Determination of Contained-Milk Volume of the Mammary Gland of the Goat by 141Cerium and 14C-Peg-4000

Abstract

Cerium-141 and 14C-polyethylene glycol, molecular weight 4,000, were used in an isotope dilution technique to determine the volume of milk in the mammary gland of the goat. Procedures included introduction of label into the mammary gland by way of the teat meatus and an intravenous injection of 2 IU of oxytocin followed by hand manipulation of the udder to facilitate uniform mixing of cistern, duct, and that portion of the alveolar milk let down in response to the oxytocin. Assay of any size milk sample taken after this procedure allows approximation of the mammary gland–contained milk volume at the time of the oxytocin dose.Results were consistently the same for both 141Ce and 14C-polyethylene glycol, allowing the option of using either label in the technique. Recover of both labels was essentially 100% 3 days after dosing the udder, and no 141Ce was detected in blood or urine within 24 hours. Label was distributed uniformly among serial samples of the milk readily collectable after the mixing procedure, representing 87.9% of the computed total milk volume. A portion of the residual milk recovered with a second dose of oxytocin showed 141Ce and 14C-polyethylene glycol amounts similar to those of the milk already collected.