THE CONTROL OF MILK FLOW THROUGH THE TEATS OF DAIRY-COWS

The effects of teat smooth muscles and pulsation on the control of rat e of milk flow have been investigated in two split udder experiments d uring machine milking of dairy cows. When two teats were milked withou t pulsation, the peak flow rate was reduced by .132 kg/min for these t eats and by .107 kg/min for the other two teats, which received good p ulsation. Both of these reductions were statistically significant. Thi s suggests that there is systemic control of the teat sphincter muscle . When systemic muscle control was removed by treatment with clenbuter ol, a beta-agonist, all flow rates increased. However, when the propor tion of the pulsation cycle for which milk flow can occur was consider ed, the actual flow rate for teats milked without pulsation was approx imately 36% lower than that for teats milked with pulsation. This was independent of clenbuterol treatment, suggesting that this local contr ol is independent of overall muscle tone.