Dried, irradiated sewage solids as supplemental feed for cattle

Sewage solids were collected as primary settled solids and then dried and gamma-irradiated (using /sup 60/Co or /sup 137/Cs) to absorbed dosage of about one megarad to minimize viable parasites and pathogenic organisms. Nutrient composition and bioassays with rumen microbes suggested prospective usage as supplemental feed for ruminants. Short-term experiments with sheep and then with cattle further suggested that usage of nutrients could be beneficial and that accumulation of heavy metals was not excessive. A longer-term feeding trial with cattle fed sewage solids as 20% of diet for 68 days demonstrated that tissue uptake of elements such as Cu, Fe and Pb was measurably increased, but not sufficient to exceed ranges considered normal. Likewise, of 22 refractory organic compounds having toxicological interest, only a few were detectible in adipose tissue and none of these exceeded levels that have been reported in tissues from cattle produced conventionally. In a large-scale experiment, beef cows grazing poor-quality rangeland forage during late gestation-early lactation were given either no spplemental feed or cottonseed meal or experimental supplement comprised of 62% sewage solids. Supplements were provided for 13 weeks until rangeland forage quality improved seasonably. Supplemental cottonseed meal for cows improved weaning weights of calves bymore » about 11% over unsupplemented controls; whereas, supplement with 62% sewage solids improved calf weaning weights by about 7%. Hazards or risks to animals or to human health appear to be slight when sewage solids of this type are fed as supplemental feeds to cattle in production programs of this type.« less