Small intestine of artificially reared rat pups: effect of caloric intake and dietary composition on growth and disaccharidase activities.

When rats were fed a cow milk formula (CMF) from 12 to 16 days of age at a caloric intake sufficient to support a body weight gain equal to mother-fed (MF) rats, their small intestine outweighed that of MF rats by 40%. If the caloric intake was reduced by approximately 40%, artificially reared (AR) rats exhibited intestinal weights similar to MF rats, but their body weight was lower than MF rats. Sucrase specific activity was precociously increased in all AR rats; this increase was higher in rats with low caloric intake than rats with high caloric intake. Conversely, lactase specific activity was significantly decreased in the ileum of all AR rats. As compared to MF rats, the total lactase activity was significantly lower only in rats with low caloric intake. When AR rats were fed a modified Ross Carbohydrate-Free formula (RCF) containing the same caloric density of protein, fat, and carbohydrate as rat milk, the intestinal growth and disaccharidase activities were the same as those of AR rats fed CMF. It is concluded that the weight gain of small intestine depends on the caloric intake of AR rats and both CMF and RCF are nutritionally equal in supporting intestinal growth. Changes in sucrase and lactase activities in AR rats appear to have no relation to compositional differences in CMF and RCF.