB - The effects of progressive reduction in food intake from 1.6 X maintenance (1.6 M) to approximately maintenance (M') and then to zero (fasting) on energy expenditure and leucine kinetics were examined in Hereford x Friesian finishing beef steers. Estimates of whole body protein synthesis and protein oxidation were obtained from the specific radioactivity of free leucine in blood and of exhaled carbon dioxide during continuous infusions of [1-14C]leucine. Protein synthesis contributed a minimum of 0.19 to total heat production across all three intakes. The apparent efficiencies with which synthesized protein was retained were 0.28 between 1.6 M and M' and 1.04 between M' and fasting. The greater efficiency below M' reflected probable use of amino acids as energy sources during fasting, which would be spared as soon as feed was available. Nitrogen derived from protein oxidation made a minor contribution to urine N at both 1.6 M (0.45) and M' (0.36) but provided a significant proportion to the increment in urine N between intakes (0.68). Amino acid absorption, estimated indirectly as the sum of protein oxidation and protein retention, represented only 0.28 of N intake at M' and 0.38 at 1.6 M but the contribution to the increment in N intake between these two diet levels was greater (0.56). The estimated efficiency of utilization of absorbed amino acids between M' and 1.6 M was 0.45.

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