Effects of dietary protein and sunflower seed supplementation on physico-chemical characteristics of small intestinal digesta and plasma cholecystokinin concentrations in lambs

Two experiments in a 2 x 2 factorial design were conducted with weaned lambs to determine the effects of supplementing either high forage (Experiment 1; 140 d) or grain (Experiment 2; 70 d) diets containing either 12 or 16% protein without or with sunflower seed (SS) supplement (14% of diet dry matter DM) on plasma cholecystokinin (CCK) concentration, and on absolute viscosity, protein, starch and fat content, and amylase activity in digesta collected from different parts of the small intestine. There were four treatment groups in each experiment with 11 or 12 lambs (five or six wethers and six ewes) per treatment group in Experiments 1 and 4, 8-lamb (ewes only) groups in Experiment 2. Each group was fed one of four experimental diets based on corn silage, corn grain and soybean meal in Experiment 1, and on barley grain, straw and soybean meal in Experiment 2. Soybean meal was used to achieve the appropriate concentration of dietary protein in both experiments, while straw was used in Experiment 2 to achieve equal dietary fiber in all diets. Concentrations of CCK were determined in jugular plasma obtained from each lamb (4 h after feeding) 6 weeks after the initiation of the experiment. After the end of the experiments all lambs were sacrificed and the digesta sampled within 15 min of slaughter from 50 cm sections of proximal, mid jejunal and distal small intestine. In Experiment 1, dietary SS increased (P < 0.05) plasma CCK concentrations of ewe lambs fed the high protein diet, but reduced (P < 0.05) digesta viscosity to 45.2 +/- 14.4 cP from 226.0 +/- 70.2 cP across all intestinal sections in all lambs fed the low protein diets. In lambs fed the low protein diet with SS, digesta fat content was increased across all sections. Digesta protein content was 61.9 +/- 8.22% in ewe lambs fed the high protein diet in proximal intestinal sections relative to 38.9 +/- 7.08% in lambs fed the low protein diet but neither dietary protein nor supplementation with SS had any effect on the amylase activity (micromolar reducing sugars released g(-1) DM min(-1)). In Experiment 2, dietary SS decreased (P < 0.05) viscosity of small intestinal digesta of lambs to 3.2 +/- 32.6 cP, in the distal regions of lambs fed the low protein diets relative to those receiving no SS (348 +/- 79.8 cP). Small intestinal digesta protein was higher (P < 0.05) in lambs fed high protein diets with SS and the amylase activity as micromolar reducing sugars released g(-1) DM min(-1) was increased (P < 0.05) in these animals as well. Dietary SS was effective in altering digesta viscosity and protein content in lambs irrespective of protein content of the diet, but the activity of the amylase was substantially increased by higher dietary protein in the barley grain based diets.