Quadruplet bovine pregnancy

Keywords: quadruplets, bovine, cow, pregnancy, placenta, allantois, allantochorion

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Old images (~1975) of bovine quadruplets at about 35 days of gestation. This was found in a slaughter specimen where the cervix had been traumatized (and was in a state of healing) and multiple corpora lutea were present in both ovaries. Presumably an attempt had been made to super-ovulate this cow and collect embryos earlier in gestation. Therefore it is unlikely that this pregnancy was the result of spontaneous multiple ovulations. Spontaneous triplets occur in about 1 in 10,000 calvings but quadruplets are so rare that their incidence cannot be accurately reported. Reports suggest that they may occur in about one in a half million calvings.

This specimen was interesting from a two of points of view. First, despite fetal overcrowding, the uterus was able to sustain a quadruplet pregnancy to this stage and second, the fact that the chorions of all four pregnancies had fused yet differential staining of each fetus (methylene blue, clear, dark iodine and light iodine) showed that the allantois of each fetus remained separate. This is shown below.

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Bovine placental anatomy

Keywords: amnion, chorion allantois, bovine, fetus, sexing, tubercle, ultrasound, slip, pregnancy diagnosis

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A bovine fetus at about 50 days of gestation (based on crown-rump length). Note the early formation of the cotyledons, these form opposite the caruncles in the uterus, structures that have been present since the birth of the dam. Together, the caruncles and cotyledons will form "placentomes"; multiple complexes of placental attachment; hence the morphological name of this type of placetation i.e. "muliplex". There is attachment of the fetus at the placentomes at this stage of gestation but it is not firm; this feto-placental unit could easily be removed from uterus.

During pregnancy diagnosis by transrectal palpation at this stage of gestation, it is relatively easy for a practiced operator to lightly grasp the wall of the uterus and the fetal membranes and to let the membranes slip away, feeling its crisp escape from beneath one's fingers. This is known as "slipping membranes".

With regard to the basics of placentation, note that the allantois (the inner sac at the extremities of the feto-placental unit in the top image) is not yet attached to the chorion. Later in gestation, these two membranes will become inseparable and will be known as the allantochorion or less commonly, the chorioallantois. The central, bean-shaped structure is the amnion.

A close up view of the amnion shows how easily the chorion, allantois and amnion can be separated from one another at this stage of gestation. A pair of forceps has been placed under the allantois as it emerges from the amnion (or "...as it emerges from the end of the intra-amnionic umbilical cord"). Proximal to the fetus and within the amnion, the urachus leaves the bladder and runs down the  intra-amnionic umbilical cord, directing urine into the allantois. Unlike horses, ruminants do not have both intra- and extra-amnionic segments of the cord; only intra-amnionic cords.

If one was to separate the allantois from the surface of the amnion (easy to do at this stage of gestation) one would see that the allantois actually crosses the amnion on one side only; like a bridge or belt. This  is shown clearly in the lowest of the three images.

A note on the allanto-amnion and its significance: On the far side of this fetus (and every bovine fetus in this orientation) the amnion is attached to the chorion. Therefore there is no allantochorion on that side of the amnion, only an "allanto-amnion". The allanto-amnion is seldom, if ever, referred to in scientific literature but it does occur and forms a distinct entity of bovine placentation. At term, the attachment of the amnion to the allantois (the allanto-amnion) is firm. The allantois in turn, is firmly attached to the endometrium. This means that the bovine amnion cannot leave the uterus without tearing while the fetus exerts pressure on its caudal-most extremity. Therefore a bovine fetus cannot suffocate in its fetal membranes after birth. Unfortunately the same is not true of horses, where the allantois surrounds the amnion in its entirety, isolating it completely from the chorion. (the allantois covers the outer surface of the amnion and the inner surface of the chorion). Therefore the equine amnion floats freely within the placenta, like a balloon, tethered to the allantochorion by the extra amnionic umbilical cord This allows the equine amnion to leave the uterus intact, covering the face of the equine fetus, causing suffocation. As mentioned, this is impossible in cattle.

Note the pale genital tubercle in this fetus, just under the tail. This is a female. In a male, the genital tubercle would be situated just caudal to the umbilical cord. The situation of the genital tubercles allows fetal sexing by transrectal ultrasound in both cattle and horses at 55 to 60 days of gestation.

