Tryptophan Bioavailability in Soybean Meal for Young Pigs

Purdue University 1998 Swine Research Report. Several studies have been conducted to determine the bioavailability of amino acids for young pigs in the 22 to 45 lb live weight range (Sato et al., 1987; Kovar et al., 1993; Adeola et al., 1994). Bioavailability assays based on animal performance provide relative information on the capacity of a feed ingredient to provide a specific limiting amino acid for maintenance and growth. Commonly used dependent variables in a slope-ratio assay are weight gains (non-partitioned or partitioned) and gain:feed ratio. Although the independent variable used may be influenced by the choice of dependent variable, amino acid intake has been preferred by most investigators. There is evidence that bioavailability estimates vary depending on the choice of independent variable, but this has not been systematically investigated. An obvious question would be, to what extent do the dependent and independent variables affect the estimates of bioavailability? To evaluate this, the bioavailability of tryptophan in soybean meal was estimated by the slope-ratio assay using supplemental level, daily total intake, and daily supplemental intake of tryptophan as independent variables.