[Changes in the conditions of milk extraction as affected by a beta mimetic (isoprenaline) administered by intrajugular route during mechanical milking of cows].

Between days 80 and 105 of lactation, 11 FFPN cows (table 1) received an intrajugular injection of either 0.9% NaCl or 0.3 mg of isoprenaline (IPN = beta-receptor agonist). Each of the two treatments was repeated at least 7 times by giving NaCl and IPN on successive, alternate days. IPN: - did not change either the total milk yield of the morning milking (13.5 l vs 13.37 l with NaCl) or the volume of milk obtained by stripping (0.460 l vs 0.447 l with NaCl), although individual responses varied considerably (table 3); - significantly increased milk flow by about 25% because it reached 1.144 l/min/quarter after IPN administration vs 0.929 l/min/quarter after NaCl injection (table 4). These results confirm our previous observations concerning milk loss between milkings (Bernabé and Peeters, 1980), i.e. the stimulation of smooth muscle beta-receptors enhances milk flow.