Methods to Evaluate Rumen Protected Lysine for Dairy Cows

Abstract

There are many rumen protected amino acid products available for dairy cattle feeding. However, feed formulation programs require values related to rumen solubility, rate of disappearance in the rumen and total tract digestibility and often such values are not available. In vivo testing procedures are complex, time consuming and expensive. This study was conducted to determine if a newrapid, lower cost in vitro method developed for feed ingredients could be applied to a rumen protected lysine product (DairynatLys-30®, Jefo Nutrition Inc). In vivo determination of the rapidly solubilized protein fraction, rate of degradation of the slowly solubilized fraction and total tract digestibility studies were compared to the in vitro method in use in many ingredient analysis laboratories for feed ingredients such as forages, protein supplements and grains. Results showed that the rapidly soluble fraction (8.33% and 8.66% of total N for in vivo and in vitro methods) and rates of disappearance in the rumen (2.64%/h and 2.43%/h for in vivo and in vitro procedures) compared favorably between the two methods for the rumen protected product. Total tract digestibility values were slightly higher (84.4%) with the in vivo method used than with the in vitro method (75.9%), and both are in the expected calculated range of digestibility of 80%. In conclusion the in vitro method appears to be an acceptable alternative for evaluating rumen protected amino acids.