Ionized calcium in milk and the integrity of the mammary epithelium in the goat.

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Abstract
Injection of citrate or EGTA [ethylene glycol-bis (.beta.-amino ethylether)N,N,N'',N''-tetraacetic acid] solutions into the lumen of the mammary gland of goats in quantities sufficient to reduce ionized Ca to less than 1/10 of normal, led to increases in milk concentrations of Na and Cl and decreases in K and lactose. Subsequent milk yields were decreased in glands treated with citrate but not in those treated with EGTA. Blood-milk potential difference decreased (i.e., towards zero) in glands in which citrate was present. In goats milked hourly with the aid of oxytocin, milk Na and Cl concentrations increased while K and lactose decreased; there was no apparent decrease in Ca2+ concentration. Ionized Ca in milk is essential to preserve the integrity of the mammary epithelium during lactation.