Net Amino Acid Absorption in Steers Fed Alfalfa Hay Cut at Two Stages of Maturity

Twelve Holstein steers with initial weights of 130 to 202kg were assigned to a 63-day performance trial on a completely randomized basis for two maturities of alfalfa hay. They were fed at 110% of voluntary consumption. At the end of the performance trial, digestion and nitrogen balance information was obtained on the same steers. Two steers from this group and one additional steer were employed to measure in nine separate 48-h experiments, blood flow by the Doppler shift and telemetry technique and net amino acid absorption from portal-carotid differences. Mean portal blood flow was 39.2 ml/min per kg body weight. Differences in blood flow between treatments were not significant. Advanced hay maturity decreased voluntary intake, feed efficiency, and gain. Further, digestibility of all proximate fractions were lower. Essential, nonessential, and total amino acid absorptions were reduced by advanced maturity to a much greater degree than could be attributed to differences in intake of digestible protein. Approximately five times as much amino acid was absorbed from good quality as from reduced quality alfalfa hay.