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Effects of Dietary Sewage Solids on Feedlot Performance, Carcass Characteristics, Serum Constituents and Tissue Elements of Growing Lambs¹

New Mexico State University³, Las Cruces 88003

Abstract

Twenty fine-wool wether lambs were allotted randomly at weaning to be fed a conventional diet (CD) formulated for growing lambs, or the same basal mixture plus dried gamma-irradiated solids from primary sewage sludge (SS) incorporated as 7% of the dry matter. Feedlot performance and chemical elements in whole blood were monitored during 90 d, after which lambs were slaughtered and carcass data were collected. Concentrations of Ag, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, P, Pb and Zn were measured in livers, kidneys, bones, spleens and muscles. Sewage solids in the diet did not affect performance appreciably, although dressing percentages from lambs fed SS were 4% lower than CD-fed animals (P<.05). Rib eye areas, fat thicknesses, quality and yield grades were similar (P>.05). Element concentrations in whole blood at weaning, after 56 d of the feeding trial and at slaughter did not differ (P<.05) between dietary groups. Serum chemistry determinations showed no biologically meaningful patterns related to diets. Lambs fed SS had higher (P<.05) concentrations of Cu in livers (51.1 vs 34.3 ± 3.8 µg/g, mean ± SE) and Pb in kidneys (4.0 vs 2.2 ± .3 µg/g) and lower (P<.05) Mg in kidneys (.69 vs .72 ± .01 mg/g). None of the elements in spleen and muscle tissue differed (P>.05) between diet groups. Lambs fed SS had elevated (P<.05) bone Co, Cu, Fe, K and Na compared with those of CD. Lead concentrations in bone were increased (P<.05) by SS over CD (30.5 vs 26.3 ± .8 µg/g), but Cd and Zn did not differ (P>.05). A feedlot diet with 7% SS did not appear to adversely affect growth or carcass characteristics of lambs. Serum clinical profiles and chemical elements in blood and tissues were affected negligibly by SS as 7% of the diet.

¹ Journal Article 1036 of the New Mexico Agr. Exp. Sta. This study was supported in part by U.S. Dept. of Energy, Albuquerque under Contract No. DE-AC04-76ET-33626 and was conducted in cooperation with Sandia National Laboratories, Albuquerque, NM.

² Present address: Univ. of Florida Agr. Res. Center, Ona 33865.

³ Dept. of Anim. and Range Sci. Technical assistance by D. G. Morrical, R. E. Hudgens, M. O. Vanderwart, L. A. Tierney, J. D. Thomas, B. J. Gardner, S. A. Mischler, C. W. Crusberg, S. Bustos and M. Neave is acknowledged. Direct reprint requests to G. S. Smith.