Effects of dietary substitution with raw and heat-treated cowpea (Vigna unguiculata) on intestinal transport and pancreatic enzymes in the pig

Tropical grain legumes represent potentially important feed for farm animal s. However, diarrhoea and poor growth performance have been reported, due t o the various anti-nutritional factors they contain. This study addressed i n particular whether dietary cowpea impaired the growth of pigs, whether th e small intestinal Na+/D-glucose coabsorptive transport capacity was decrea sed, whether the Cl- secretory capacity was increased, and, finally, whethe r these parameters were affected by heal treatment of cowpea. Pigs, 4 weeks old, were fed for 3 weeks with one of three diets: (i) standa rd soy, (ii) 75 % of soy substituted with raw cowpea, or (iii) 75 % of sop substituted with heat-treated cowpea. The absorptive and secretory capaciti es of the jejunum and ileum were measured with the Ussing chamber technique . Weight gain, feed intake, pancreatic protein and enzyme concentrations an d levels of the blood hormones glucagon and cholecystokinin were also measu red. The Na+ transport capacity was measured as the increase in short-circuit cu rrent (I-SC) when D-glucose was added to the luminal side in the Ussing cha mbers. I-SC was significantly higher in the jejunum from raw cowpea-fed pig s than in the jejunum from standard soy-fed pigs, with no difference betwee n the tare cowpea-fed groups. The phosphodiesterase inhibitor theophylline was subsequently added bilaterally, and the increase in I-SC indicated the cAMP-dependent Cl- secretory capacity. In the jejunum this was significantl y higher in raw and heat-treated cowpea-fed pigs than in standard soy-fed p igs. In contrast, there were no differences in the ileal transport capaciti es. There were no differences in the pancreatic protein and trypsin concent rations or the blood hormones, but the raw compea-fed pigs had significantl y lower pancreatic amylase than standard sop-fed pigs. Weight gain and feed intake were lowest in the cowpea-fed groups, with no significant differenc e between the two groups. In conclusion, the hypothesis of impaired small intestinal absorption of D- glucose and Na+ as causing malabsorption, and therefore impaired growth, du ring cowpea substitution in the feed may be firmly rejected. The increased Cl- secretory capacity, although moderate, may contribute to the higher inc idence of post-weaning diarrhoea in cowpea-fed pig, as observed in other st udies. Additionally, the decreased food intake, feed conversion and weight gain were unaffected by heat treatment, further suggestion involvement of h eat-stable anti-nutritional factors.