Pancreatic insulin concentrations are influenced by the composition of the diet but the mechanism responsible for the change is not always clear. Possible mechanisms were investigated in this work by feeding maize or lucerne pellets to lambs and examining the effect on blood metabolites, glucose tolerance, and pancreatic insulin concentrations. Feeding maize pellets significantly increased blood glucose (54.1 v. 46.9 mg01o), plasma insulin (27.3 v. 16.3 flU/ml), pancreatic insulin (435 v. 235 IU/lOO g pancreas), and glucose clearance (T~= 20.5 v. 25.3 min) compared to lucerne pellets. There were no significant differences in the molar percentages of blood propionate or concentrations of blood urea. It is concluded that starch escaping rumen fermentation in lambs fed maize increases blood glucose concentrations which stimulates the pancreatic secretion of insulin; the latter is responsible for the elevation in plasma and pancreatic insulin concentrations.
Eighteen-week-old lambs were fed lucerne or maize indoors, or grazed lucerne or rape outdoors. After a lO-week feeding period, the animals were sacrificed and the pancreatic insulin concentrations determined. The effects of the dietary treatments were compared with a control group of lambs slaughtered at 18 weeks and commercially produced lambs which had been grazing lucerne or pasture. At 18 weeks, the control lambs had pancreatic insulin concentrations of 341 ± 7 IV insulin/100 g pancreas. Grazing lucerne for a further 12 weeks significantly (P< 0.01) reduced the insulin concentrations to 267 ± 10 IV insulin/ 100 g pancreas, whereas feeding pelleted maize or grazing rape significantly (P
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