Comparison of Oven-drying Methods for Determination of Moisture Content in Feed Ingredients

An accurate assessment of moisture content in feed ingredients is important because moisture influences the nutritional evaluation of feedstuffs. The objective of this study was to evaluate various methods for moisture content determination. In Exp. 1, the weight loss on drying (LOD) of corn, soybean meal (SBM), distillers dried grains with solubles (DDGS), whey permeate, whey powder, spray-dried porcine plasma (SDPP), fish meal, and a mixed diet of these 7 ingredients were measured by oven drying at 135°C for 2 h. Additionally, the samples were dried at 105°C for 3, 6, 9, 12, or 15 h. The LOD contents of the DDGS, whey permeate, and whey powder measured by drying at 135°C for 2 h were greater than the values measured by drying at 105°C for 3 h (p<0.05). All samples except SDPP (p = 0.70) dried at 105°C for 6, 9, 12, or 15 h caused more LOD compared with the samples dried for at 105°C for 3 h (p<0.05). The LOD contents of the individual ingredients were additive when dried at 105°C regardless of drying time. In Exp. 2, moisture contents of corn, SBM, wheat, whey permeate, whey powder, lactose, and 2 sources of DDGS (DDGS1 and DDGS2) were measured by the Karl Fischer method, oven drying at 135°C for 2 h, and oven drying at 125°C, 115°C, 105°C, or 95°C for increasing drying time from 1 to 24 h. Drying samples at 135°C for 2 h resulted in higher moisture content in whey permeate (7.5% vs 3.0%), whey powder (7.7% vs 3.8%), DDGS1 (11.4% vs 7.5%), and DDGS2 (13.1% vs 8.8%) compared with the Karl Fischer method (p<0.05). Whey permeate and whey powder were considerably darkened as the drying time increased. In conclusion, drying samples at 135°C for 2 h is not appropriate for determining the moisture content in whey permeate, whey powder, or DDGS as well as the mixed diet containing these ingredients. The oven-drying method at 105°C for 5 to 6 h appears to be appropriate for whey permeate and whey powder, and at 105°C for 2 to 3 h for DDGS.