A collaborative study was conducted to evaluate the repeatability and reproducibility of an extension of AOAC Official Method 991.20, Nitrogen (Crude) in Milk, to animal feed, forage (plant tissue), grain, and oilseed materials. Test portions are digested in an aluminum block at 420°C in sulfuric acid with potassium sulfate and a copper catalyst. Digests are cooled and diluted, and concentrated sodium hydroxide is added to neutralize the acid and make the digest basic; the liberated ammonia is distilled by using steam distillation. The liberated ammonia is trapped in a weak boric acid solution and titrated with a stronger standardized acid, hydrochloric acid; colorimetric endpoint detection is used. Fourteen blind samples were sent to 13 collaborators in the United States, Denmark, Sweden, Germany, and the United Kingdom. Recoveries of nitrogen from lysine, tryptophan, and acetanilide were 86.8, 98.8, and 100.1%, respectively. The within-laboratory relative standard deviation (RSDr, repeatability) ranged from 0.40 to 2.38% for crude protein. The among-laboratories (including within-) relative standard deviation (RSDR, reproducibility) ranged from 0.44 to 2.38%. It is recommended that the method be adopted First Action by AOAC INTERNATIONAL. A lower concentration (1% H3BO3) of trapping solution was compared with the concentration specified in the original protocol (4% H3BO3) and was found comparable for use in an automatic titration system in which titration begins automatically as soon as distillation starts. The Study Directors recommend that 1% H3BO3 as an optional alternative to 4% boric acid trapping solution be allowed for automatic titrators that titrate throughout the distillation.

A method for determining crude fat in animal feed, cereal grain, and forage (plant tissue) was collaboratively studied. Crude fat was extracted from the animal feed, cereal grain, or forage material with diethyl ether by the Randall method, also called the Soxtec method or the submersion method. The proposed submersion method considerably decreases the extraction time required to complete a batch of samples. The increase in throughput is very desirable in the quest for faster turnaround times and the greater efficiency in the use of labor. In addition, this method provides for reclamation of the solvent as a step of the method. The submersion method for fat extraction was previously studied for meat and meat products and was accepted as AOAC Official Method 991.36. Fourteen blind samples were sent to 12 collaborators in the United States, Sweden, Canada, and Germany. The within-laboratory relative standard deviation (repeatability) ranged from 1.09 to 9.26% for crude fat. Among-laboratory (including within) relative standard deviation (reproducibility) ranged from 1.0 to 21.0%. The method is recommended for Official First Action.

A number of analytical methods for constituents commonly measured in distillers dried grains (DDG) are practiced in laboratories serving the agricultural sector. A large interlaboratory variability among results has been observed in the industry. Methods for moisture, crude fat, and crude fiber are empirical, thus part of this variability can be attributed to the use of different methods of analysis. A study was organized and supported by the American Feed Industry Association, the Renewable Fuels Association, and the National Corn Grain Association to evaluate the efficacy, applicability, and the intralaboratory variation of a number of methods for moisture, crude protein, crude fat, and crude fiber in DDG with solubles (DDGS). The moisture methods included in the study are AOAC 930.15, AOAC 934.01, AOAC 935.29, AOAC 2003.06, and National Forage Testing Association (NFTA) 2.2.2.5; the crude protein methods studied are AOAC 990.03 and AOAC 2001.13; the crude fat methods studied are AOAC 945.16, AOAC 954.02, AOAC 2003.05, and AOAC 2006.06; and the crude fiber methods studied are AOAC 978.10 and AOCS Ba 6a-05. A second study was undertaken to assess existing interlaboratory variation of the same methods in 23 laboratories. Based on the results of these studies, the sponsoring associations established recommended reference methods for use in commercial trade of DDGS. The reference methods selected are NFTA 2.2.2.5 for moisture, AOAC 990.03 and AOAC 2001.11 for crude protein, AOAC 945.16 for crude fat, and AOAC 978.10 for crude fiber.

AOAC Official Method 942.05, Ash in Animal Feed, has been applied in feed laboratories since its publication in the Official Methods of Analysis in 1942. It is a routine test with renewed interest due to the incorporation of "ash values" into modern equations for the estimation of energy content of dairy feed, beef feed, and pet food. As with other empirical methods, results obtained are a function of the test conditions. For this method, the critical conditions are the ignition time, ignition temperature, and any other furnace or weighing conditions. Complete ignition can be observed by the absence of black color (due to residual carbonaceous material) in the ash residue. To investigate performance of AOAC 942.05, 15 samples were chosen to be representative of a wide range of feed materials. These materials were tested at the conditions of AOAC 942.05 (ignition at 600 degrees C for 2 h) and similar or more rigorous conditions. The additional conditions investigated included: 600 degrees C for 4 h; 600 degrees C for 2 h, cool, and ignite 2 additional h; 600 degrees C for 2 h, cool, wet, dry, and ignite 2 additional h; 550 degrees C for 6 h; 550 degrees C for 3 h, cool, and ignite 3 additional h; and 550 degrees C for 3 h, cool, wet, dry, ignite 3 additional h. Results for all other conditions investigated were found to be significantly different from the current AOAC Method 942.05. All ignition conditions were significantly different from each other except two: 550 degrees C for 3 h, cool, ignite 3 additional h; and 550 degrees C for 3 h, cool, wet, dry, and ignite 3 additional h. Recommendations for modification to AOAC Official Method 942.05 are suggested based on statistical analysis of the data and a review of the literature.

