Estimation of relative bioavailability of nutrients using SAS procedures.

Abstract

The General Linear Models procedure (PROC GLM) in SAS/STAT software can be programmed to perform the standard statistical analyses used for relative bioavailability studies. The first steps are validity checks to test for statistical validity (linearity), fundamental validity (intersection of regression lines at 0 supplemental level), and equality of the basal diet mean to the point of intersection. The CLASS variable capabilities of PROC GLM can be exploited to expedite these tests. After the validity checks, the GLM procedure can be used to obtain parameter estimates for calculation of relative bioavailability. Optional output provides an inverse matrix to calculate standard errors of slopes and slope ratios. Logarithmic and other transformations of the dependent variable to reduce variance heterogeneity or achieve linearity for subsequent calculation of appropriate bioavailability values also can be accomplished within the SAS System. When nonlinear regression models are more appropriate than linear models, the NLIN procedure can be used.

Bioavailability of methionine hydroxy analog-calcium salt relative to dl-methionine to support nitrogen retention and growth in starter pigs

“…The slope-ratio assay has long been used to determine the RBV of nutrients in animals (Littell et al, 1997). In the current study, the slope-ratio assay estimated the RBV of MHA-Ca to DL-Met using N retention expressed as % of intake as a response criterion to be 71% on product-to-product basis.…”

“…Orthogonal-polynomial contrasts were used to determine linear and quadratic effects of increasing levels of DL-Met and MHA-Ca on response criteria, and the effect of Met sources. N retention data were subjected to multiple linear regression analyses to verify the fundamental validity assumptions of the slope-ratio assay (Littell et al, 1997), which include testing for linearity of responses, equality of the intercept and equality of the common intercept to the mean of the basal diet. The statistical validity tests described by Littell et al (1997) determine whether the average of the two slopes is different from zero and if the slopes of the individual lines are different from each other.…”

“…N retention data were subjected to multiple linear regression analyses to verify the fundamental validity assumptions of the slope-ratio assay (Littell et al, 1997), which include testing for linearity of responses, equality of the intercept and equality of the common intercept to the mean of the basal diet. The statistical validity tests described by Littell et al (1997) determine whether the average of the two slopes is different from zero and if the slopes of the individual lines are different from each other. Because the requirements for fundamental validity were met, the multiple linear regression analysis was performed using the following equation:…”

“…The RBV of MHA-Ca as compared with DL-Met was calculated as the ratio of their linear slopes (i.e. c/b 3 100) as described by Littell et al (1997).…”

“…Like MHA-FA, the re-introduction of MHA-Ca has generated questions about its relative bioavailability (RBV) compared with DL-Met as a Met source (Elwert et al, 2008). In animal nutrition, the term 'bioavailability' refers to the degree to which an ingested nutrient in a particular source is absorbed -E-mail: martin_nyachoti@umanitoba.ca in a form that is utilized for metabolic purposes by the animal (Littell et al, 1997). It is important to determine the RBV of these Met sources to facilitate efficient diet formulation and animal production, and to minimize nutrient excretion.…”