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United States Department of Agriculture

Agricultural Research Service

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Location: Cell Wall Biology and Utilization Research

2012 Annual Report

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:
The progress reported here relates to research Objective 1. Through the course of this project, a number of methods have been developed or evaluated to provide improved methods of feed analysis for commercial application and research. Two advances occurred in the area of neutral detergent fiber digestibility (NDFD) by ruminal microbes. 1) A novel in vitro fermentation system was developed that gives values similar to the most commonly used system. This system can be used with less handling of samples in fermentations where low-speed centrifugation of samples can be performed without sample transfer. 2) A ring test provided definitive information on within- and between-lab variation, which stimulated a key industry group to monitor NDFD values in its check sample system. Additionally, the impact of sample processing methods before measurement of NDFD was characterized. An improved laboratory procedure for measuring rumen protein degradability was developed that accurately reflected differences between protein sources that were provided to lactating cows. Work progressed on development of near infrared reflectance spectroscopy calibrations for rapid analysis of undried and unground feed samples, which will improve the on-farm utility of feed analyses. A robust reference method for starch in animal feeds has been developed and will be tested in a collaborative study through the Association of Official Analytical Chemists (AOAC) to become an official method (appropriate for regulatory purposes). The technology of this method has already been transferred to, and is widely used by commercial feed analysis laboratories serving the livestock, feed, and forage grower industries in the U.S. This new method for starch analysis more accurately reflects available energy to dairy cattle. It has given nutritionists and dairy farmers a better tool to fine-tune rations with optimal energy levels that help dairy cows remain healthy and productive. Methods of sugar analysis were evaluated. A nutritionally relevant carbohydrate fraction for dairy cows was identified. Work continues with the AOAC as it strives to identify methods to measure monosaccharides, sucrose, lactose, and maltose in feeds fed to multiple livestock species.

4. Accomplishments
1. Evaluation of fiber digestibility assays leads to industry effort to improve consistency of commercial laboratory procedures. Tens of thousands of fiber digestibility analyses are purchased each year by nutritionists, farmers, and feed and seed companies to determine the nutritional and commercial value of forages and other feeds given to cattle. In a first step to address the confusion caused by variability and to move toward better quality control of fiber analysis, ARS scientists in Madison, Wisconsin evaluated the variability in fiber digestibility values that were generated by commercial and research feed analysis laboratories. As a result of this work, the National Forage Testing Association (NFTA), which is a collaborative enterprise of the National Hay Association, American Forage and Grassland Council, and Feed Analysis Laboratories, has begun to monitor fiber digestibility values determined on samples sent by participating laboratories. This is a critical first step toward improving the consistency of these values and, in turn, enhancing the utility of the values to the farmers, ranchers, nutritionists, veterinarians, and forage producers who use the information to assess the quality and value of forages for livestock feeding.

2. Canola meal is a better source of protein for dairy cattle than soybean meal. In 2011, ARS scientists in Madison, Wisconsin developed a laboratory procedure to evaluate dietary proteins to help determine the protein value of feeds for dairy cows. Protein that escapes the rumen is more efficiently utilized by the cow to make milk, not manure. Analysis of a large set of canola meal samples collected from 12 production facilities revealed an average rumen-undegraded protein value of 42%, versus an average of 33% for soybean meal, showing that the protein in canola meal would be a more efficiently used by dairy cows. In a follow-up lactation study, canola meal replaced equal amounts of protein from soybean meal in dairy cow diets. Milk and protein yields increased; milk urea concentration (reflecting inefficient protein utilization) was reduced. Concentrations of ammonia and branched-chain volatile fatty acids (which are produced from protein degradation in the rumen) were also reduced when canola meal replaced soybean meal in the diet. These results confirmed that canola meal is a more effective protein source for dairy cattle than soybean meal, the standard protein supplement currently fed to U.S. dairy cows. The results may cause dairy producers to consider canola meal as an alternative protein source that would also reduce nitrogen excretion by the cow and, thus, lessen the environmental impact of milk production.

Review Publications
Hall, M., Mertens, D.R. 2012. A ring test of in vitro neutral detergent fiber digestibility: Analytical variability and sample ranking. Journal of Dairy Science. 95(4):1992-2003.

Krizsan, S.J., Broderick, G.A., Promkot, C., Colombini, S. 2012. Effects of alfalfa silage storage structure and roasting corn on ruminal digestion and microbial CP synthesis in lactating dairy cows. Animal. 6:624-632.

Last Modified: 06/24/2017
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