Farm Animal Metabolism and Nutrition

‘endogenous’ provision via arterial blood. In
addition to tissue amino acid supply
originating from the plasma pool, studies in
muscle and mammary gland have identified
the possible role of peptides in ensuring
sufficient balance of amino acids for tissue
synthetic requirements. This concept has
been extended more recently to include
plasma proteins, specifically the liver export
proteins, as further ‘currency’ in the
exchange between tissues. The relative

importance of these different sources and

the mechanisms involved in the control of

amino acid flux to specific tissues are

unknown. An understanding of these pro-

cesses and the fundamental questions con-

cerning regulation of the anabolic and

catabolic fate of amino acids within tissues

is essential if we are to improve our ability

to formulate rations to meet the require-

ments of both ruminant and non-ruminant

livestock.

Inter-organ Amino Acid Flux 59

Fig. 3.2.Protein turnover rates (g day^1 ) in different body components of young weaned lambs. Amino acid
(AA) flux from the AA pool to a particular tissue represents protein synthesis, whereas flux into the AA pool
represents protein degradation; Ps represents body protein synthesis. Reproduced with permission from
MacRae (1993).

References

Agricultural and Food Research Council (1984) Report of the Agricultural Research Council Working
Party on the Nutrient Requirements of Ruminants. Commonwealth Agricultural Bureau, Farnham
Common.
Agricultural Research Council (1980) The Nutrient Requirements of Ruminant Livestock, Number 2
Ruminants. Commonwealth Agricultural Bureau, Farnham Common.