Another bovine feto-placenta unit, in this case, exactly 54 days old (according to the breeding date):

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Again, the typical arrangement of the placentomes can be appreciated but when the image is enlarged, the fetal villi can be seen clearly. In other words, the establishment of epithelio-chorial placentation is well underway although the feto-placental unit can easily be separated from the uterus by pulling on it gently.

Older nomenclature held that most bovine placentation was epitheliochorial but presently is is referred to as synepitheliochorial because large multinucleate cells from the chorion invade the epithelium of the maternal placenta (the caruncles) so the chorion ostensibly becomes part of the maternal epithelium ("syn-" < Greek together).

When the chorion was stripped away from the amnion, the allantoic belt that crosses the amnion could be seen clearly. That anatomy is evident below. In this image, the trumpet-like section of the allantois that originates from the urachus, cannot be seen because the fetus has been rolled over to reveal the top of the amnion.

Again, note the prominence of the genital tubercle; another female. Its prominence at this time clearly demonstrates why many fetuses are successfully sexed using transrectal ultrasound at about 55 to 65 days of gestation. In that regard, see this ultrasound image.

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Another female fetus estimated to be approximately 51 days old using the U.Wisconsin Animal Science Fetal Age Calculator.

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In this image, the chorion has been transected along its longitudinal axis, thereby opening the allantois and exposing the amnion (allantoamnion/amnioallantois). As mentioned earlier, there is no allantois between the amnion and chorion over a substantial part of the surface area of the amnion. Therefore, the amnion is fused to the chorion in that area. This allows one to suspend the amnion from the chorion as shown here.

Again, the hook-shaped genital tubercle is very obvious at this stage of gestation, allowing gender determination by transrectal ultrasonography. In the mature female, the genital tubercle will form the clitoris.

Atresia ani. Defecation through vulva

Keywords: atresia ani, calf, bovine

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A three-month-old Holstein calf presented for tenesmus and inability to defecate. This animal had been on a milk replacement diet since birth but began to show symptoms when placed on a solid diet. The animal was euthanized. The external appearance of the perineum suggested partial development of the anus and anal sphincter but the absence of any connection with the rectum. Watery feces had passed through a small fistula connecting the dorsal aspect of the vestibule with the rectum. The vestibule was inflamed but the tract cranial to the hymen appeared to be normal.

At three months of age, there was substantial evidence of follicle development on both ovaries.

Arthrogryposis and placental edema in an IVF calf

Keywords: Arthrogryposis, bovine, IVF, AM, Akabane, lupin

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Arthrogryposis (< Greek meaning "crooked joint") in a Holstein calf obtained through in vitro fertilization (IVF).

The cause of arthrogryposis in this case was not determined and the author is not aware of any reported association between IVF and arthrogryposis. However it is well known that infection by the Akabane and Schmallenburg viruses in all ruminants may cause arthrogryposis. It is also seen when pregnant animals have ingested lupines.

A recessive genetic condition known as Arthrogryposis Multiplex (AM) or “Curly Calf Syndrome” exists in Angus cattle where calves that are homozygous for the AM gene show arthrogryposis.

Interestingly, this calf also showed unusual placental edema, especially in the chorion. In the image below, there appears to be a collection of fluid between the chorion and allantois.

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However, the following image shows that this is not free fluid between the chorion. Instead, the fluid resides within the chorion itself, in the form of edema.

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Placental anomalies have been described in IVF calves before. An interesting case of hydrops of the fetal membranes can be found elsewhere in LORI.  Also, placental anomalies in IVF calves are briefly reviewed in a paper by R. MacDonald: 2011. Hydrops in a heifer as a result of in-vitro fertilization. Can Vet J ;52:791–793.

Uterine leiomyoma in a cow

Keywords: leiomyoma, bovine, uterus, histology


Enlargement seen in the left uterine horn of a pluriparous cow sent to slaughter suggestive of a leiomyoma.

