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
1.A1. Develop rapid methods to define and quantify indigestible residue: A project scientist left ARS, so we redirected efforts to collect near infrared (NIR) spectra on alfalfa & grass forage samples that had digestibility information from lambs & an in vitro “artificial rumen” system. Indigestible residues are being determined using 96 h of fermentation in the in vitro system. Data provided minimal number of observations to calibrate a prediction equation so that rapid NIR spectral methods can be used; thus, the research effort has progressed at a limited pace. 1.A3. Improve in vitro fermentation systems to evaluate in vitro fiber digestibility: A system for purging pressure vessels (PV) with CO2 & allowing individual handling of PV was built & worked well. Evaluation of PV with the conventional fermentation method prompted more changes of the PV system. Comparable fiber digestion values at 30 h of fermentation were achieved with both systems. 1.B. In vitro methods to assess ruminal degradability of dietary proteins: Feed protein sources (solvent soybean meal, expeller soybean meal, blood meal, & corn gluten meal) for which in vivo estimates of rate & extent of ruminal protein degradation had been made, underwent a ruminal in vitro assay, using N-15 to distinguish microbial protein from undegraded feed protein & to allow calculation of feed protein degradation rate. This approach was very time-consuming & not appropriate for routine use or for calibrating more rapid in vitro or enzymatic assays. No progress occurred on chick growth assay. 2.A. Spectral analysis of undried, unground feeds with diode arrays, & 2.B. Develop hardware & software systems to automate on-farm collection, analysis & transfer of feed composition information: Near infrared reflectance spectra have been obtained on fresh & fermented alfalfa & whole-plant corn silages using diode-array & scanning monochrometer instruments. (See 3655-31000-021-02S 421 report). 2.B. Select optimal design, determine daily feed variation, develop editing algorithm: Daily variation in moisture of silage when fed to animals was measured. Variation in alfalfa silage was nearly 4 times that in corn silage. Algorithms are being developed to edit & smooth the variation so that moisture data can be used to adjust wet weight of silages mixed in rations. Changes in silage moisture alter the amount of dry matter (which contains the nutrients) if the same wet weight of silage is fed. A production trial was conducted to determine effects of variation in the moisture of silages on ration composition & dairy cow performance. (See 3655-31000-021-02S 421 report). 3.A. Establish reference method for starch analysis of animal feedstuffs: A definition was established for dietary starch, & a final version of the dietary starch assay was set. Preparation for the dietary starch analysis (selecting sample types, obtaining samples, & recruiting laboratories) has begun. 3.C. Establish analytical methods to measure dietary sugar in feedstuffs: Analyses of feedstuffs & purified samples were performed with 3 colorimetric methods & results compared to high performance ion chromatography results.
Broderick, G.A., Luchini, N.D., Reynal, S.M., Varga, G.A., Ishler, V.A. 2008. Effect on Production of Replacing Dietary Starch with Sucrose in Lactating Dairy Cows. Journal of Dairy Science. 91(12):4801-4810.