Technical note: Therapeutic cessation of lactation of Staphylococcus aureus-infected mammary quarters

The objective of the present study was to compare the ability of chlorhexid ine and povidone-iodine to cause cessation of lactation in Staphylococcus a ureus-infected mammary quarters, assess milk production in the treated quar ter in the subsequent lactation, and evaluate whether microbiological cure was obtained. Fourteen mid- to late-lactation Holstein-Friesian dairy cattl e from the Washington State University dairy herd with single mammary quart er S. aureus intramammary infections were studied. Cows were randomly assig ned to one of two treatment groups, povidone-iodine or chlorhexidine. Cows in the povidone-iodine group were infused with 120 ml of 5% povidone-iodine solution (0.5% iodine) after complete milk-out. Chlorhexidine-treated cows were infused with a proprietary chlorhexidine suspension after two milking s 24 h apart. Treated mammary quarters were not milked for the rest of the lactation. Milk production from each mammary quarter (kg of milk/quarter) w as measured using in-line volume flow meters for 5 consecutive days before treatment and again at the start of the subsequent lactation. Povidone-iodi ne caused permanent cessation of lactation in the treated quarter, whereas 71% of the chlorhexidine-treated mammary quarters returned to function in t he subsequent lactation. Hence, if the primary objective is to eliminate th e mammary quarter from lactation, and thereby presumably lower the risk of herdmates acquiring new S. aureus intramammary infection, then povidone-iod ine appears to be the best of the two methods. No difference in total milk production between lactation one and two in either group was found suggesti ng that permanent loss of a quarter was not detrimental to overall milk pro duction.