Paper - Oestrus and ovulation in swine (1917)

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Corner GW. and Amsbaugh AE. Oestrus and ovulation in swine. (1917) Anat. Rec. 12: 287-.

Online Editor  
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This historic 1917 paper by Corner and Amsbaugh is an early description of the pig reproductive cycle.

Also by this author: Corner GW. Maturation of the ovum in swine . (1917) Anat. Rec. 13(2): 109-112.

Modern Notes: estrous cycle | pig

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Oestrus and Ovulation in Swine

George W Corner (1889 - 1981)
George Corner (1889 - 1981)

George W. Corner and A. E. Amsbaugh

From the Anatomical Laboratory of the University of California

  • We hope to have an opportunity to express fuller thanks to Mr. Snyder and the gentlemen of the U. S. Inspection service at the South San Francisco plant, in connection with other studies to appear somewhat later, the material for which has been obtained through their immediate assistance.

I. The Period Of Ovulation

It seems remarkable that almost nothing should be known of the process of ovulation or of the mature ovum of the pig, which has for many years been in constant use for the investigation and teaching of mannnalian embryology. In so thorough a review as Marshall's 'Physiology of Reproduction' ('10) there is only a meagre note:

It is probable that the sow ovulates during oestrus and not during the pro-oestrum, since it is stated that sows are most successfully served on the second or third day of 'heat.' Coition, if it occurs earlier, is frequently not followed Jjy conception. From Hausmann's description (1840) it would seem that ovulation does not take place prior to coition, but this statement has not been confirmed.

That ovulation occurs at or near the time of oestrus is stated in Keibel's Normentafeln ('97) and is of course implied in Assheton's studies on the early development of the pig ('98), but the precise relation of the two events has never been fully worked out.

To obtain exact information upon this point we have undertaken the observations here reported. They ha\'e been made possible through the generous cooperation of Mr. J. 0. Snyder, of the Western ]\Ieat Company, San Francisco,' and of ]Mr. Ralston B. Brown, Superintendent of the Oakland Meat and Packing Company's plant in West Berkeley, and his staff. Through ]\Ir. Brown's kindness permanent laboratory space had already been provided at the packing house; for this work we were allowed free access to the stockyards at all hours, and upon occasion animals weve killed out of the regular order for us.

The females of the wild swine of Europe are monoestrous, according to Kaeppeli ('08), having but one period of heat in the year; but under domestication the sow becomes polyoestrous, coming in heat at intervals of two to four weeks, usually about every twenty-one days, as all breeders agree. The period of heat commonly lasts three days and is characterized by sexual excitement and in some individuals by swelling, reddening, and slight eversion of the \'ulva, or even at times by a serous, mucous, or partially sanguineous discharge from the genital orifice. If a boar be present, the sexual excitement is made apparent by ready acceptance of coitus, which is denied at all other times; if none but females are in the pen, the sow in heat will be seen to sniff at the genitals of her neighbors and 'ride' them in imitation of coitus. Frequently the sow is the recipient, rather than the donor, of these attentions. The period is not terminated by coitus, but continues until the end of three days.

In order to distinguish these sows from others in the cori'als until the time of butchering, they were marked with a daub of white paint thoroughly rubbed into the hair of the back between the .shoulders. Immediately after evisceration, the Fallopian tubes were removed by cutting across the upper portion of the uterine horns, were carried to the laboratory in 0.7 per cent saline solution, and there washed out by inflating them with salt solution through a slit in the wall near the fimbriated extremity. After inflation with the fluid, the tubes were gently 'milked' into a Syi-acusc dish, and the washings examined with the dissecting jnicrosco])e. This simple and ahnost infallible method of finding the ova was suggested to us by Professor Evans as an improvement on Martin Barry's practice of milkhig the tube without hijected tUiid {"A\)). As we have sul)se(iuently found it h.'id been used by 8obotta and no doubt others as well.

