Quality of Meat from Cattle Fed Sewage Solids ¹

Beef heifers in a feedlot were fed an experimental (E) diet containing gamma-irradiated ("pasteurized") dried sewage solids as 20% of the diet. Similar heifers received a conventional diet and served as controls (C). Four heifers from each group were slaughtered at the 68th day of the feeding program. Carcasses from E were smaller than from C (202 versus 245 kg), had less fat thickness (.76 versus 1.0 cm) and less internal fat (2.5 versus 2.9%). Steaks, roasts and ground beef (composite of all trimmings) were displayed for 3 d in a refrigerated (2-4°C) meat case. Ground meat from E was superior to C in lean color and overall visual acceptance; but the reverse was true for steaks and roasts (P<.05). Steaks and roasts from C were evaluated slightly higher than E in firmness of lean, resulting from more subcutaneous carcass fat of C. Microbial contamination of carcasses was assayed by cultures from swabs taken from the diaphragm muscle and the 12/13th rib area of hanging sides (at slaughter and days 2 and 7 postmortem) and from swabs and core samples of product at day 0 and days 3 and 17 postmortem. Colony counts from core samples taken from bulk ground beef (C) and soaked in peptone water averaged 8.5 × 10⁴ for day 0 and 7.5 × 10⁶ for day 3 samples, while samples from E carcasses averaged 3.8 × 10⁴ (day 0) and 4.1 × 10⁷ (day 3). Colony counts from surface swabs of beef patties averaged 4.6 × 10⁴ (day 0) and 5. 7 × 10⁶ (day 3) for C and 6.5 × 10⁴ (day 0) and 9.4 × 10⁶ (day 3) for E. Microbial counts of the product surveyed in this study did not differ (P>.05) due to diets (E vs. C). Livers and kidneys from cattle fed the E diet had higher levels (P<.05) of Fe and Pb than those from cattle receiving the C diet.