Influence of supplementation of growing diets enriched with rumen-protected methionine and lysine on feedlot performance and characteristics of digestion in Holstein steer calves

Objectives: The objective of this research was to evaluate the influence of rumen-protected methionine and lysine on growth performance of calf-fed Holstein steers during the initial 84-d feedlot phase and relate responses to measures of AA supply to the small intestine. Material and Methods: Seventy-two Holstein steer calves (128 +/- 9 kg) were blocked by weight and assigned to 12 pens (6 steers per pen). Steers were fed a diet based on steam-flaked corn formulated to provide 105% of theoretical MP requirements plus 0, 0.4, and 0.8% Smartamine ML (Adisseo, Alpharetta, GA; 55% L-lysine-HCl and 15% dl-methionine coated with a pH-sensitive polymer). Six Holstein steers (143 +/- 13 kg) with cannulas in rumen and proximal duodenum were used in a crossover design to evaluate characteristics of digestion and AA supply to the intestine of the basal diet plus 0 versus 0.8% Smartamine ML. Results and Discussion: Methionine and lysine supplementation did not affect DMI (P = 0.27) but enhanced ADG, gain efficiency (linear effect, P = 0.03), and estimated dietary NE (linear effect, P = 0.04). Amino acid supplementation increased (P < 0.01) intestinal supply of methionine and lysine and postruminal (2.4%, P = 0.03) and total-tract (3.2%, P < 0.01) N digestion. Metabolizable methionine and lysine supplies for the growth performance trial were associated (R-2 >= 0.88) with the efficiency of ME for maintenance and gain. Implications and Applications: Supplementation with rumen-protected methionine and lysine may enhance gain efficiency and dietary energetics of growing Holstein calves during the early growing phase. The magnitude of the response is likely dependent on the otherwise general adequacy of nonspecific MP.