A method for determining crude fat in animal feed, cereal grain, and forage (plant tissue) was collaboratively studied. Crude fat was extracted from the animal feed, cereal grain, or forage material with hexanes by the Randall method, also called the Soxtec method or the submersion method. The use of hexanes provides for an alternative to diethyl ether for fat extractions. The proposed submersion method considerably decreases the extraction time required to complete a batch of samples compared to Soxhlet. The increase in throughput is very desirable in the quest for faster turnaround times and the greater efficiency in the use of labor. In addition, this method provides for reclamation of the solvent as a step of the method. The submersion method for fat extraction was previously studied for meat and meat products and was accepted as AOAC Official Method 991.36. Fourteen blind samples were sent to 14 collaborators in the United States, Sweden, Canada, and Germany. The within-laboratory relative standard deviation (repeatability) ranged from 1.23 to 5.80% for crude fat. Among-laboratory (including within) relative standard deviation (reproducibility) ranged from 1.88 to 14.1%. The method is recommended for Official First Action.

Several technologies have been proposed to characterize the nutrient release patterns of slow-release fertilizers (SRF) and controlled-release fertilizers (CRF) during the last few decades. These technologies have been developed mainly by manufacturers, and are product-specific, based on the regulation and analysis of each SRF and CRF product. Despite previous efforts to characterize SRF and CRF materials, no standardized, validated method exists to assess their nutrient release patterns. However, the increased production and distribution of these materials in specialty and nonspecialty markets requires an appropriate method to verify product claims and material performance. A soil incubation column leaching procedure was evaluated to determine its suitability as a standard method to estimate nitrogen (N) release patterns of SRFs and CRFs during 180 days. The influence of three soil/sand ratios, three incubation temperatures, and four soils on method behavior was assessed using five SRFs and three CRFs. In general, the highest soil/sand ratio increased the N release rate of all materials, but this effect was more marked for the SRFs. Temperature had the greatest influence on N release rates. For CRFs, the initial N release rates and the percentage N released/day increased as temperature increased. For SRFs, raising the temperature from 25 to 35 degreesC increased initial N release rate and the total cumulative N released, and almost doubled the percentage released/day. The percentage N released/day from all products generally increased as the texture of the soil changed from sandy to loamy (lowa>California>Pennsylvania>Florida). The soil incubation technique was demonstrated to be robust and reliable for characterizing N release patterns from SRFs and CRFs. The method was reproducible, and variations in soil/sand ratio, temperature, and soil had little effect on the results.

Accurate determination of the moisture (water) content in individual feed ingredients and mixed feeds is critical throughout the feed industry. Most analytical methods used to determine apparent water content of feedstuffs are empirical, estimating water by evaporation and loss of weight on drying (oven drying methods). These methods differ greatly in effectiveness, resulting in bias. Bias associated with measuring the water content of feedstuffs is a concern not only because of the lack of confidence in the moisture value itself, but also because moisture determinations affect accurate quantification and expression of other nutrient values. Methods for determining moisture in feeds have frequently been borrowed from the cereal, forage, or other applications without validating the extension of the method. Methods such as Karl Fischer titration measure water by direct comparison to a calibration standard for water and can be used as reference methods for the evaluation of empirical methods. The objective of this paper is to review methods for determining moisture, review comparisons among moisture methods for various feedstuffs, make recommendations for a reference method, and make general recommendations toward improving the results of moisture testing. The need to evaluate and improve moisture methods and standardize practices in laboratories is evident from this study. It also is evident that the methods appropriate for a specific feed ingredient or feed should not be extended to all feeds without proper validation to the new matrices. Part of the validation for empirical methods should be comparison to Karl Fischer or other the direct methods. It also is recommended that the results obtained using oven methods not be termed "moisture;" rather, they should be termed "loss on drying," and the drying conditions should become part of the term.

In a comparative study of the Karl Fischer method with oven methods for determination of water in forages and animal feeds, oven methods yielded the following relative recoveries (expressed as a percentage of the recovery obtained by the Karl Fischer method) for hay, haylage, and corn silage, respectively: (1) drying at 135°C for 2 h (AOAC 930.15), 113,162, and 133%; (2) drying at 104°C for 3 h (AOAC 935.29), 96,122, and 113%; and (3) drying at 104°C for 6 h, 97, 129, and 117%. Relative recoveries for nonurea-containing and urea-containing feed, respectively, were as fol lows: (1) drying at 135°C for 2 h (AOAC 930.15), 116 and 2746% (2) drying at 104°C for 3 h (AOAC 935.29), 88 and 239%; (3) drying at 95°C for 5 h under vacuum (AOAC 934.01), 83 and 727% (4) drying at 104°C for 6 h, 90 and 427%; and (5) drying at 110°C for 3 h, 94 and 425%. Preliminary near-infrared reflectance calibrations for water (moisture) based on the Karl Fischer method were promising (r2 = 0.98; standard error of calibration = 0.20).