Methods To Analyze Feeds For Nitrogen Fractions And Digestibility For Ruminants With Application For The Cncps
To improve the ability to predict amino acid flows in ruminants, which will enhance the efficiency of use of feed nitrogen (N), methods to better predict metabolizable protein (MP) and amino acid supply need to be developed. The objectives of this study were (1) to evaluate and improve the efficiency of precipitable true protein assay to understand the peptide profile that is chelated to better predict the supply of those components to support the MP supply of the cow; (2) to evaluate Streptomyces griseus assay as indicator for AA profile of MP supply; and (3) evaluate variation with published total digestion assays and make improvements to better estimate intestinal protein digestion of feeds for ruminants. Throughout, methods were evaluated or developed with commercial labs in mind so values could routinely be analyzed for use in the CNCPS. The efficiency of the precipitated true protein (PTP) assay was improved with tungstic acid (TA) or stabilized TA filtered on 1 or 6 [MICRO SIGN]m filters (P < 0.05) but was time consuming as were ultrafiltration devices. Nonprotein N as assayed contains substantial quantities of amino acids and peptides. The Strep. griseus assay will predict rumen degradation of N but will not predict AA supply or digest carbohydrates and fiber. An in vitro (IV) assay to estimate intestinal protein digestion for ruminants was developed using an enzyme mix of trypsin, chymotrypsin, lipase and amylase at activities found in sheep digesta to replace pancreatin, reduced sample loss by eliminating the use of bags by employing Erlenmeyer flasks, utilized small pore size filter papers to further improve recoveries of undigested feed N and corrects for microbial contamination with corn silage ND. Acid detergent insoluble (ADI) N is digestible; thus, undigested N from the IV intestinal assay more accurately represents the protein C fraction than does ADIN given the more physiological conditions of rumen incubation and enzyme exposure. The IV assay provides a method, adoptable by commercial labs, to evaluate intestinal digestibility of ruminant feeds to better predict the MP and amino acid supply for input into the CNCPS.
ruminants; nitrogen fractions; intestinal digestion; soluble protein
Van Amburgh, Michael E
Overton, Thomas R; Barbano, David Mark
Ph. D., Animal Science
Doctor of Philosophy
dissertation or thesis