Effects of Abomasal Infusions of Glucose and Proprionate on Milk Yield and Composition

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Abstract
According to the glucogenic theory increased glucose availability is responsible for the low-milk fat problem that occurs when cows are fed high-grain, low-fiber diets. Abomasal infusions of glucose or propionate were used to test this theory. In trial 1 an average of 2.15 kg of glucose/cow was infused daily for 5 days. Compared to the control treatment (water infusions), the glucose infusions increased glucose concentrations of plasma (65.93-70.27 mg/100 ml) but had no significant effects on insulin in plasma. Milk yield increased 1.9 kg/day while the percentages of milk fat and protein decreased slightly (.31 and .14) as a result of glucose infusions. Daily yields of milk fat and protein were not affected significantly by the increased availability of glucose. In trial 2, propionate (15 mol/cow per day) was infused into the abomasum continuously for 5 days. Feed intake was reduced 2.53 kg/day during propionate infusions. Milk yield, milk composition, and glucose and insulin concentrations in plasma were not affected by postruminal infusions of propionate.