Nitrogen, Energy, and Weight Losses Associated with Drying and Grinding of Poultry Feed and Excreta

Abstract

Three experiments were conducted to determine nitrogen, energy, and dry matter loss associated with the drying and grinding of poultry feed and excreta. Freeze-dried and 60 C oven dried excreta samples incurred similar weight losses; however, weight losses increased linearly when excreta samples were oven dried at 60, 100, or 120 C. Substantial sample losses (3.5 to 5.2%) due to grinding were observed. No nitrogen or energy losses from drying were detected from analyses of fresh and dried excreta.In the second experiment, feed (150 g) and excreta (150 g), which had been dried at 40 C and equilibrated with atmospheric moisture, were ground and stored in screw cap containers. One-gram subsamples were dried at 40, 60, 80, 100, 120, 140, or 175 C for 24 hr. Residual weight decreased with increasing drying temperature. When expressed per gram of original sample, the energy content of feed and excreta samples remained unchanged by drying at 100 C or less but decreased significantly at higher temperatures. Nitrogen composition of feed and excreta samples exhibited a similar trend, except loss of excreta nitrogen (2% of the total) was significant at 100 C.In the final experiment, feed and excreta samples from the previous experiment were oven dried for 24 hr, extracted with N,N-dimethylformamide, and titrated with Karl Fischer reagent. Feed samples retained 5.5, 3.0, and .6% water, and excreta samples retained 5.9, 3.2, and .5% water when oven dried for 24 hr at 40, 60, or 80 C, respectively. When dried at 100, 120, or 140 C, decompositional losses amounted to .3, 1.5, and 2.3% for feed and 1.4, 2.8, and 4.5% for excreta, respectively. A drying temperature of 90 C was deemed to be the most satisfactory to remove water and yet prevent decomposition of feed and excreta samples.