| Intestinal and total tract digestibility of crude protein (CP) and amino acids in rumen undegraded protein (RUP-AA) in 5 corn silage hybrids were measured using the mobile bag technique (MBT). Two in vitro methods, the modified three-step procedure (TSP) and an in vitro procedure (IVP) developed by Sapienza Analytica, LLC (Slater, IA), were further evaluated to determine digestibility of RUP-AA in corn silage. Intestinal digestibility of RUP-AA in corn silage varied from 24 to 59%, indicating differences in intestinal digestibility among AA. The TSP and IVP tended to under predict RUP-AA digestibility compared with the MBT. Consequently relationships between the in vitro methods and the MBT for RUP-AA digestibility were poor. The TSP and IVP tended to be better predictors of total tract digestibility compared with the MBT. These results suggest the TSP and IVP are accurate in vitro methods to estimate total tract digestibility of CP and AA. |
