Mammary arterial and venous concentrations of serum insulin in lactating dairy cows

SummaryInsulin averaged 2.6 ng/ml in mammary arterial and venous sera collected from 30 min before to 70 min after milking of cows lactating 5-12 weeks. During the same period in cows lactating 37-57 weeks insulin increased to 3.5 ng/ml. Milking did not affect insulin concentrations during early or late lactation. Arteriovenous (A-V) differences averaged 0.17, 0.14 and 0.22 ng/ml for 30 min before, 0-20 min after and 30-70 min after milking. Stage of lactation (and yield of milk) did not affect A-V differences. Mammary uptakes of insulin averaged 1.6 and 1.4 μg/min in early and late lactating cows, respectively. Maintenance of uptakes of insulin may be associated with uptake of metabolites essential for maintenance of lactation.