Four dairy steers were allotted to four lysine infusion levels in a 4 × 4 latin square design and fed an 11.5% crude protein (90% dry matter (DM)) diet continuously (10-min intervals every 24 hr). Lysine hydrochloride equivalent to 0.0, 3.0, 6.0, and 9.0 g lysine per day was infused per abomasum. When 9 g lysine were infused per day, the percent of absorbed nitrogen (N) retained was significantly (P < 0.05) reduced; urinary N excretion as a percentage of N intake and plasma-free lysine were increased significantly compared with the other three infusion treatments. The infusion of 9 g lysine per day apparently exceeded the body tissue requirements for this amino acid and the excess N was excreted in the urine. A possibility of lysine being limiting (0.28% lysine of a 100% DM diet) was apparently offset by the synthesis of lysine by rumen microorganisms, which increased the dietary lysine two- to threefold. Increased levels of infused lysine did not result in a linear increase of lysine in the abomasum. With 3 g per day lysine infusion rumen ammonia and N retentions were high. However, a smaller amount of N reached the abomasum with steers on this treatment.
Amino acid pattern of rumen microorganisms in cattle fed mixed diets—An update
