Changes of blood catecholamine levels in the sheep during machine milking

Abstract

Various stimuli such as emotional stress, fright, anxiety, pain, embarrassment and discomfort inhibit milk ejection. These stimuli activate the sympathetic and sympathetico-adrenal systems. The release of significant amounts of catecholamines in the animal economy may be shown by inhibition of milk ejection. This inhibitory effect of catecholamines is attributed either to central neural mechanisms (Cross, 1955; Denamur, 1965; Sibaja & Schmidt, 1975;Tribollet et al. 1978;Barowicz, 1979) or to peripheral alterations. The peripheral inhibitory effect acts either by vasoconstriction (Linzell, 1955; Cross & Silver, 1962) or by an intrinsic action of catecholamines directly upon the myoepithelium (Chan, 1965; Bissett, Clark & Lewis, 1967; Vorherr, 1971;Ewye«aZ. 1975).Although much work has been done on the mechanism by which catecholamines are released, little attention has been given to the mechanism of catecholamine release during the milking process, so that it seemed of interest to estimate the catecholamine levels in the blood plasma of the sheep during machine milking. The half-life of exogenous adrenaline (A) and noradrenaline (NA) in the circulation has also been determined. METHODSEight Friesian sheep (50-55 kg) in the first lactation were used for the experiments, of which 3-4 were made on all animals between the first and third months post partum. Milking was done with our portable unit, operated at a vacuum of 46-50 kPa with a pulsation ratio of 3:1, at 170-190 cycles/min. The lambs had been withdrawn from their dams 12 h before milking began. During milking the ewes were fed concentrates ad lib. The animals were accustomed to the milking procedure.Each time, a polyethylene catheter (1-7 x 300 mm) was introduced into the external jugular vein in the off foreleg 30 min before milking. Blood samples of about 18 ml were taken, using a 25-ml glass tube containing 2 ml 1 % EDTA. Blood samples during the milking procedure were taken 2 min before udder washing, during the application of teat cups, and at 30-s intervals during milking. The last sample was collected 5 min after milking was completed. A total number of 8 samples was obtained during the experiment. The time required for collecting a blood sample was about 7-10 s.The biological half-life of exogenous adrenaline Adrenaline-Polfa (Adrenalinum hydrotartaricum) and noradrenaline Levomor-Polfa (l-Noradrenalinum barium) was determined in 4 ewes by performing 4-6 experiments on each animal between the first and second months of pregnancy, when 0-02 mg of these hormones in 20 ml

Central Effects of Catecholamines upon Mammary Contractility in Rats Are Neurally Mediated

“…Thus in the absence of suckling, central P-adrenertic effects would predominate to prevent OXY release and to maintain ductal tone of the mammary glands, uninhibited by ductal mechanoreceptors [10,22] and reinforced by circulating CAs. When suckling is initiated, its action would activate the release of adrenal CAs [10][11][12][13] which would depress the release of OXY [7] and, at the periphery, reduce the access of OXY to the mammary glands and provoke ductal constriction [14][15][16], Also, afferent signals from the mammary glands during suck ling may activate or increase P-adrenergic, neurally me diated control of ductal tone [22, and present study]. As a result of these actions, the latency of milk removal [35,36] would be increased.…”

“…In addition to releasing OXY and other pituitary hor mones, suckling or mammary stimulation also reflexively releases adrenaline (ADR) and NA in rats and other spe cies [10][11][12][13], It is well established that circulating cate cholamines (CAs) inhibit milk ejection by constricting arterioles and mammary ducts within the mammary gland [14][15][16], as well as through a competitive antago nism with OXY at the effector myoepithelium [17]. These latter effects led to the belief that peripheral sympathetic influences had little physiological importance on milk ejection [18] and that their actions were limited to extremely stressing conditions.…”