Milk-Ejection Activity (Oxytocin) in the External Jugular Vein Blood of the Cow, Goat and Sow, in Relation to the Stimulus of Milking or Suckling

Abstract

Milk-ejection activity (oxytocin) was assayed in the external jugular vein blood of cows, goats and sows during milking or suckling. The hormone was extracted from blood plasma by gel filtration, followed by lyophilization and then assayed in the lactating guinea-pig by the increase in intramammary pressure after intra-arterial injection.Serial blood samples were taken during machine milking of cows which had been accustomed to the milking routine and blood sampling procedure. The stimulus most consistently followed by a transient appearance of oxytocin in the jugular vein blood was the application of the teat cups. In some cases, there was a second release of oxytocin, later in the milking process, unrelated to any apparent stimulus. There was no evidence in these experiments of any conditioning of oxytocin release to visual, auditory or olfactory stimuli associated with the milking routine.Serial blood samples were taken during hand-milking of goats which had been accustomed to the milking routine and blood sampling procedure. Oxytocin was detected in jugular vein blood in only a minority of experimental milkings. Irrespective of whether oxytocin was found in the jugular blood the milk yield at the experimental milking did not differ appreciably from the value to be expected from comparable milkings for the preceding week.Serial blood samples were obtained from sows during suckling, the animals having been accustomed to the presence of the experimenter and the blood sampling procedure. In most of the experimental sucklings oxytocin was found in the blood. The occurrence of the hormone was transient and it was usually released just before the milk-ejection phase.In most of the cases in which no hormone was detected in the blood the piglets obtained no milk as judged by their behaviour.The results suggest that in the cow and sow the milk-ejection reflex is a neurohormonal reflex involving the release of oxytocin. On the other hand, in the goat, provided the animals are carefully hand-milked, normal milk yields can be obtained without the release of oxytocin.

The milk ejection reflex in the pig

“…Briefly, each milk ejection was observed only after a period of suckling that was initiated either by the mother or by the piglets. As seen by other workers (Gill &r Thomson, 1956;Folley & Knaggs, 1966;Fraser, 1977;Whatson &r Bertram, 1980), we could broadly distinguish several phases in the suckling behaviour of the piglet: first, the whole litter started jostling for the teats and nosing vigorously at the udders; then a phase of quiet suckling followed, which gave place to final phase of rapid suckling and nosing at the udders, at the end of which the piglets usually went away from their mother. 589 F. ELLENDORFF, M. L. FORSLING AND D. A. POULAIN Our records showed unequivocally that the beginning of the phase of quiet suckling was coincident with the onset of the rise in intramammary pressure.…”

“…589 F. ELLENDORFF, M. L. FORSLING AND D. A. POULAIN Our records showed unequivocally that the beginning of the phase of quiet suckling was coincident with the onset of the rise in intramammary pressure. Milk ejection appears therefore to follow the phase of initial massage of the udders, as suggested by some authors (Gill & Thomson, 1956;Folley & Knaggs, 1966) and not as behavioural observations indicated, the phase of quiet suckling (Whittemore & Fraser, 1974). The brief period of quiet suckling, lasted 7-38 sec (Folley & Knaggs, 1966, 13-58 sec;Whittemore & Fraser, 1974;4-45 sec) and corresponded to the duration of the alterations in the intramammary pressure (range 8-41 sec).…”

“…Once the period of slow grunting was established, serial samples were collected until the milk ejection and/or the suckling period were finished. A rise in plasma oxytocin has been reported (Folley & Knaggs, 1966), but its precise relation to milk ejection, detected by visual observation only, could not be clearly established. In the present study, hormone assays showed that rise in intramammary pressure was preceded by some 30 sec by the appearance of large amounts of oxytocin in the jugular vein.…”

“…A number of aspects of the milk ejection reflex in the pig have been described, such as the behaviour of the mother and her piglets (Gill & Thomson, 1956;Fraser, 1973Fraser, , 1975Whittemore & Fraser, 1974;Whatson & Bertram, 1980), the effect of oxytocin or vasopressin on the mammary gland (Whittlestone, 1952(Whittlestone, , 1953(Whittlestone, , 1954a or the plasma concentration of oxytocin during suckling (Folley & Knaggs, 1966;Forsling, Taverne, Parvizi, Elsaesser, Smidt & Ellendorff (1979). The present study was designed to give a more comprehensive picture of the milk ejection reflex in the sow.…”

Electrophysiological evidence for the activation of supraoptic neurones during the release of oxytocin

“…Four of the phasically active units were correlated with the oxytocin release for milk ejection. Three of these units displayed a burst of activity superimposed on the terminal portion ofan active phase, some 10 2-14*7 see INTRODUCTION The neurosecretory cells of the paraventricular (PV) and supraoptic (SO) nuclei of the hypothalamus have axons projecting to the neurohypophysis and form the efferent pathway for the neuroendocrine reflexes involved in the release of oxytocin and vasopressin following stimuli such as suckling (Folley & Knaggs, 1966;Bisset, Clark & Haldar, 1970), expansion of the birth canal (Roberts & Share, 1968;Haldar, 1970), dehydration (Jones & Pickering, 1969) and haemorrhage (Ginsburg & Brown., 1956;Bisset, Clark & Errington, 1971). PV and SO units have been identified in many studies by antidromic activation from the neurohypophysis (Yagi, Azuma & Matsuda, 1966;Cross, Novin & Sundsten, 1969) and the characteristics of their antidromic activation have been extensively investigated by extracellular (Dreifuss & Kelly, 1972a, b;Negoro & Holland, 1972;Barker, Crayton & Nicoll, 1971) and intracellular recording (Koizumi & Yamashita, 1972).…”