A comparative evaluation of ileo‐rectal anastomosis techniques for the measurement of apparent precaecal digestibilities of folate, niacin and pantothenic acid

Abstract

Introduction There is a great need for better understanding of the intestinal bioavailability of B‐vitamins and the factors that influence it. In food products, however, nutrient content does not necessarily imply the proportion of nutrient content actually absorbed. Thus a variety of experimental approaches have been used for determining the intestinal bioavailability of food vitamins. They include measuring changes in tissue vitamin levels, urinary vitamin excretion and growth in response to known intakes of vitamin‐containing foods (e.g. Southern and Baker 1981; Gregory and Litherland 1986; Abad and Gregory 1987; Clifford et al. 1990; Swatilo et al. 1990; Yu and Kies 1993; Matte and Girard 1994). Potential limitations of those animal bioassays centre mainly on the role of the intestinal microflora and the extent of enhancement or inhibition of their vitamin synthesis by dietary components. The endogenous vitamin synthesis by the intestinal flora, with possible uptake in the distal part of the small and/or large intestine, is a complicating factor for nearly all B‐vitamins. The components of test diets that would stimulate the synthesis of B‐vitamins by intestinal microorganisms could therefore cause overestimation of dietary vitamin availability in conventional bioassays. Application of in‐vitro assays has also been reported for water‐soluble vitamins, but these are not recommended because of the limitations in extrapolation of the results to the situation in vivo (Holler et al. 1975; Seyoum and Selhub 1998). In principle, methods using stable isotopes will give the most reliable information concerning intestinal absorption, but their application is still limited, mainly because stable isotopes are not commercially available and specialized facilities and expertise are required. Ileo‐rectal anastomosis has been proposed as an alternative method for calculating the intestinal availability of nutrients (Herrmann et al. 1988; Green and Kiener 1989; Laplace et al. 1989; Hennig et al. 1990; Roth‐Maier et al. 1998). The most important advantage of ileo‐rectal anastomosis for measuring vitamin digestibility is the prevention of vitamin synthesis by the intestinal microflora and coprophagy, because the digesta can be collected quantitatively via the anus. In this respect two different techniques of ileo‐rectal anastomosis have been developed for pigs: the end‐to‐side (ESV) and end‐to‐end (EEV) ileo‐rectal anastomosis with preserved ileo‐caeco‐colic valve. Both methods have already been compared for their use as digestibility assays for the vitamins including thiamin, riboflavin and vitamin B6 (Roth‐Maier et al. 1998). The objective of the present study was to compare both the ESV and EEV techniques with regard to the digestibility values of folate, niacin and pantothenic acid, which has not been tested hitherto. In addition, in order to examine age‐ or time‐related effects on vitamin digestibility two different experimental periods after surgery were chosen for measurement.