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

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 the first trial, an average of 2.15 kg of glucose (per cow) was infused daily for 5 days. Compared to the control treatment (water infusions), the glucose infusions increased glucose concentrations of plasma (65.93 to 70.27 mg/100 ml) but had no significant effects on insulin in plasma. Milk yield increased 1.9 kg per day while the percentages of milk fat and protein decreased slightly (.31 and .14) as a result of glucose infusions. However, daily yields of milk fat and protein were not affected significantly by the increased availability of glucose. In a second trial, propionate (15 moles/cow/ day) was infused into the abomasum continuously for 5 days. Feed intake was reduced 2.53 kg per day during propiohate infusions. Milk yield, milk composition, and glucose and insulin concentrations in plasma were not affected by postruminal infusions of propionate.