Committee on Feeds, Fertilizers, and Related Agricultural Topics

Abstract

Eight topics of study in the feed area are discussed within this report. Topics with potential collaborative study protocols pending upon completion of data collection are "Loss on Drying for 3 Hours at 105° C," and an SPE/LC method for determining vitamin A. A topic being reinvestigated is AOAC Official Method 942.05, Ash of Animal Feed. Five collabora-tive studies, which are underway or in some stage of report review , are discussed in the Selected Topics Section. Loss on Drying for 3 Hours at 105°C-New Method The National Forage Testing Association's (NFTA) Moisture Task Force investigated the reproducibility, accuracy, and applicability of various oven moisture methods for estimating moisture in forages (personal communication, report to NFTA Board of Directors). A round robin test was conducted to gather data. Two alfalfa hay, 2 grass hay, and 2 corn silage materials were sent to each of 8 laboratories. All materials came from previous NFTA Proficiency Testing materials. Each laboratories ran moisture by 3 oven methods: 105° C for 3 h, 105° C for 6 h, and 135° C for 2 h. The Karl Fischer moisture technique used is now AOAC 2001.12. Comparison of oven methods.-Analysis of variance for each sample revealed that laboratories and methods all resulted in significantly different oven moisture values. All laboratories results were within ± 3 standard deviations of the mean for each sample. The AOAC ranking test for laboratories , however, did identify 2 laboratories as outliers. Removing these 2 laboratories from the data pool did not change the outcome of the statistical analysis for 5 of the 6 samples. For one of the grass hay samples, trimming the outlying laboratory eliminated the significant effect of laboratories on oven moisture results. In every case, the current NFTA method (135° C for 2 h) produced significantly higher moisture than the other methods. Little difference was observed in reproducibility among the various methods. Comparison to Karl Fischer moisture technique-Paired t-tests comparing each oven method to The Karl Fischer technique were conducted. There was no significant difference (at the 0.01 level) between 105° C for 3 h and Karl Fischer values for the materials studied. Both the 105° C for 6 h and 135° C for 2 h methods resulted in significantly higher moisture results than The Karl Fischer method using homogenization extraction. Conclusions-Based upon agreement with the Karl Fischer technique, the 105° C for 3 h oven method best represents the true moisture content of alfalfa and grass hays. Even for corn silage, this method appears better than other oven methods currently available. The NFTA will adopt this method as the reference method for moisture, and will coordinate an AOAC collabo-rative study on the 105° C for 3 h method. SPE/LC Method for Determining Vitamin A in Feed-New Method Large variances are observed in the results of analysis of vitamin A in the AAFCO Feed Check Sample Program. Poor performance of vitamin A methods is due to many problems, some of which occur during the extraction of vitamin A from the hydrolysate, and subsequent evaporation of hexane. Problems that occur at this step include degradation of retinol upon exposure to heat and light, problems associated with certain lots of hexane, and incomplete extraction. SDB-XC Poly(styrenedivinylbenzene) extraction disks have been used successfully to quantitatively extract retinol from the hydrolysis mixture. Vitamin A was determined on 20 samples by both the AOAC 974.29 colorimetric method and by the SPE/LC method. Vitamin A concentrations obtained by SPE/LC ranged from 81 to 125%, and averaged 102% of those obtained by AOAC 974.29. Five 10 g portions of soybean meal blank material were spiked with vitamin A acetate standard solutions (0.109, 0.547, 1.09, 11.02, 110.2 IU vitamin A acetate), and recoveries were 94, 94, 93, 101, and 97%, respectively. Five samples of feed containing vitamin A were spiked with vitamin A acetate standard solution, and recoveries from 87 to 100% were obtained. The use of solid-phase extraction (SPE) disks can facilitate the extraction process, reduce labor input, improve recoveries, and eliminate the use of hexane and the evaporation step. Detection limits for the SPE disks can be as low as 100 IU/lb, depending on the volume of hydrolysate applied to the disk and the volume of methanol used to elute the vitamin A. An AOAC collaborative study on the method is planned. AOAC Official Method 942.05, Ash of Animal Feed-Existing Method Problems with AOAC Official Method 942.05, Ash of Animal Feed, have been reported by the pet food industry; 2 h at 600° C is not always sufficient for carbon-free ash of feed materials , such as corn gluten meal. The problems reported have been reproduced in the GR's laboratory. The Corn Refiners Association confirmed that 2 h is not a sufficient ash time for corn gluten meal. Materials other than corn gluten meal have been reported as problematic.