[Changes in the conditions of milk extraction as affected by a beta mimetic (isoprenaline) administered by intrajugular route during mechanical milking of cows]. / Modifications des conditions d'extraction du lait sous l'effet d'un beta-mimétique (isoprénaline) administré par voie intrajugulaire pendant la traite mécanique de la vache.

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.