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

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. S outhern and B aker 1981; G regory and L itherland 1986; A bad and G regory 1987; C lifford et al. 1990; S watilo et al. 1990; Y u and K ies 1993; M atte and G irard 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 (H oller et al. 1975; S eyoum and S elhub 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 (H errmann et al. 1988; G reen and K iener 1989; L aplace et al. 1989; H ennig et al. 1990; R oth-M aier 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 (R oth-M aier 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.