EFFICIENCY OF UTILIZATION OF ABSORBED AMINO-ACIDS IN GROWING LAMBS GIVEN FORAGE AND FORAGE - BARLEY DIETS

The efficiency of utilization of absorbed essential amino acids (AA) w as studied in wether lambs (35 to 40 kg live weight) given dried grass and dried grass : barley pelleted diets over an intake range from mai ntenance (M) to 2.5 M energy intake. Each animal was prepared with a d uodenal and ileal simple (T-shaped) cannula for the collection of dige sta entering and leaving the small intestine and with a catheter into the abomasum for the infusion of digesta phase markers (Ru-103 phenant hroline and Cr-51 ethylene diamine tetra acetic acid). The efficiencie s of utilization of total AA and individual essential AA (EAA) were ca lculated from the ratios of the regressions describing AA retention pe r unit nitrogen (N) intake (assessed using the N retention data obtain ed in the present study and the AA composition of N retention derived during an accompanying comparative slaughter experiment) and AA absorp tion per unit N intake. These ratios for total EAA were 0.5 for the gr ass diet and 0.59 for the grass plus barley diet. Values for individua l EAA ranged from 0.32 for threonine in sheep given the grass diet to 0.88 for arginine in sheep given the grass : barley diet. Whilst the r atios for total and individual EAA were generally higher for the grass : barley diet the very wide 95% confidence limits associated with the se derived values make any between-diet or between-EAA comparisons equ ivocal. The data appear to support the introduction by the Agricultura l and Food Research Council (1992), of a scaling factor to reduce the high efficiency of utilization of AA used previously.