Effect of site and source of energy supplementation on milk yield in dairycows

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 i n a 4 x 4 Latin square design experiment; controls were ruminally infused w ith water. Cows were fitted with cannulas in the lumen, abomasum, and ileum , and nutrient digestion in the rumen and small intestine was evaluated wit h Cr as a digesta marker. Ruminal infusions of starch, or abomasal infusion s of starch or oil, were associated with a decrease in voluntary feed organ ic matter intake. Overall energy intake was reduced in oil-infused, but not in starch-infused cows. Nonstructural carbohydrate digestibility in the ru men and in the small intestine was similar among treatments. In abomasally infused cows 3.4 kg/d of nonstructural carbohydrates was apparently digeste d in the small intestine, Milk production was reduced in oil-infused cows, but the efficiency of milk energy and protein yield was unaffected by treat ments. Plasma glucose, insulin, and IGF-1 concentration, mammary glucose ex traction rate, rumen ammonia and plasma urea, and arterial and mammary extr action rate of amino acids were all similar among treatments. Large quantit ies of starch can be digested in the lumen or small intestine of dairy cows . There appear to be no metabolic advantage to increasing the supply of sta rch to the rumen or the abomasum of mid-lactation dairy cows maintained on highly concentrated diets and exhibiting a positive energy balance.