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A close-up view of the transected tumor:

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The histopathology of this tumor was classic for that of a leiomyoma. It was well encapsulated and for the most part, its cells resembled those of normal smooth muscle. No mitoses were seen. In most areas there were whorled fascicles of smooth muscle cells separated by a fibrous stroma:

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In some areas however, the typical muscle fascicles became extensive fields of hyalinized stroma with entrapped smooth muscle cells:

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The incidence of genital leiomyomas is low in cattle, literature suggestion about one in 200,000. By contrast  leiomyomas are among the most common reproductive tumors reported in women and bitches, and are highly estrogen dependent in both. Their dependence on estrogen in cattle is unknown. In cattle, they are found throughout the tubular reproductive tract, even in the cervix.

An intersex bovine animal

Keywords: intersex, hermaphrodite, pseudohermaphrodite

A bovine animal with ambiguous genitalia was a examined by a rDVM (Image acknowledgement & copyright  Mr Max Winkler):

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Although raised as a heifer, the animal did not have a vulva but possessed a rudimentary scrotum and urinated from a vulva-like orifice between the cranial set of four teats.

The animal was sent to slaughter and its tracts sent to the AVC for investigation. Dissection showed the following:

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The ventral aspect of the reproductive tract of an intersex bovine (case pending histology data). Note that this is a high resolution image that can be examined in detail.

This tract was submitted for examination by an interested owner who submitted the animal for slaughter. The animal was ostensibly a fully grown beef heifer close to two years of age. It was seen to urinate from an orifice between the halves of its udder. However, there was no vulva, no scrotum, testes, vulva or vagina. The RDVM was unable to palpate a reproductive tract.

Dissection showed the presence of a long urethra (U) terminating (ExU) between the halves of the udder. There was no hypospadia. Two, well developed seminal vesicles (SeV, histology pending) were present just cranial to the anus and two equally well developed ampullae (Am) arose between the seminal vesicles, terminating cranially  in blind ends in the meso-genital fold. The ampullae entered the colliculus seminalis (CS) in conjunction with openings to the seminal vesicles, approximately where they would be located in a normal male. Attempts to locate a prostate gland (body or disseminate part) were fruitless but small indentations in the lumen of the urethra in the area of the colliculus seminalis suggested an abortive attempt at gland formation in that area.

Ureters (Ur) entered the bladder in their normal position. 

Cranial to the termination of the ampullae, the mesogenital fold continued and although a uterus (Ut) was present, no cervix or uterine body could be identified. The uterus contained a small volume of opaque fluid and the left and right halves of the uterus communicated with one another. The right gonad (G1) resembled an ovary containing a single large follicle/cyst (histology pending). The left gonad (G2) resembled a testis (histology pending) with dense, brown parenchyma.

A close-up view of the ovary-like and testes-like gonads:

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Close examination of the terminal part of the reproductive tract (below) ending between the halves of the udder, showed a vulva-like structure with the corpus cavernosum penis, ending in a clitoris-like structure. The vulva lips are the homolog of the prepuce in females.

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As seen below, the penis in this animal contained a corpus cavernousus, and a urethra that was surrounded (at least partially) by corpus spongiosum urethra. Two small muscle groups present caudally on the penis were presumed to be the retractor penis muscles:

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Interestingly, this animal also had a small scrotum (ringed below) just caudal to the four teats. Not surprisingly, apart from a fat pad, it was devoid of contents.

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Apart from the presence of the large cyst, the right gonad was very similar to the left gonad on histologic examination. The cyst was lined with a single layer of epithelium, not resembling granulosa cells (consistent with a follicle) at all. The nature and origin of the cyst remains unknown; possibly an undeveloped segment of the mesonephric (Wolffian) system. Both gonads showed diffuse masses and cords of cells which resembled interstitial cells in testes (Leydig cells). The wall of the cyst and these cells are shown in the main image below. Within these cords and masses of cells, were small islands of cells circumscribed by thin layers of fibrous tissue. These are shown in the inset. These structures resembled aborted formation of seminiferous tubules. There was no evidence of any zona pellucidae; convenient markers for the presence of primordial (primary) follicles.

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In summary, this animal had gonads that were more testis-like than ovary-like. Therefore it was assumed to be a male pseudohermaphrodite; a partially developed female with male-like gonads.

