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Cited by 116Neuroendocrine regulation and behaviorAnimal Behavior and Welfare StudiesReproductive Physiology in Livestock

The milk ejection reflex in the pig

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Ellendorff, F., Forsling, M. L., Poulain, D. A.·1982·The Journal of Physiology
DOI 10.1113/jphysiol.1982.sp014470PMC PMC1197265
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Abstract

1. The milk ejection reflex in response to suckling was studied in conscious sows by continuous recording of intramammary pressure, radioimmunoassay of plasma concentrations of neurohypophysial hormones, and observation of the behaviour of the sows and piglets. 2. A regular pattern of nursing, suckling and milk ejection was observed. The mean duration of the suckling period was 6·3 min. Over 144 suckling periods, 113 milk ejections were recorded. Each milk ejection was characterized by a sudden rise in intramammary pressure reaching 20‐49 mmHg, and lasting 8‐41 sec. Milk ejections occurred only once per suckling period, at a mean interval of 44·3 min. 3. Each milk ejection occurred with a mean latency of 2·4 min from the onset of a period of initial massage of the udders by the piglets, and was coincident with a period of quiet suckling when the piglets were consuming milk. The onset of nursing was signalled by the sows grunting in a rhythmic manner. In most cases, the frequency of grunts, at first low, increased suddenly 23 sec before milk ejection. 4. During eighteen suckling periods leading to milk ejection, neurohypophysial hormone assays performed on serial blood samples showed an increase in plasma concentration of oxytocin up to 30 sec before milk ejection. The concentration of lysine—vasopressin did not rise above basal levels. 5. In 21·4% of the suckling periods, no rise in intramammary pressure was observed. In these ‘incomplete sucklings’, the sow usually failed to grunt rapidly, and the piglets obtained no milk. For three of these periods, hormone assay showed no increase in oxytocin or vasopressin concentrations in blood. 6. Oxytocin given intravenously produced variations in intramammary pressure which depended on the dose and the rate of injection. Rapid injections of 25‐50 m‐u. oxytocin, caused milk ejections similar to those induced by suckling. When oxytocin was administered at different rates, the faster the injection, the shorter the latency and the higher the amplitude of the response. Plasma concentrations of oxytocin after injection of 25 m‐u. were similar to those observed during reflex milk ejection. 7. Trains of electrical pulses were applied to the posterior pituitary of four anaesthetized sows. At frequencies of stimulation above 10 Hz, a rise in intramammary pressure and an increase in plasma oxytocin and vasopressin concentrations were observed. At frequencies of stimulation of 30‐50 Hz, the response of the mammary gland and the time course of the variations in oxytocin plasma concentrations were similar to those observed during natural reflex milk ejection. 8. It is concluded that reflex milk ejections during suckling in the pig are caused by the intermittent and spurt‐like release of about 25 m‐u. oxytocin, without concomitant vasopressin release. It is postulated that the release of oxytocin is probably precipitated by a brief and massive activation of oxytocin‐secreting neurones in the hypothalamus. Central mechanisms controlling the intermittent release of oxytocin are discussed.

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Crossref · 10.1113/jphysiol.1982.sp014470

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  • In pigs, suckling evokes increases in intramammary pressure equivalent to those induced by i.v. injection of 50 mU (83 ng) of oxytocin, which for a plasma volume of 5 l would raise plasma concentrations by approximately 17 pg/ml, close to the peak concentration (approximately 18 pg/ml) measured by radioimmunoassay during suckling-induced milk ejection.

    “In pigs (body weight 150–200 kg), suckling evokes increases in intramammary pressure equivalent to those induced by i.v. injection of 50 mU (83 ng) of oxytocin 69. For a plasma volume of 5 l, these would raise plasma concentrations by approximately 17 pg/ml, which is close to the peak concentration (approximately 18 pg/ml) measured by radioimmunoassay during suckling‐induced milk ejection.”

    From Measuring Oxytocin and Vasopressin: Bioassays, Immunoassays and Random Numbers (2016) · cites this paper as [69]

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Authors
Ellendorff, F., Forsling, M. L., & Poulain, D. A.
Venue
The Journal of Physiology
Publisher
Wiley
Published
1982-12
Volume
333
Issue
1
Pages
577-594
ISSN
  • 0022-3751 (ISSN-L)
  • 1469-7793
DOI
10.1113/jphysiol.1982.sp014470
PMC
PMC1197265
OpenAlex
W2161499386
Cited by
116
References
29
Citations by year
2026: 1 · 2025: 2 · 2024: 1 · 2022: 5 · 2021: 2 · 2020: 3 · 2019: 3 · 2018: 4 · 2017: 1 · 2016: 2 · 2015: 1 · 2014: 4 · 2013: 3 · 2012: 1
FWCI
8.53
Type
journal article
Language
en
Open access
Licence
onlinelibrary.wiley.com/termsAndConditions#vor (vor)
Locations
  • The Journal of Physiology (publishedVersion)
  • PubMed Central (publishedVersion)
  • PubMed (publishedVersion)
  • OpenAgrar (submittedVersion)
Topics
  • Social Sciences › Psychology › Social Psychology › Neuroendocrine regulation and behavior
  • Health Sciences › Veterinary › Small Animals › Animal Behavior and Welfare Studies
  • Life Sciences › Agricultural and Biological Sciences › Agronomy and Crop Science › Reproductive Physiology in Livestock
Keywords
milk ejection reflex, pigs, sows, suckling, oxytocin, vasopressin, intramammary pressure, neurohypophyseal hormones, udder massage, oxytocin administration, lactation
MeSH terms
Animals, Behavior, Animal, Female, Lactation, Mammary Glands, Animal, Milk Ejection, Oxytocin, Pituitary Gland, Posterior, Pituitary Hormones, Posterior, Pregnancy, Pressure, Reflex, Swine, Time Factors

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