Effects of feeding frequency on glucose concentration, glucose turnover, and insulin concentration in steers

Patterns of diurnal variation of glucose production, utilization, and concentration and of variation of insulin concentration in blood plasma were studied. Four Holstein steers (200 kg) were in a switchback design. Each received 4.6 kg of 70% chopped alfalfa hay and 30% dry cracked corn daily, either as two equal meals at 12-h intervals or 12 equal meals at 2-h intervals. None of mean daily glucose production, utilization, and concentration nor mean insulin concentration was affected by feeding frequency. In response to feeding, insulin was released simultaneously with increased glucose production, suggesting that glucose production and insulin release are regulated by a common effector system. Feeding twice daily resulted in a sinusoidal pattern of glucose specific radioactivity. On the basis of changes of glucose concentration, glucose utilization closely followed production. Within-day variation of glucose production for steers fed twice daily was greater than indicated by variation of glucose concentration. Such variation of production will lead to errors in estimates of glucose production from short (less than 12 h) isotope infusion experiments with steers fed twice daily. Conversely, daily glucose production was not different for steers fed twice or 12 times daily; therefore, frequent feeding is both necessary and appropriate for investigations of glucose kinetics.