Effect of teat stimulation on sympathetic tone in bovine mammary gland.

Rate of contraction of teat sphincter muscle in cows is partially under sympathetic control. To investigate the effect of teat stimulation on sympathetic tone in the mammary gland, rates of spontaneous rhythmic contractions of teat sphincter muscle were measured prior to and during eight machine milkings by pressure transponding devices. Transponding devices were inserted into right front and right rear teat ducts. After a 5-min control, the udder was prepped for 1.5-min, the right front transponder was removed, and then the left front, left rear, and right front quarters were milked while contractile frequency of the right rear sphincter muscle continued to be monitored. During the control period, teat sphincter muscles contracted with a nominal frequency of from two to four per min. Rhythmic contraction of the teat sphincter muscle decreased by about one per min during manual stimulation of the udder. Toward the end of milking, rates reached a low, and in half of the trials there were no contractions. After milking, with teats no longer stimulated, contractile frequency rose towards baseline in the unmilked right rear quarters. This decrease in rate of contraction is likely from a decrease in sympathetic tone in the mammary gland resulting from an autonomic reflex to teat stimulation.