In rare cases, freemartinism may cause such severe masculinization of the female tract, that it is almost completely male, so there is remote possibility that this animal's phenotype could have been an extreme manifestation of freemartinism.

We were not able to perform karyotyping in this case because live cells are required for karyotyping. Neither unfortunately, were we able to perform FISH (fluorescent in-situ hybridization) for the Y chromosome or male gene sequences such as the SRY gene. The latter was merely due to lack of financial resources. Immunohistochemical staining of the stromal cells in the gonads of this animal would probably have revealed the presence of androgens.

Notes: Male pseudohermaphrodites are far more common that true hermaphrodites. Male pseudohermaphrodites such as this animal, are essentially incompletely masculinized females. One should recall that the default gender for all embryos is female and in the absence of any gonads, a female reproductive tract will develop. In the presence of testes however, Sertoli cells produce inhibin and anti-müllerian hormone, suppressing the female tract (the müllerian/paramesonephric system). Also, androgens from the testes stimulate the formation of the male system (penis, accessory glands etc). The result is a male animal. Any defect that interferes with this process will result in the development of an incompletely converted female-to-male i.e. a pseudohermaphrodite. Because these animals have testes, they are termed male pseudohermaphrodites, named for the type of gonads they possess. They do not possess gonadal tissue from both sexes therefore they are not true hermaphrodites.

Interestingly, the gonadal sex is not always determined by the karyotype in these animals i.e. almost any karyotype can be associated with almost any form of intersex. Also although male pseudohermaphrodites commonly have XX karyotypes with variable SR-y characteristics, any combination of these is possible. Therefore neither FISH nor karyotyping may have revealed what would have been "diagnostically convenient" i.e. An SrY male with an XY karyotype.

True hermaphroditism can be bilateral (an ovotestes on both sides), unilateral (one ovotestis and one gonad of either sex) or lateral (an ovary on one side and a testis on the other). Initially therefore (prior to histological examination) the tentative diagnosis on this case was lateral hermaphroditism. This turned out to be an incorrect assumption.

Apart from freemartins, which can be regarded as true hermaphrodites, other true hermaphrodites are rare (In some extremely rare cases, separate male and female gonads can be found on both side (two testes and two ovaries ~ 4 gonads); a hermaphrodite beluga whale with four such gonads has been reported. De Guise, D. 1994. True Hermaphroditism in a St. Lawrence Beluga Whale (Deiphinapterus leucas) J. Wildlife Diseases. 30:287-290

Finally, it has been shown that feminization of the male tract is possible in mice (Behringer, 1995) when the dam expresses a gene for high concentrations of anti-müllerian hormone. Such a syndrome would not be detected by the  diagnostic tools that we would have used. However, the bovine placenta is less intimate that the murine placenta, so it is unlikely that a large peptide molecule such as AMH could cross the placenta and feminize the tract.

A calf with amelia

Keywords: amelia, bovine, forelimb, chromosome

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A Holstein calf with amelia. The calf was donated and euthanized.

In humans, thalidomide is well known to cause amelia and meromelia (absence of part of a limb) but it has also been associated with genetic abnormalities. Conditions such as Roberts syndrome exist where amelia and cranio-facial anomalies are linked. Little is known about the etiology of amelia in cattle but in at least two cases it has been linked to chromosomal instability and polyploidy. See case and citation Szczerbal, I. 2006. Chromosome Instability in a Calf with Amelia of Thoracic Limbs. Vet. Path. 43: 789-792

Bovine mummified fetus

Keywords: BVD, leptospirosis, chromosome, mummy, mummified, bovine, fetus

A mummified fetus obtained from a slaughter specimen. The images show the fetus in state of autolysis where the anatomy is barely recognizable. Even after washing, the identity of the flipper-like mass seen here was not obvious; it contained no bones. The cervix was closed in this case, plugged with thick cervical mucus. The fetus weighed approximately 5.4kg and was lodged in the left uterine horn. It was estimated that the fetus was approximately 5 months of age at the time of its death. A corpus luteum in the left ovary supported the mummified pregnancy.

The mummy as presented (top) and below, partly extracted:

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The mummy, completely removed from the uterus.