Our series includes ten animals wliich wow m heat on the day of killing of the day before. In ci^ht of vitro the Graafian follicles had ruptured and we were able to recover some or all of the ova from the tubes m each case. Of these eight sows, six were killed on the second or third day of the period, one between sixteen and thirty-nine hours after the onset of heat, and one between thirteen and twenty-two hours after the beginning of oestrus. In two of the ten there were large Graafian follicles, all unruptured except one follicle in one of the sows, which had apparently just collapsed. Unfortunately we have no record as to the time of onset of heat in these two animals, but the conditions in the other eight show that ovulation had occurred during oestrus, and probably on the first or second day of the period.

II. ovrLA'irox si'oxTAXEor.s ix Tin: sow

During the discussion which arose over Born's and Fraenkel's suggestion that the corpus luteum exercises the function of inducing ovulation at regular periods, a distinction was drawn between those mammals in which ovulation is spontaneous, and those in which copulation is necessary to invoke rupture of the follicles. Villemin ('08) maintained that ovulation is spontaneous in all mammals, but Ancel and Bouin ('09) state, on the basis of personal researches (details of which are not given) that ovulation is spontaneous in the human species and in other primates, in the dog, horse, cow, and pig; in the rabbit, guineapig, mouse, and cat rupture ensues only after coitus. The work of Marshall and Jolly ('06) on the dog and Heape ('97) on the mare, are in agreement with the results of Ancel and Bouin, and to the first mentioned class we may also add the sheep (Marshall '03) and the rat, according to Sobotta and Burckhard ('10) conlirmed and extended by the recent carefully gathered data of Long and Quisno ('16). The placing of the rabbit in the second class has been confirmed by Regaud and Dubreuil ('08); the cat by Longley ('11); and Marshall ('04) has added the ferret to the list. The mouse, however, belongs to the class in which ovulation is spontaneous (Tafani '89, Sobotta '95) and also the guinea-pig (Loeb '11).

The only mention of the sow in this regard is the statement of Hausmann ('40) quoted above from ^Marshall ('10) that in this species ovulation is not spontaneous. On the contrary, our specimens show clearly that in swine coitus is not necessary for rupture of the Graafian follicles, for we have records of ten sows in which ova were found in the tubes although no boars had been in the pens with them. ]\Ir. Brown informs us that according to the conditions of shipment of the live-stock, it is very milikely that these animals had the opportunity to copulate before arri^'ing at the stock^^ards. Two of the sows were under observation before oestrus set in, and are therefore even more definiteh" known not to have copulated. ^Moreover, in an anunal in which but one follicle of many had ruptured, copulation had been observed sixteen hours previously. Ovulation, therefore, is independent of copulation.

III. The Mature Ovum

Little or nothing has been known of the mature ovum of the sow, and we have found no record of any previous observation of the unsegmented ova from the tube. Assheton's earliest specimens were already in the two-cell stage ('98). Lowrey ('11), in his stud3^ of the prenatal growth of the pig, attempted to estimate the size and weight of the mature ovum by allowing a slight addition to the diameter of the largest ovarian ovum he found, which measured 177 micra, with a zona pellucida 10 micra in thickness. He estimated, therefore, that the mature ovum would have a diameter of 180 micra. We liaA'e measured fouiteen fresh tubal ova from nine sows, and find the diameter, including the zona pellucida, to vary from 155 to 165 micra, the zona being about 10 micra in thickness. The ova are plainly visible with the naked eye if placed against a strong light. We have not noticed a radial striation of the zona pellucida either in fresh or fixed ova. The ovum is filled with yolk granules of varying sizes, usually about three to five micra in diameter, which are so numerous antl so refractile that they quite conceal the nucleus. A ])()lar body may often be seen very clearly.

The ova are usually naked, but may be covered by the cells of the corona radiata, or even by a considerable portion of the discus proligerus.

A few of the ova which have been sectioned, seem to show no deviation from the usual process of maturation in other mammals; the first polar body and the second polar spindle are formed in the ovary, and the second polar body seems to be formed after fertilization. In each of two sows killed on what we believe to be respectively the sixth and eleventh days after the onset of oestrus, we were surprised to find a degenerating ovum in the tube.

