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.
1. Poorly defined carbohydrates in feeds and feed additives lead to problems in developing accurate and reliable rations that prove wasteful in animal performance and dollars spent. Readily digestible carbohydrates in animal feeds provide much needed nutritional energy, but can also lead to health issues if not properly balanced in the diet. A request was made of the American Feed Control Officials (AFCO) to develop feed labels that accurately define readily digestible carbohydrates such as sugars, starch, and fructans. In collaborative work with feed industry representatives, AFCO, and ARS scientists at the U.S. Dairy Forage Research Center worked to develop a nutritional definition for dietary starch. Such definitions are necessary in order to label feeds/feed additives correctly to represent their true nutritional value in a ration that will be fed to the livestock. Establishment of the dietary starch definition and the associated analysis will increase conformity of feed evaluation, which will improve interpretation of research results, allow standardization of feeding recommendations for different species, and increase the nutritional information available to nutritionists and consumers for use in maintaining the optimum performance and health of their animals.
2. Inaccurate starch determination methods lead to poorly developed rations that are not economical and do not result in peak animal performance. Starch is an important carbohydrate in animal feeds that can be used to provide needed energy, but has also been implicated in causing health disorders. Methods currently used for starch analysis typically underestimate the starch content of feeds. Accurate determinations of feed starch content allow nutritionists to formulate diets that efficiently and economically meet animal nutrient requirements while avoiding health disorders due to over- or underfeeding starch. An ARS scientist with the U.S. Dairy Forage Research Center developed a starch assay that was robust, increased ease of handling of samples, increased accuracy, and shortened the assay time. The assay is appropriate to measure "dietary starch", and will be subject to a collaborative study to determine its usefulness as an official method for regulatory and diet formulation purposes. Some commercial feed analysis and research laboratories are already using the assay. Application of the starch assay will improve the accuracy of values used by nutritionists and consumers to understand the nutritional value of feeds as they determine how to provide appropriate diets to the animals they feed.
3. On-farm use of portable near infrared reflectance diode-array (NIR-DA) sensors to measure moisture content in feedstuffs when mixing rations results in rations with optimal nutritional value for best animal performance. Changes in moisture of feeds can have substantial impact on the amount & composition of rations fed to dairy cows. Typical dairy rations contain whole-plant silages that are stored in open bunker silos. Changes in dryness of the crop harvested, & rain/snow events can change silage moisture on the day it is fed. When moisture increases, dry matter of the feed (containing the nutrients) is replaced by water. This changes the relative proportions of ingredients, resulting in rations with imbalanced nutrient ratios. We found a one-day change in the ration due to more moisture in silages can result in loss of >1.5 lbs milk/cow receiving the ration. In the lab, moisture was determined by loss of weight during drying for 24-48 h. This method does not work on the farm because ration adjustment must be made just before the ration is mixed. NIR-DA sensors rapidly detected changes in moisture content of feeds. ARS scientists at the Dairy Forage Research Center successfully calibrated a NIR-DA sensor to predict moisture in silages. It provided an almost instantaneous estimate of moisture after samples were collected & pressed into a glass bowl. The sensor was easy to use compared to on-farm drying methods that require attention for 2 to 10 min, with multiple weights of samples & calculation of results during the process. Farm personnel quickly adopted the technology to adjust rations routinely because the moisture data could be rapidly transferred to ration-mixing software that adjusted amounts of silage to be included. Large daily deviations in moisture (more than 10%-units) were often associated with rain/snow events. The technology improves cow performance & reduces health problems & excretion of excess nutrients associated with poorly balanced rations.
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.