Impact force as a possible cause of mechanical transfer of bacteria to the interior of the cow's teat

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Abstract
Summary Using bacterial endotoxin as a tracer material, it has been shown that a jet of liquid impinging on the end of the teat for 1 min after milk flow had ceased during machine milking could force material past the barrier of the streak canal. Positive results were obtained when the maximum pressure at the centre of the impact area was about 0·25 bar, with a considerably higher frequency of positives at 0·3–0·5 bar. It seems possible that such impact pressures might occur during milking and cause transfer of infective material to the teat sinus. Impact force could arise when milk returned to the teatcup liner as the result of local or general conditions of instability in the milking machine vacuum.