In three sows in which coj^ulation had occurred, fertilized ova were found. They all chanced to be in the same stage, just before fusion of the two pronuclei, and are therefore the earliest embryos of the pig yet reported.

The ovaries and uteri of these animals are naturally of the greatest interest, and studies of them are now in progress.


  1. In the domestic sow, ovulation occurs during oestrus, probably on the first or second day.
  2. Ovulation is independent of coitus.
  3. The mature unfertilized ovum of the sow measures 155-l()o micra in diameter, has a zona pellucida about 10 micra thick, and a yolk heavily laden with fat.
  4. Fertilization of the ovum occurs in the Fallopian tube, as in other mammals.

Literature Cited=

Ancel, p. and Bouin, P. 1909 Sur les homologies et la signification des glandes b secretion interne de I'ovaire. C. R. Soc. de Biologic. Paris, T. 67,

p. 464. AssHETON, R. 1898 The development of the pig during the first tea days. Quarterly Journal of Microscopical Sciences, vol. 41, p. 329.

Barry, M. 1839 Researches in embryology. Philosophical Transactions, pt. 1, 1839.

Hausmaxx, U. F. 1840 I'eber die Zeugung und Entstehung des wahren weib lichen Eies. Hannover (quoted by Marshall, 1910).

Heape, W. 1897 The artificial insemination of mammals. Proc. Royal Society, vol. 61, p. 52.

Kaeppeli, I. 1908 Beitrage zur Anatomie und Physiologic der Ovarien von wildlebenden und gezahmten Wiederkauern und Schweinen. Berne, dissertation.

Keibel, F. 1897 Normentafeln zur EntAvickelungsgeschichte des Sclnveines. Jena.

Loeb, L. 1911 The cyclic changes in the ovary of the guinea-pig. Jour. Morph., 22, p. 37.

Long, J. A. axd Qui.sno, J. E. 1916 The ovulation period in rats. Science, N. S., vol. 44, p. 795.

Longley, W. H. 1911 Maturation of the egg and ovulation in the domestic cat. Am. Jour. Anat., vol. 12, p. 139.

LowREY, L. G. 1911 The prenatal growth of the pig. Am. Jour. Anat., vol. 12, p. 107.

Marshall, F. H. A. 1903 The oestrous cycle and the formation of the corpus luteum in the sheep. Philosophical Transactions of the Royal Society, B, vol. 196, p. 47.

Marshall, F. H. A. 1904 The oestrous cycle in the common ferret. Quarterly Journal of Microscopical Science, vol. 48, p. 323.

1910 The Physiology of Reproduction. London.

Marshall, F. H. A. and Jolly, W. A. 1906 Contributions to the physiology of mammalian reproduction. Part I: The oestrous cycle in the dog. Philosophical Transactions of the Royal Society, B, vol. 198, p. 99.

Regaud, Cl. and Dubreuil, G. 1908 L'ovulation de la lapine n'est pas spon tanee. C. R. Soc. de Biologic, Paris. T. 64, p. 552. SoBOTTA, J. 1895 Die Befruchtung und Furchung des Eios dor Maus. Archiv fur Mikroscopische Anatomie, vi.l. 45, S. 15.

SoBOTTA, J. AND BuRCKHARD, J. 1911 Rcifung und Befruclituiitii; des Eies dor weissen Ratte. Anatomische Hefte, 42, S. 433.

Tafani, a. 1889 I primi moment! dello svilluppo dei maminiferi. Atti d. R. instituto di stvid. super, prot. c. di pcrfezion, Fironzc. (Quoted by

Sobotta '95). Villemin, F. 1908 Sur les rapports du corps jaune avcc la menstruation ct Ic rut. C. R. Soc. de Biologic, T. 64, p. 444.

Cite this page: Hill, M.A. (2020, September 22) Embryology Paper - Oestrus and ovulation in swine (1917). Retrieved from

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