Abstract:
The passage of amino acids into the duodenum and the levels of amino acids in jugular plasma were studied (a) in lambs given a supplement of casein with or without formaldehyde treatment, and (b) in sheep given concentrate diets containing treated or untreated peanut meal at both a low and a high level of dietary protein. When casein in the diet was treated with formaldehyde, losses of individual amino acids due to degradation in the rumen were substantially reduced or prevented so that the amounts reaching the small intestine were substantially increased. This increase in supply of amino acids, which was associated with an increase in the rate of liveweight gain, caused an increase in the plasma levels of most amino acids. However, lysine levels tended to fall, and this resulted in marked reductions in the molar proportion of lysine. When sheep were given formaldehyde-treated peanut meal, the amounts of the individual amino acids reaching the small intestine were greater than when untreated peanut meal was given. When the meal in the higher protein diet was treated, the losses due to degradation were again largely prevented. As amino acid supply to the small intestine increased, the plasma levels of most of the individual amino acids decreased to a minimum and then increased when supply exceeded demand. The molar proportion of lysine decreased when peanut meal in the higher protein diet was treated. An increase in plasma s-N-methyllysine level was characteristic of formaldehyde treatment of dietary protein. Changes in arginine levels tended to be inversely related to changes in total amino acid levels.