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

The effects of teat smooth muscles and pulsation on the control of rate of milk flow have been investigated in two split udder experiments during machine milking of dairy cows. When two teats were milked without pulsation, the peak flow rate was reduced by .132 kg/min for these teats and by .107 kg/min for the other two teats, which received good pulsation. Both of these reductions were statistically significant. This suggests that there is systemic control of the teat sphincter muscle. When systemic muscle control was removed by treatment with clenbuterol, a beta-agonist, all flow rates increased. However, when the proportion of the pulsation cycle for which milk flow can occur was considered, the actual flow rate for teats milked without pulsation was approximately 36% lower than that for teats milked with pulsation. This was independent of clenbuterol treatment, suggesting that this local control is independent of overall muscle tone.