DIGESTIBILITY OF DRY-MATTER, NITROGEN AND MINERALS IN BIOSOLIDS

Digestibility of dry matter (DM), nitrogen (N) and minerals in food pr ocessing biosolids (BS) was determined. In Experiment 1, three diets ( 9% protein) were formulated from corn silage, ground corn, starch, and either dried BS (D), soybean meal (S) or soybean meal plus additional Ca and P (M). These diets plus a control (C, 6% protein) were fed to fistulated cows, Apparent digestibility of DM was lower for Diets C (7 4%) and D (72%) than for Diets S (83%) and M (79%). Effects of diets u pon digestibilities of fiber and N were similar to effects upon DM dig estibility. Digestibilities of minerals were not different among diets . The in situ digestibility of DM in BS was about 50%, compared to abo ut 70% and 90% for alfalfa and soybean meal, respectively. In Experime nt 2, chopped corn forage was ensiled with urea (U), soybean meal (S), dried BS (D) or wet BS (W) and fed to sheep. DM digestibility of Diet s U (62%), S (64%) and D (64%) was greater than for Diet W (54%). Dige stibility of N in Diet D (48%) was lower than in Diets S (52%) and U ( 54%); digestibility of N in Diet W (42%) was lower than in Diet D. Low digestiblity of N in BS resulted in low ruminal ammonia, which reduce d ruminal DM and energy digestibility and decreased volatile fatty aci d concentrations. Dried BS were more digestible than native (wet) BS; BS could be added to silage as means of feeding and probably are best suited for maintenance diets. Bioprocessing methods are needed to incr ease the digestibility of DM and N in BS.