Morphometry of the intestine of the pig. II. Circumsection response to feeding schedules.

Weight measurement of the gastrointestinal organs (GIT) and morphometric measurements of circumsections of the small intestine (SI) have demonstrated profound responses to the level of dietary intake. The average response of pigs (all the same live body weight) gaining weight at a moderate rate (treatment LH) relative to pigs losing weight (HL) were as follows (+ denotes increase): GIT weight, +71.5%; SI weight, +84.8%; tissue fraction of SI mucosa, +16.0%; index of quantity of mucosa per SI circumsection, +64.7%; estimate of the mass of mucosa in the whole SI organ, +108%. Although the composition of circumsections from duodenum, jejunum, and ileum differed substantially and significantly, the effects of treatments were similar at each site. Of the 542-g response (LH vs HL) of the small intestine, estimates calculated from circumsection morphometry data indicate that 55 g, 11 g, and 476 g were from muscle, matrix, and mucosa, respectively. Changes in the size of the circumsection were much greater than changes in composition. The shift in the quantity of mucosa in the circumsection was about fourfold greater than would have been predicted from the tissue fraction of mucosa. The relationship between the morphometric responses and biochemical functions of the mucosa are important to understand digestive-absorptive capacities and nutrient requirements during and immediately after a major shift in food intake.