Variability among sources and laboratories in analyses of wheat middlings

A cooperative research study was conducted by members of a regional committ ee (North Central Regional Committee on Swine Nutrition [NCR-42]) to assess the variability in nutrient composition (DM, CP, Ca, P, Se, NDF, and amino acids) of 14 sources of wheat middlings from 13 states (mostly in the Midw est). A second objective was to assess the analytical variability in nutrie nt assays among 20 laboratories (labs; 14 experiment station labs and six c ommercial labs). Wheat middlings were obtained from each participating stat ion's feed mill. The bulk density of the middlings ranged from 289 to 365 g /L. The number of labs that analyzed samples were as follows: DM and CP, 20 ; Ca, 16; P, 15; Se, 7; NDF, 10; and amino acids, 9. Each lab used its own analytical procedures. The middlings averaged 89.6% DM, 16.2% CP, .12% Ca, .97% P. 36.9% NDF, .53 mg/kg Se, .66% lysine, .19% tryptophan, .54% threoni ne, .25% methionine, .34% cystine, .50% isoleucine, and .73% valine. As exp ected, there was considerable variation in nutrient composition among the 1 4 sources (P < .01), especially for Ca (.08 to .30%) and Se (.05 to 1.07 mg /kg). "Heavy" middlings (high bulk density, greater than or equal to 335 g/ L), having a greater proportion of flour attached to the bran, were lower i n CP, lysine, P, and NDF than "light" middlings (less than or equal to 310 g/L), having cleaner bran, resulting in negative correlations between bulk density and CP (r = -.61), lysine (r = -.59), P (r = -.54), and NDF (r = -. 81). Each 1-percentage-point increase in CP in the wheat middlings was asso ciated with .0235 (r(2) = .61) and 2.1 (r(2) = .39)-percentage-point increa ses in lysine and NDF, respectively. Lysine content was associated with NDF , CP, and bulk density of wheat middlings (r(2) = .88). There was considera ble variation among laboratories (P < .01) in analysis of all nutrients. Th e CV among sources (100.sigma(S)/mean) was greater than among labs (100.sig ma(L) /mean) for CP, Ca, P, Se, and NDF, but the CV among labs was greater than that among sources for DM and all of the amino acids except lysine and phenylalanine.