Digestibility of dry matter, nitrogen and minerals in biosolids

Abstract

Digestibility of dry matter (DM), nitrogen (N) and minerals in food processing 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 (74%) and D (72%) than for Diets S (83%) and M (79%). Effects of diets upon digestibilities of fiber and N were similar to effects upon DM digestibility. Digestibilities of minerals were not different among diets. The in situ digestibility of DM in BS was about 50%, compared to about 70% and 90% for alfalfa and soybean meal, respectively. In Experiment 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 Diets U (62%), S (64%) and D (64%) was greater than for Diet W (54%). Digestibility 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 digestibility of N in BS resulted in low ruminal ammonia, which reduced ruminal DM and energy digestibility and decreased volatile fatty acid 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 increase the digestibility of DM and N in BS.