Ileal and faecal protein digestibility measurement in humans and other non-ruminants – a comparative species view

 

Wouter H. Hendriks, Ju¨rgen van Baal and Guido Bosch 

 

1 Animal Nutrition Group, Wageningen University, PO Box 338, 6700 AH Wageningen, The Netherlands

2 Faculty of Veterinary Medicine, Utrecht University, PO Box 80.151, 3508 TD Utrecht, The Netherlands

(Submitted 29 April 2011 – Final revision received 29 July 2011 – Accepted 6 October 2011)

 

Abstract

A comparative non-ruminant species view of the contribution of the large intestinal metabolism to inaccuracies in nitrogen and amino acid absorption measurements is provided to assess potential implications for the determination of crude protein/amino acid digestibility in adult humans consuming lower digestible protein sources. Most of the amino acids in the hindgut are constituents of the microorganisms and significant microbial metabolism of dietary and endogenous amino acids occurs. Bacterial metabolism of nitrogen-containing compounds leads to a significant disappearance of nitrogen in the large intestine. Literature data show that some 79 % of the nitrogen entering the large intestine of the horse is absorbed. For dogs, sows, and growing pigs these estimates are 49, 34 and 16 %, respectively. The coefficient of gut differentiation of humans compares closely to that of dogs while the coefficient of fermentation in humans is the lowest of all non-ruminant species and closest to that of cats and dogs. Large intestinal digesta transit times of humans compare closest to adult dogs. Significant amino acid metabolism has been shown to occur in the large intestine of the adult dog. Use of the growing pig as an animal model is likely to underestimate the fermentation of amino acids in the human large intestine. Based on the significant degree of fermentation of nitrogen-containing components in the large intestine of several non-ruminant species, it can be expected that determination of amino acid digestibility at a faecal level in humans consuming low quality proteins would not provide accurate estimates of the amino acids absorbed by the intestine.

 

Key words: protein: large intestine: fermentation: non-ruminant: review

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The coefficient of gut differentiation (area large intestine/area small intestine £ 100), an indicator of the importance of the functional participation of the large intestine in the absorptive process(68), shows values for humans of 7, cats 9, dogs 11, rats 30, mice 31, pigs 41, horses 51, guinea pigs 72, and rabbits 103. Similarly, the coefficient of fermentation (large intestinal/small intestinal volume £ 10), an indicator of the participation of the large intestine in the fermentation processes, is for humans only 0·7, cats 2·9, dog 4·1, rats 10·2, mice 7·2, pigs 9·9, horses 29·8, guinea pigs 31·7, and rabbits 71·2. These data indicate that the large intestine of the dog would be the closest match to humans when it comes to large intestinal morphology