Two experiments were conducted to investigate the effects of increasing concentrations of supplemental purified
soybean agglutinin on performance, apparent
nitrogen digestibility, plasma
insulin and cholecystokinine (CCK) levels in rats as well as on the growth of the small intestine and pancreas. In Experiment 1, a 10-day
nitrogen balance trial was conducted with 24 male Sprague-Dawley rats (mean BW 85 g) that were randomly allotted to one of four dietary treatments. Rats in each group were provided daily with 7 g of a
casein-
cornstarch based diet (control) or a diet supplemented with purified
soybean agglutinin at 0.4, 0.6 or 0.8 mg/g. Urine and faeces were collected daily and stored at -20 degrees C until analysis. In Experiment 2, 30 male Sprague-Dawley rats (mean BW 75 g) were divided into five groups for a 20-day growth experiment. Each rat was fed daily 7 g of a
casein-
cornstarch based diet (control) or a diet supplemented with purified
soybean agglutinin at 0.4, 0.8, 1.2 or 2.0 mg/g. All experimental diets were adjusted to contain a similar level of nutrients. Results from the two experiments showed that supplementation of
soybean agglutinin below 2.0 mg/g diet had no significant effect on rat performance. However, rats receiving 2.0 mg
soybean agglutinin per gram of diet showed a significant reduction in
weight gain compared to the control group. Incorporation of
soybean agglutinin in the diet reduced apparent
nitrogen digestibility and the retention of dietary
nitrogen by increasing
nitrogen loss from the faeces and urine. In addition, plasma CCK level increased with increasing inclusion of
soybean agglutinin in the diet. On the contrary, the plasma
insulin level declined as
soybean agglutinin level increased.
Soybean agglutinin induced a
polyamine-dependent hyperplastic and hypertrophic growth of the small intestine and pancreas by increasing the contents of
protein,
RNA and
DNA, though the increase in weight of small intestine was not significant. Furthermore, 1.2 and 2.0 mg
soybean agglutinin per gram of diet promoted proliferation of the jejunum mucosa, while the structure of the brush border epithelium of small intestinal had no damaging change and no diarrhoea was observed in any treatment group. Based on these results, supplementation of low doses of
soybean agglutinin or
soy protein to parenterally-fed animals affected by atrophic small intestine may promote small intestinal growth.