TECHNICAl NOTE: Effect of feeding free lysine or rumen-protected lysine on duodenal flows of essential amino acids in ruminants

Two ruminally and duodenally cannulated steers were used in a 2 × 2 crossover design to evaluate the effect of supplementation of free Lys or rumen-protected Lys on duodenal flows of essential AA (EAA). Dietary treatments were achieved by the supplementation of either free Lys or rumen-protected Lys to a basal diet composed of 50% alfalfa hay and 50% wet corn gluten feed. Chromium oxide (Cr2O3) was used as a digesta flow marker. Duodenal flow of DM was estimated by dividing the daily amount of (Cr2O3) dosed by the (Cr2O3) concentration in the duodenal samples. Duodenal flows of EAA were determined by multiplying the duodenal flow of DM by the concentration of the respective EAA in the duodenal sample. Duodenal flows of OM, ash, and N were determined in a similar fashion. Intakes of DM (P = 0.90), OM (P = 0.91), ash (P = 0.90), N (P = 0.89), and EAA (P ≥ 0.87) were similar for both treatments. Consequently, duodenal flows of DM (P = 0.17), OM (P = 0.14), ash (P = 0.20), N (P = 0.17), and EAA (P ≥ 0.22) did not differ. Supplementation of both Lys products resulted in similar duodenal flows of Lys.