Glucose metabolism and milk yield of cows infused abomasally or ruminally with starch

The effect of ruminal or abomasal starch infusion on milk yield and glucose metabolism of early lactation cows was measured. Four cows were continuous ly infused in the rumen or abomasum with partially hydrolyzed starch (1500 g/d) or were not infused (control) for three 14-d periods during wk 4 to 12 postpartum. Milk yield averaged over 40 kg/d throughout the experiment. Mi lk and milk lactose yields tended to increase when starch was infused and D MI was decreased, regardless of the site of infusion. Starch infusion incre ased mean insulin concentration and tended to decrease the concentration of serum nonesterified fatty acids. Ruminal starch infusion did not affect gl ucose irreversible loss rate but tended to increase glucagon concentration and decrease glucose oxidation. The increased milk yield that occurred when starch was infused ruminally relative to the milk yield of control cows co uld be a result of increased microbial protein supply or increased energy a vailability. Compared with ruminal starch infusion, abomasal starch infusio n tended to increase the irreversible loss rate of glucose and to increase glucose oxidation. Abomasal infusion tended to increase plasma insulin conc entration and to decrease the nonesterified fatty acid concentration relati ve to ruminal infusion. Infusion of starch abomasally resulted in increases of most uses of glucose, including milk lactose production, glucose oxidat ion, and the possible storage of glucose as body fat, which indicates that the early lactation dairy cow has a greater capacity for glucose metabolism than is provided by voluntary feed intake of average diets, but that not a ll available glucose is partitioned to the mammary gland. These data should be useful in testing current concepts and equations in nutritional and met abolic models of dairy cattle.