1a. Objectives (from AD-416)
The objectives of this research are to: 1) Improve accuracy, reproducibility, and ease of measuring/estimating feed digestibility for fiber and protein for use in developing feeding strategies for improving animal performance; 2) Develop rapid methods for measuring feed qualities to improve on-farm precision of feeding; and 3) Establish methods to measure feed characteristics of nutritional relevance in dairy cattle diets.
1b. Approach (from AD-416)
The approaches for the diverse projects in this research will also be diverse. They will include evaluation of feed evaluation equipment and methods used on the farm and in the laboratory to measure specific feed components or their digestibility. We will compare the results of the experimental approaches to values for the feed components measured with standard measurement systems, or to digestibility data from studies with dairy cattle.
3. Progress Report
A3. A new method gives similar results to the standard method. Discovery was made that the new method became more consistent with a new vessel closure type; after further testing, the new closures were adopted. Samples for the forage processing comparison are delayed due to equipment issues, but will be pursued when the dried, frozen, and freeze-dried samples can be processed concurrently. 1.B. Evidence from comparisons of protease-based in vitro assays with in vitro assays based on inoculum prepared from rumen fluid indicated that proteases were insensitive to differences in degradability of feed proteins and will not be useful for feed evaluation. Near infrared reflectance spectroscopy (NIRS) calibrations were not yet attempted. Also, a rationale was developed for applying this approach to both soluble and insoluble proteins, in combination with an alternative assay to measure the compounds formed when proteins are broken down by the microbes in the rumen. Other research under this milestone assessed use of a rumen in vitro method that applied enzyme kinetic computations to determine rates of degradation of feed proteins by rumen microbes. This new approach was applied to typical protein supplements (different soybean meals) and tropical grasses that are grazed by Brazilian dairy cattle. 2.A. A research associate continues the research in this area. Samples (927) have been collected with 90% unground and wet-scanned, and 53% dried and ground-scanned. The dry predictions are being used to calibrate with the wet spectra. The project is behind schedule, but progressing well. 3.A. Additional evaluations of the starch method needed to meet the requirements of the Association of Official Analytical Chemists (AOAC) for the collaborative study protocol have been completed (linearity of analysis; interfering substances). Feed samples and a location to process them before sending them out have been arranged. Samples will be sent to participating laboratories once a committee of the AOAC approves the collaborative study protocol. 3.C. High-performance ion chromatography, phenol-sulfuric acid assays, and an enzymatic-colorimetric assay have been performed on extracts of multiple feeds to evaluate measurements of “sugar” content, completing the experimental portion of this sub-objective. 3. The experimental portion of a ring test has been completed with commercial and research laboratories to evaluate the repeatability of fiber digestibility measurements within and among laboratories over time.
1. An improved method has been developed to measure the quantity of feed protein escaping from the rumen. There are no reliable laboratory methods to measure feed protein escaping breakdown in the rumen, commonly referred to by farmers as “bypass protein”, which determines much of the value of feed protein for dairy cows. An ARS scientist in Madison, Wisconsin has developed an improved technique to measure dietary protein escape from the rumen. The method involves using rumen microbes (which are obtained by collecting digesta from the cow’s rumen) and incubating these microbes with the proteins being tested in the presence of chemicals that prevent microbial uptake of protein digestion products. Because the microbes cannot use the digestion products, there is a direct relationship of their rate of release with how fast protein is being degraded. Previously, no accounting was made of the formation of peptides (small protein fragments produced during protein breakdown). This research involved adapting a new chemical assay that measured peptides, as well as the other protein degradation products, and evaluating whether this new assay yields improved results. The method was applied to several kinds of soybean meal, one of the most important protein supplements fed to dairy cows. Overall, accounting for peptide formation reduced the variation, increased the observed protein degradation rate by 28%, and yielded estimates of protein escape for soybean meal that were similar to measurements made in living dairy cattle. These results were more reliable than those obtained using one of the most widely applied assays for evaluating proteins fed to dairy cows. This research indicated that the new method gives improved estimates of protein escaping the rumen for common feedstuffs.
Huhtanen, P., Ahvenjarvi, S., Broderick, G.A., Reynal, S.M., Shingfield, K.J. 2010. Quantifying Ruminal Digestion of Organic Matter and Neutral Detergent Fiber Using Omasal Sampling in Cattle--A Meta-Analysis. Journal of Dairy Science. 93:3203-3215.