Effect of abomasal infusion of aspartate on nitrogen balance and plasma amino acids in Holstein steers.

We investigated the effect of abomasally infused aspartate (Asp) on N balance and plasma amino acids in steers. Four ruminally cannulated Holstein steers (180 kg) housed in metabolism crates were used in an experiment designed as a 4 x 3 Youden square. Steers received continuous abomasal infusions of water or water containing 40 or 80 g Asp/d. Steers were fed twice daily a diet containing 473 g/kg corn, 463 g/kg alfalfa hay and 52 g/kg soybean meal at levels near ad libitum intake. Abomasally infused Asp had no effect on N balance. Infusion of 80 g Asp/d increased (P < 0.05) plasma concentrations of Asp, glutamate and alanine. Metabolism of Asp by gut tissues probably prevented the large change in plasma concentration of Asp that seems necessary to trigger hormonal responses. We conclude that abomasal supplementation of steers with up to 80 g/d of Asp does not enhance performance.