Cardiovascular responses of cows given electrical current during milking.

Six Holstein cows in late lactation were used to determine effects of 4-mA square wave alternating current on mammary gland blood flow rate, heart rate, and blood pressure. Current to the lumbar-sacral region of the cows' back was applied 10 s prior to udder massage and throughout milking. Heart rate was measured from systolic pulses (beats/min) off strip chart recordings. Blood pressure determinations were made from carotid arterial cannulae. A single rise in blood flow rate occurred during milkings without current. Mammary blood flow increased (30% with respect to rest) without 40 s of milking. Heart rate and blood pressure did not change significantly. An abrupt increase in mammary blood flow rate, heart rate, and blood pressure was seen immediately upon current application prior to milking. Mammary blood flow rate increased 50%, heart rate 25 beats/min, and blood pressure 33 mm Hg. The response latency was approximately 60 s. A second rise in mammary blood flow (31%) was milking induced, occurring within 42 s of milking machine attachment. Milk yield was not influenced by current. Our data suggest that 4-mA of alternating current, applied prior to and throughout milking, causes an immediate elevation in mammary blood flow rate, heart rate, and blood pressure of cows. Cardiovascular responses are short-lived. Current given throughout milking does not influence normal physiological changes in mammary blood flow during milking.