Mammary and whole animal metabolism of glucose and fatty acids in fasting lactating goats

Abstract

SUMMARY1. Measurements were made of milk yield, mammary blood flow and mammary arteriovenous differences during the measurement of substrate entry rate by the isotope dilution method using [U-14C] acids at 094-6-8 mg/min/kg and 6-9 % of total CO2 was derived from each. The udder took up 3-0-5*7 mg/min/kg of tissue and 4-8 % of mammary CO2 was derived from each acid. In the udder 8 and 5-5 % of stearate and oleate were oxidized and 25 % of palmitate. Mammary uptake of stearate was 31-5 % of the total entry rate, palmitate 1 %, and oleate 7-5 %. Only long chain milk fatty acids were labelled. 6. During fasting the mammary R.Q. was 0-85 + 0 045 compared with a value in fed animals of 1-24 + 0-02, when the udder is synthesizing fatty acids from acetate. The total mammary uptake of lipid precursors was only 74 % of the rate of milk fat secretion and there was an 18 % shrinkage in empty udder volume, suggesting the use of endogenous mammary tissue substrates.

Plasma acetate turnover and oxidation.

“…In contrast, in the ruminant animal in the fed state, plasma acetate oxidation contributes 30-60% of the total CO2 output (3,20,21). After a 24-h fast, however, plasma acetate oxidation accounts for 10% or less of the CO2 output (4,22), which is similar to our observations in the overnight fasted human.…”

Effects of substitution of dietary protein with carbohydrate on lactation performance in the mink (<i>Mustela vison</i>)

“…During lactation, glucose is an important intermediate in the metabolism as precursor in lactose synthesis, and an adequate supply is essential for milk secretion (Annison et al, 1968). Borsting and Damgaard (1995) found that lactating mink fed a diet with 12% of ME derived from carbohydrates had to provide about 75% of their glucose requirement by gluconeogenesis.…”

Modeling energy and protein reserves in support of gestation and lactation: glucose as a limiting metabolite in caribou and reindeer

“…At higher rates of milk secretion, approaching 2 L/d, the supply of glucose precursors for lactose synthesis can limit lactose synthesis (White & Luick, 1976). In turn, the rate of lactose synthesis exerts a strong control over the level of milk production in ruminants (Annison et al, 1968). us, whenever dietary glucose precursors cannot meet glucose demands the LPR is tapped.…”