ARS | Publication request: Rumen-degradable protein in roll conditioned or macerated legume hays and silages estimated by in situ kinetics vs. alternative methods

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 24, 2011
Publication Date: July 1, 2011
Repository URL: http://handle.nal.usda.gov/10113/56464
Citation: Grabber, J.H., Coblentz, W.K., Broderick, G.A. 2011. Rumen-Degradable protein in roll conditioned or macerated legume hays and silages estimated by in situ kinetics vs. alternative methods. Crop Science. 51:1832-1839.

Interpretive Summary: Alfalfa is the fourth most widely grown crop in the United States and it is potentially a rich source of protein for ruminant livestock such as dairy cattle. Unfortunately, excessive protein breakdown during harvesting, storage, and the initial digestion of alfalfa in the rumen of cattle can limit milk production and lead to greater excretion and loss of ammonia from manure to the environment. As a result, alfalfa is often substituted with feeds possessing more stable proteins, but this can increase feed costs, impair animal health, or increase the dependence of farms on potentially polluting and energy-intensive row crops. In the future, alfalfa engineered to produce protein-binding substances, known as polyphenols, should provide a sustainable approach for improving protein use by dairy cattle and other livestock. In this study, we found that the presence of polyphenols in forage legumes, conditioning by maceration rather than by rolls, and conservation as hay rather than as silage reduced concentrations of rumen degradable protein from the excessive levels often observed in alfalfa. Maceration acted synergistically with polyphenols to limit the rumen degradability of protein in hays but not in silages. Since incubating forages in the rumen is often too time consuming, difficult, or costly for commercial feed analysis laboratories, we identified three simpler degradability assays that worked reasonably well for predicting forage protein breakdown in the rumen. The results of this and ongoing studies will aid plant scientists, agronomists, and nutritionists as they develop polyphenol containing alfalfa for production and feeding on dairy farms.

Technical Abstract: Alternatives to the in situ method for estimating rumen-degradable protein (RDP) in diverse forage legumes should be validated. In this study, RDP in roll conditioned or macerated silages and hays of Medicago, Lotus, and Trifolium species with differing polyphenol compositions were estimated from in situ degradation kinetics, a rumen microbial inhibitor in vitro assay, a 10-h in situ incubation, the Cornell Net Carbohydrate and Protein System, and a 16-h in vitro Streptomyces griseus protease digestion. Forage species, conditioning and conservation methods influenced RDP estimates. In situ kinetic RDP could be ranked or in some cases accurately predicted by other RDP methods, but the protease method performed poorly for macerated forages.