Abstract Glucose is the major precursor of lactose synthesis in the mammary gland.
Lactose the major carbohydrate and osmolyte of milk, controls milk volume and its
concentration. Glycosylated haemoglobin (HbG) is a retrospective measure of mean blood
glucose level and it is largely unaffected by recent physiological conditions and
environmental events. The purposes of this study were to determine the correlations
between lactose traits and other milk production traits in dairy cattle and to investigate
whether HbG level can be correlated with milk and lactose production traits. Here, HbG
percentage, milk and lactose production traits including milk yield, lactose, protein, SNF,
total solid and fat percentages and yields were measured in 485 second calved Iranian
Holstein cattle. Statistically significant negative correlations were established between HbG
and milk yield (r=−0.88), lactose yield (r=−0.83), SNF yield (r=−0.81), protein yield
(r=−0.79) and total solid yield (r=−0.74). Positive correlations were established between
lactose yield and milk (r=0.96), protein (r=0.81), SNF (r=0.92) and total solid (r=0.79)
yields. The negative correlation between HbG and milk and total lactose production is probably related to the higher glucose demands in the lactating mammary gland of more
productive cows. The positive correlation between lactose yield and milk, protein, SNF and
total solid yield indicates that the level of lactose synthesis influences milk production traits
in ways other than merely via its osmolytic action