Reprod. Nutr. Dev. 43 (2003) 117-129
DOI: 10.1051/rnd:2003010

Effect of intake on whole body plasma amino acid kinetics in sheep

Isabelle Savary-Auzeloux^{a, b}, Simone O. Hoskin^{a, c} and Gerald E. Lobley<sup>a

a</sup>  Rowett Research Institute, Bucksburn, Aberdeen, AB21 9SB, UK
^b  Present address: INRATheix, Clermont-Ferrand, 63122 St-Genès-Champanelle, France
^c  Present address: Institute of Food, Nutrition and Human Health, Massey University, Private Bag 11222, Palmerston North, New Zealand

(Received 23 January 2002; accepted 24 December 2002)

Abstract
While both the quantity and quality of food ingested are potent regulators of whole body protein metabolism in ruminants, little data are available on responses across a wide range of intakes. The current study examined the responses in whole body protein flux (PrF) to such intake changes and compared these with the responses across the hind-quarters (in a companion study). Six growing sheep (6-8 months, 30-35 kg) received each of four intakes of dried grass pellets (0.5, 1.0, 1.5 and 2.5 times maintenance energy; M) for a minimum of 7 days. At each intake, a mixture of U- ¹³C amino-acids (AA) was infused intravenously for 10 h. Arterial plasma and blood were obtained over the last 4 h of infusion and the concentrations and the enrichments of thirteen ¹³C labelled AA were determined. The absolute values for plasma Irreversible Loss Rate (ILR) but also converted PrF varied between the AA. PrF values were lower for histidine, methionine, aspartate, glycine and proline (range 68 to 174 g d ^-1 at 1.5 M) than for isoleucine, leucine, valine and glutamate (range 275 to 400 g d ^-1 at 1.5 M). These discrepancies may be explained by (1) the differential AA removal by the splanchnic tissues, (2) the de novo synthesis of the non-essential AA, (3) the transfer of AA from the erythrocytes or plasma to the tissues. The first two assumptions require further investigation whereas recent work has shown a minor role for AA transfers between erythrocytes and tissues. For most AA, ILR and PrF responded linearly to intake but curvilinear responses were observed for phenylalanine, lysine, leucine, isoleucine and tyrosine. These differences were not due to hind-quarter metabolism and may involve the digestive tract and liver.

Key words: intake / whole body / kinetics / ovine / amino acid

Correspondence and reprints: Isabelle Savary-Auzeloux
    e-mail: Savary@clermont.inra.fr

© INRA, EDP Sciences 2003