Lysine utilization by growing pigs: simultaneous measurement of protein accretion and lysine oxidation

Abstract

Nitrogen retention and lysine oxidation were measured in growing pigs given diets which supplied 0,0-2 or 08 of the lysine requirement, with other amino acids in relative excess. Eight groups of three female littermate pigs were used: one of each group was given each of the three diets. In half the pigs (four groups) N retention was measured at body weights (W) of approximately 25,35 and 45 kg. The other four littermate groups of three pigs were given the same three diets; when they reached 35 kg W they were given a continuous (6 h) primed infusion of ~-[6-~H]lysine. Lysine oxidation was estimated from the production of tritiated water. Rates of both N retention and lysine oxidation increased significantly with lysine intake; mean values (g/kg W@75 per d) for the three diets respectively were for N retention, 0.00, 0.32 and 1.22, and for lysine oxidation 0051, 0.058 and 0.078. From the N balance results (assuming a constant lysine concentration in body protein) the efficiency of utilization of absorbed lysine was estimated to be 085; from the oxidation results (assuming lysine absorbed but not retained is oxidized) the estimate was 095.

Twenty-four–hour oral tracer studies with l-[1-13C]lysine at a low (15 mg • kg−1 • d−1) and intermediate (29 mg • kg−1 • d−1) lysine intake in healthy adults

“…Hence, if lysine balance can be achieved at an intake of 29 mg·kg Ϫ1 ·d Ϫ1 , as our study suggests, then the efficiency of utilization of dietary lysine approaches 100% (ie, the intake needed to balance obligatory losses) at that intake. This is also consistent with the data from animal experiments that showed that when lysine is limiting in the diet it is particularly well conserved (20,26,27).…”

“…Above this physiologic requirement intake, oxidation increases with increased amino acid intake. In growing pigs, lysine oxidation did increase when diets supplied 0, 0.2, and 0.8 of the lysine requirement but even in this case the changes in lysine oxidation amounted to only 0.38 g/d with an 8.8-g change in lysine intake (20). Hence, our findings in healthy adults are consistent with the view that the 2 test lysine intakes studied (low and intermediate) fall in the range approximating a minimum physiologic requirement value and below.…”

Dietary deficiencies of single amino acids: Whole-body amino acid composition of adult rats

“…In the case of amino acid deficiency the first adaptation is to reduce the oxidation of the limiting amino acid (Mnilk et al 1996;Moehn et al 2003). Further adaptations might then involve alterations in the relative rates of synthesis or breakdown (or both) of different proteins according to their amino acid composition, such that the accretion of a protein rich in the deficient amino acid might be synthesized more slowly, or broken down faster, to make more of the limiting amino acid available for the accretion of those proteins which contain less of that amino acid.…”

Reviewing the low efficiency of protein utilization in heavy preruminant calves – a reductionist approach

“…Although this reduction is in accordance with the decreasing amino acid utilization for protein accretion with increasing stage of maturity [6], the efficiency in heavy preruminant calves is extremely low compared with other species. In pigs, for example, gross efficiencies of protein utilization of 60% up to as high as 81% were reported [7][8][9][10]. For a sound comparison of efficiencies, however, different species should be compared at a similar stage of maturity, and marginal efficiencies, rather than gross efficiencies, should be compared.…”