The growth of an animal depends in part on its capacity to digest and assimilate ingested macromolecules, and any impairment of this is expected to constrain growth. The objective of this study was to investigate the development of small intestinal size and digestive capacity of the jejunum in growing pigs. The weight, lenght, surface area, and mucosa weight of the small intestine were measured when pigs are 1, 3, 5, and 9 wk of age. Sucrase and alkaline phosphatase (ALP) activities of the jejunal brush-border membrane, prepared by differential centrifugation and Mg2+ precipitation, were determined at the respective postnatal stages. Body weight increases 7-fold from 2,7 kg at 1wk to 23.32 kg at 9 wk postnatal. Body weight gains were greater (P <0.05) from wk 3 to 5  than from wk 1 to 3. Weights of the small intestine and of the intestinal mucosa increased faster (P <0.05) from 3 to 5 wk than from 1 to 3 wk; the siowest increase occurred from 5 to 9 wk. Weights of the duodenum, jejunum, and ileum, and mucosa from the respective sections incerased (P < 0.05) as pigs grew from 3 to 9 wk.

Mucosa weight relative to the weight of the section was greater (P < 0.05) for the duodenum and jejunum than for the ileum at 9 wk of age. Between the ages of 3 and 9 wk, the increase in mucosa weight was highest for the jejunum followed by the duodenum and the ileum. The increase was greatest for the duodenum followed by the jejunum and the ileum when mucosal weight was expressed per unit of appropriate intestinal section weight (table 1).

 

 

There was a 55-fold increase in jejunal sucrase activity from 1 to 9 wk; the greatest rate of increase occurred between 5 and 9 wk. Total jejunal ALP activities in pigs at 9 wk was greater (P < 0.05) than at 5 wk, wich in turn was greater than at 1 wk of age (table 2).