The North Central Research-42 Committee on Swine Nutrition conducted a study to compare the variability in nutrient composition of corn and soybean meal from 16 sources and to assess the analytical variability of 22 laboratories. Each laboratory used their own analytical procedures. The samples of corn and soybean meal varied in their composition depending on the area of origin. The greatest variation was seen in selenium concentration in both corn and soybean meal. The selenium content of the soybean meals ranged from 0.08 to 0.95 mg/kg. The crude protein and lysine in soybean meal was positively correlated with a regression coefficient of r2=0.81. Lysine in soybean meal increased by 0.063 percentage points for each one percentage point increase in protein. With the exception of crude protein and selenium, the analytical variability among laboratories was as great as, and in some cases greater than, the variability in nutrient composition among the sources of corn and soybean meal.
The take-home messages are 1) variation in laboratory analyses of certain nutrients, especially amino acids, may be as great as, or even greater than, the variability of nutrient composition of corn and soybean meal from different geographical areas of the United States, 2) selenium values are highly variable, and 3) lysine can be fairly accurately predicted from the crude protein content of soybean meal.
Cromwell, G.L. and co-workers. 1999. Variability among sources and laboratories in nutrient analyses of corn and soybean meal. J. Animal Sci. 77:3262-3273.