Comparative sulfur analysis using thermal combustion or inductively coupled plasma methodology and mineral composition of common livestock feedstuffs

¹ USDA-ARS, Ames, IA 50011
² University of Minnesota, St. Paul, MN 55108

^* To whom correspondence should be addressed. E-mail: brian.kerr{at}ars.usda.gov.

	Abstract

The objective of this study was to compare the use of thermal combustion (CNS) and inductively coupled plasma (ICP) to measure the total sulfur (S) content in plant-, animal-, and mineral-based feedstuffs, and to provide concentrations of other macro- and micro-minerals contained in these feedstuffs. Forty five feedstuffs (464 total samples) were obtained from suppliers as well as swine feed and pet food manufactures throughout the U.S. Mineral data from IPC analysis were summarized on a DM basis using sample mean and SD while the comparison of total S content between CNS and ICP was examined by bivariate plot and correspondence correlation. Analyses of a wide range of feedstuffs by CNS and ICP for total S were comparable for all but a few feedstuffs. For potassium iodide and tribasic copper chloride, ICP estimated total S to be lower than when analyzed by CNS (bias = 2.51 ± 0.15 SE, P < 0.01). In contrast, for defluorinated phosphate and limestone, ICP estimated total S to be greater than when analyzed by CNS (bias = -1.46 ± 0.51 SE, P < 0.01). All other samples had similar estimates of total S, whether analyzed by CNS or ICP. As expected, S composition varied greatly among feedstuffs. For total S, plant-based feedstuffs generally had lower total S compared to animal-based feedstuffs, and minerals supplied in sulfate form had the greatest concentration of total S. In addition to total S, mineral composition data are provided for all feedstuffs as obtained by ICP analysis. Within specific feedstuffs, mineral composition was quite variable, potentially due to low concentrations in the feedstuff causing high mathematical variation or due to the source of feedstock obtained. In general, analyzed values of P were similar to previous tabular values (NRC, 1988). These data provide feed formulators a database from which modifications in dietary minerals can be accomplished from which mineral requirements can be met more precisely in order to reduce losses of minerals into the environment.

Key Words: analysis, feedstuffs, inductively coupled plasma, dietary sulfur, thermal combustion