Glucose Kinetics in Lactating and Nonlactating Dairy Goats

Abstract

Both intravenous single injections of 6-tritium labeled glucose and primed continuous infusions of uniformly labeled carbon-14 glucose were applied to four nonpregnant Saanen goats. Four sequential treatments were high milk production, low milk production, ``dry``with no milk production, and fasting during the dry period. The diet was 25% chopped alfalfa hay and 75% grain, and by design feed intake decreased sequentally (1.85, 1.49, .80, and 0 kg/day) with the progression from high production to fasting. Glucose irreversible loss averages from single injections of tritium labeled glucose were 199, 169, 96, and 58 mg/min for respective treatments; similar averages from continuous infusions of carbon labeled glucose for the first three treatments were 164, 132, and 76 mg/min, or about 20% less. Other blood glucose kinetic parameters were estimated after single injections, and averages declined from 5.9 to 4.5g for pool size, 315 to 134 mg/min for total entry rate, and 115 to 76 mg/min for recycling as goats went from high production to fasting. Transfer of blood glucose to milk constituents was determined by continuous infusions. Transfer quotients for lactose were 73% for high production and 67% for low production; for casein they were 1.8 andv1.9%. The percentage of glucose irreversible loss accounted for in lactose was 31% for high production and 17% for low production whereas less than .2% was in casein.