Arieli, A., Fac. Agric., Food and Environ. Sci., Department of Animal Sciences, Rehovot 76100, Israel
Abramson, S., Fac. Agric., Food and Environ. Sci., Department of Animal Sciences, Rehovot 76100, Israel
Mabjeesh, S.J., Fac. Agric., Food and Environ. Sci., Department of Animal Sciences, Rehovot 76100, Israel
Zamwel, S., Fac. Agric., Food and Environ. Sci., Department of Animal Sciences, Rehovot 76100, Israel
Bruckental, I., Institute of Animal Science, Agriculture Research Organization, Volcani Center, Bet Dagan 50250, Israel

The effect of infusing similar energy equivalents of starch into the rumen, or starch or oil into the abomasum was studied in four midlactation cows in a 4 × 4 Latin square design experiment; controls were ruminally infused with water. Cows were fitted with cannulas in the rumen, abomasum, and ileum, and nutrient digestion in the rumen and small intestine was evaluated with Cr as a digesta marker. Ruminai infusions of starch, or abomasal infusions of starch or oil, were associated with a decrease in voluntary feed organic matter intake. Overall energy intake was reduced in oil-infused, but not in starch-infused cows. Nonstructural carbohydrate digestibility in the rumen and in the small intestine was similar among treatments. In abomasally infused cows 3.4 kg/d of nonstructural carbohydrates was apparently digested in the small intestine. Milk production was reduced in oil-infused cows, but the efficiency of milk energy and protein yield was unaffected by treatments. Plasma glucose, insulin, and IGF-1 concentration, mammary glucose extraction rate, rumen ammonia and plasma urea, and arterial and mammary extraction rate of amino acids were all similar among treatments. Large quantities of starch can be digested in the rumen or small intestine of dairy cows. There appear to be no metabolic advantage to increasing the supply of starch to the rumen or the abomasum of mid-lactation dairy cows maintained on highly concentrated diets and exhibiting a positive energy balance.