Effects of increasing dietary grain on viscosity of duodenal digesta and plasma hormone, glucose and amino acid concentrations in steers

Effects of increasing the proportions of dietary barley grain or corn on viscosity of duodenal digesta supernatant and concentrations of cholecystokinin (CCK), glucose and amino acids in portal plasma and concentrations of CCK, insulin and glucose in jugular plasma were determined. Four steers (374 +/- 6.4 kg) were surgically fitted with ruminal and duodenal cannulae and indwelling portal vein catheters. The steers were fed diets containing 20, 40, 60, and 80% rolled barley or cracked corn (DM basis) replacing respective silages, in two experiments with 4 x 4 Latin square design. After adjusting the steers to the diets for 14 d, digesta samples from the duodenum and blood samples from the portal and jugular veins were collected twice daily for 5 d. Increasing the proportion of dietary barley or corn increased the viscosity [measured as centipoise (cP)] of duodenal supernatant (from 1.3 to 2.0 and from 1.5 to 2.8 cP, P < 0.05), respectively. Portal plasma CCK concentration increased linearly (2.4 to 4.9 pmol, P < 0.05) as the proportion of dietary barley increased. However, in corn-fed steers, the highest portal CCK concentrations were observed in steers receiving 20% corn and these concentrations were not affected by corn content of the diet. Increasing dietary barley resulted in a linear increase in jugular plasma CCK concentration of steers, but a linear (P < 0.05) decline was noted when corn was fed to steers in increasing proportions. Portal and jugular plasma glucose concentrations were not altered in barley-fed steers, but both portal and jugular glucose increased (P < 0.05) with increasing dietary corn. Jugular insulin concentration was higher in steers fed 80% barley or corn than in those receiving the diets with less grain. Total amino acid concentrations in portal plasma were higher by 30% in steers fed corn than in those fed barley, but were not affected by relative proportion of dietary corn. These data suggest that feeding cattle increasing proportions of barley or corn grain increases duodenal viscosity, which, together with components of digesta, may be involved in affecting the secretion of hormones, such as CCK, and the concentrations of absorbed nutrients in portal plasma, which can be expected to influence animal performance.