Influence of rumen-protected lysine supplementation on growth performance and plasma amino acid concentrations in growing cattle offered the maize stalk silage/maize grain-based diet

The effects of rumen-protected lysine (RPLys) supplementation on growth performance, plasma amino acid (AA) concentrations and blood biochemical indices were investigated in a 84-d growth trial using 56 Limousin × Fuzhou F1 crossbred bulls (13 mo of age, average initial BW = 372.9 ± 22.4 kg) fed the maize stalk silage/maize grain-based diet. All animals were fed individually the same basal diet containing 500 g/kg maize stalk silage, 340 g/kg ground maize grain and 160 g/kg dry mixed concentrate (DM basis). Incremental amounts (0, 5, 10 or 15 g/d) of RPLys were added to the basal diet. Increasing supplemental RPLys level did not alter (P>0.05) dietary dry matter intake, but increased average daily gain (quadratic effect; P=0.036) and feed efficiency (quadratic effect; P=0.030) with maximum values achieved at 10 g/d RPLys supplementation. Supplementing dietary RPLys linearly (P=0.009) increased plasma Lys and quadratically (P=0.014) decreased plasma urea nitrogen, suggesting that added RPLys has been effectively utilized for tissue growth and Lys seems to be a first-limiting amino acid for growing cattle fed the maize stalk silage/maize grain-based diet. In summary, when growing cattle were fed maize silage/maize grain-based diets adequate in MP (MP = 780.9 g/d) but inadequate in Lys, their average daily gain and feed efficiency were promoted by dietary supplementation of RPLys.