Formaldehyde treatment of concentrate diets for sheep. III.* Absorption of amino acids from the small intestine

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Abstract
The effects of formaldehyde treatment of barley/soybean meal diets on the flow of amino acids to the small intestine, their release and absorption there, and their levels in jugular plasma were studied at four protein levels in fistulated crossbred sheep. There were substantial losses of amino acids during passage through the stomach at the highest protein level which were prevented by formaldehyde treatment; the net gains of amino acids observed with the lower protein diets were enhanced by treatment. There were no statistically significant effects of treatment on the proportions of the individual amino acids apparently absorbed in the small intestine, but a tendency for the values to decrease for the highest protein diet suggested that this diet was overtreated. This was confirmed by calculation of the true digestibilities in the small intestine: the true digestibility of true protein in the small intestine was 0.74 for the treated high protein diet and 0.81 for all the other diets. Of the individual amino acids, only lysine was adversely affected by treatment; however, despite reduced intakes, the net absorption of lysine was equal to or greater than that achieved with the untreated diets at all but the lowest protein level. Formaldehyde treatment was associated with substantial increases in the concentration of ε-N-methyl-lysine in plasma. As the amount of protein absorbed from the small intestine increased to about 110 g/day, the concentrations in plasma of the amino acids normally present in protein declined to a minimum or remained steady; thereafter, except for lysine, the concentrations increased. ____________________ *Part II, Aust. J. Agric. Res. 28: 1069 (1977).