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Title: GLUCOSE METABOLISM AND MILK YIELD OF COWS GIVEN ABOMASAL OR RUMINAL STARCH INFUSION

Author
item KNOWLTON, K - UNIVERSITY OF MARYLAND
item Dawson, Tadd
item Glenn, Barbara
item HUNTINGTON, G - NC STATE UNIVERSITY
item ERDMAN, R - UNIVERSITY OF MARYLAND

Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/27/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: High producing dairy cows have a high requirement for glucose, but increasing glucose supply to the mammary gland has not always increased milk yield. Farmers need to know more about feeding diets high in starch content, which provides glucose to the cow. An experiment was conducted with high producing Holstein cows that had starch infused either into their largest stomach, the rumen, or into the true stomach, the abomasum, which is similar to the human stomach. Blood glucose supply was measured using an isotope marker. Starch infusion increased milk yield in cows producing greater than 40 kg/d milk. Starch infused into the rumen did not increase glucose supply to the cow, but did increase glucose breakdown. The increased milk yield was due to something other than starch infusion; likely increased protein supply from the rumen microbes. Starch infused into the abomasum did increase glucose supply and glucose breakdown. The increased milk yield was due to a greater glucose supply. Even so, only 32% of the infused glucose could be accounted for as increased glucose supply. This means that there are other factors limiting use of starch digested in the small intestine. More research is needed to determine these factors. Dairy farmers will observe increased milk yield from cows consuming diets with high levels of ruminally digested starch or bypass starch. Our study showed that the mechanisms by which these diets increase milk yield are different. Also, glucose supply has never been measured in cows at such high levels of milk production. This information will allow farmers, nutritionists and extension workers to accurately formulate rations to maximize energy supply for the cow.

Technical Abstract: The effect of ruminal or abomasal starch infusion on milk yield and glucose metabolism of early lactation cows was measured. Four cows were continuously infused with partially hydrolyzed starch in solution (1500 g/d) to the rumen or abomasum, or no infusion (control) for 3, 14 day periods during weeks 4 to 12 post-partum. Milk yield averaged over 40 kg/d throughout the experiment. Milk yield and milk lactose yield tended to increase with starch infusion, while dry matter intake was decreased, regardless of site of infusion. Starch infusion increased mean insulin concentration, and tended to decrease concentration of serum NEFA. Ruminal starch infusion did not affect glucose irreversible loss rate, but tended to increase glucagon concentration and decreased glucose oxidation. Increased milk yield with ruminal starch infusion relative to control could be a result of increased microbial protein supply or increased energy availability. Compared to ruminal starch infusion, abomasal infusion of starch tended to increase glucose irreversible loss rate, and increased glucose oxidation. Abomasal infusion tended to increase plasma insulin concentration and decrease NEFA concentration relative to ruminal infusion. Increased milk yield with abomasal infusion of partially hydrolyzed starch is more directly attributable to increased glucose supply, but preferential use of glucose for oxidation was indicated.