The correlation between milk yield and mammary uptake of glucose is about 0.93. Low producing cows do not utilize as high a percentage of body glucose as high producers. Infusion of glucose into the dairy cow can increase milk yield. However, this may be partially offset by decreased endogenous glucose availability. Very little glucose makes it past the rumen to be absorbed in the intestine of the ruminant.
Ruminants are particularly dependent upon gluconeogenesis.
Some glucose may be stored in the liver as glycogen, which acts as a readily releasable pool of glucose. However, very little glycogen is left in the liver after the first few days of lactation. The lactose synthesis pathway is shown in the figure below. Another glucose is used for lactose synthesis without modification. The presence of GLUT 1 on teh Golgi membrane apparently is specific to the mammary epithelial cell, as most cells do not have this glucose transporter on the Golgi membrane.