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Influence of contractility of papillary sphincter muscle on penetrability of the papillary duct in the bovine quarter after machine milking.

It has been suggested that machine milking causes the papillary sphincter muscle (teat sphincter muscle) to relax or to stretch and therefore increases the probability of successful penetration of the papillary duct (streak canal) by microorganisms. To determine the potential for contractile tension of the papillary sphincter muscle to influence penetrability of the papillary duct, selected quarters of individual cows were treated to cause the sphincter muscles to contract at 10 minutes after milking. All quarters were then subjected to a penetrability assay. To cause the papillary sphincter muscles to contract, 1 quarter was dipped into ice water and a 2nd quarter was squeezed twice at the papillary tip. Ice water increases base-line contractile tension and squeezing induces 1 or more rhythmic contractions of the teat sphincter muscle. To measure penetrability, Escherichia coli endotoxin (1 microgram in 2.5 microliters of distilled water; type O128; B12) was inserted 3 mm into all quarters. A 3rd teat was then squeezed at its tip. The 4th teat served as a control. This procedure was repeated for 5 days or until individual quarters responded in terms of a precipitous increase in the Wisconsin mastitis test score. Of a total of 345 observations, chi 2 analysis indicated that the proportion of responsive quarters was the same for each of the 4 treatment groups. Overall, it would seem that the contractile state of the teat sphincter muscle after milking does not significantly affect penetrability of the papillary duct, at least in terms of a solute, such as endotoxin. However, in a subset of animals, pretreating teats to increase contractile tension actually enhanced penetrability.