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Effects of Long-Term Consumption of Sewage Solids on Blood, Milk and Tissue Elemental Composition of Breeding Ewes¹

New Mexico State University³, Las Cruces 88003

Abstract

Fine-wool ewes received for 2 yr a complete pelleted basal diet (11% protein) or the basal diet fortified with 3.5% cottonseed meal (CSM; 12% protein) or gamma-irradiated (1 megarad) dried solids (SS; 12% protein) from primary (undigested) sewage (Las Cruces, New Mexico, municipal sewage). Five ewes fed each diet were sampled to determine Ag, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, P, Pb and Zn in blood, milk and tissues. Tissues and blood were sampled at slaughter 40 d after weaning of lambs. Mean whole blood mineral concentrations were similar (P>.05) among treatments 3 d postpartum; however, at 42 d after lambing (mean ± SE) both basal- (54 ± 2 µg/ml) and sewage-fed (54 ± 2 µg/ml) ewes had elevated (P<.05) blood Ca compared with ewes fed CSM (46 ± 2 µg/ml). No biologically important differences were detected in the concentrations of elements in milk. Ewes fed SS had lower (P<.05) blood Fe than animals in the other groups. Sewage-fed ewes also had higher (P<.05) liver Fe (1,092 ± 100 µg/g) than basal-fed ewes (626 ± 100 µg/g); whereas Fe in CSM-fed ewes (873 ± 100 µg/g) was similar to both. Basal-fed animals had 1.1- to 1.3 times more (P<.05) liver Mg and two- to threefold higher liver Na than CSM or SS. Livers from SS-fed ewes had higher concentrations (P<.05) of Cd (1.5- to 1.6-times) and Pb (1.4- to 1.9-times) than livers from CSM- or basal-fed ewes. Cadmium was 1.2- to 1.5-times higher (P<.05) in kidneys from ewes receiving the sewage product, but all values were less than 1 µg/g. Lead was not detectably increased in kidney samples. Spleen Ca, Fe and Ni and muscle Ca were increased due to feeding SS; however, no elements in bone samples from SS-fed animals were elevated above the control groups. Consumption of a diet containing 7% SS throughout a 2-yr period had only minor effects on element contents of blood, milk or tissues.

¹ Journal Article 1035 of the New Mexico Agr. Exp. Sta. This study was supported in part by Contract No. DE-ACO4-76ET-33626, U.S. Dept. of Energy, 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, B. J. Gardner, S. A. Mischler, C. W. Crusberg, S. Bustos and M. Neave is acknowledged. Direct reprint requests to G. S. Smith.