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The causes, incidence and treatment of bovine mummified fetuses are elegantly reviewed by Lefebvre R. C. et al 2009. Retrospective case study of fetal mummification in cows that did not respond to prostaglandin F2α treatment. Can Vet J. 50: 71–76 Causes are numerous; BVD, leptospirosis, genetic Jersey, Guernsey and individuals that have experienced mummification before. Self cure does occur but appears to be rare. Usually luteolytic treatment with prostaglandin is effective but in some cases, even luteolysis, endocervical PGE and estrogens are not curative. In such cases, surgery or even extraction per cervicum must be used.

Probable hamartoma in a Holstein neonate.

Keywords: ovary, bovine, neonate, cyst, mucus

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A female Holstein calf was submitted by RDVM having died approximately one day after it had been born. Signs of acute septicemia at post mortem examination suggested that septicemia as the cause of death. The calf weighed 46 kg

The reproductive tract was particularly interesting: The right ovary had been replaced by a large cyst weighing approximately 287g. This suggested that the cyst contained approximately 280 mL of fluid. This fluid was yellow and transparent, foaming on aspiration suggestion some content of protein. During dissection, the cyst was found to contain two smaller cysts, one of which was lined by hemorrhagic tissue approximately 1 mm thick.

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The entire ovary was retained for histological examination. Histology was examined at the sites marked Cyst 1 and Cyst 2 above. Clicking on the links Cyst 1 and Cyst 3 will open an interactive microscopy system that allows one to examine those samples. This author detected no signs of neoplasia in the wall of the cyst but occasional foci of round cell infiltrations were seen, indicating chronic inflammation due perhaps to tissue necrosis. In the opinion of Dr Donald Schlafer DVM. PhD, ACT, ABVP, this structure is probably a hamartoma, not a granulosa cell tumor. However, a definitive diagnosis was not possible without additional tissue (unavailable). A hamartoma is a focal malformation that resembles a neoplasm. It is however not a tumor, growing at the same rate as the surrounding tissue. It is essentially a disorganized mass of tissue elements normally found in that organ.

On gross examination, the left ovary appeared to be inactive. The ovary and the tip of the uterus adjacent to the ovary was retained for histology. The histology of those samples can be seen by clicking here. The ovary showed frequent nests of the stromal cells that usually surround primary and secondary follicle development. However, using the histology of ovaries of one and three month old calves as reference points, these nest appeared to be more dominant than expected and oocytes were not as frequently seen as expected. In the opinion of Dr Schlafer, this ovary appeared dysplastic, concurring with the author's opinion.

The structure of the caruncles, devoid of glandular development is easy to appreciate. In the cross section of the tip of the horn, the caruncles bulge into the lumen of the uterus. In the inter-caruncular areas, sections of rudimentary glands are visible.

The rest reproductive tract appeared to be normal other than a large accumulation of gelatinous mucus in the vagina cranial to the area of the hymen. There was no persistent hymen i.e. the vaginal lumen was continuous from the vulvar lips to the cervix, yet the mucus was thick enough to be localized to the anterior vagina.

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The caruncles appeared to be particularly well-developed, more so than normal, as did the clitoris. With an absence of follicle activity in the non-cystic ovary (an otherwise potential source of steroids) the collection of mucus in the cranial vagina and development of the caruncles and clitoris suggested that the cyst may have been endocrinologically active. Steroid assay of its fluid content is pending.
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Heifer with an XY karyotype

Keywords: XY, heifer, bovine, infertility, karyotype, Sry

A heifer was examined because she had not shown signs of estrus although she was significantly larger than normal, cycling, age-matched herd mates.

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On transrectal examination, the genital tract was difficult to define but a cervix and small ovaries were detected. The presence of a vagina and cervix excluded the possibility of freemartinism. Cultures of skin fibroblasts and lymphocytes revealed a homogeneous population of X-Y bearing cells i.e. this animal was genetically a male. It was not possible to determine the Sry status of this animal because suitable primers for the Sry sequence were not available to us at that time (2001).

The animal was donated for further study. The tract was smaller than that of a heifer but a uterus with two horns and a body, a cervix and a vagina was present. The ovaries measured approximately 2.5 x 1 x 1 cm but were firm, wrinkled and devoid of any obvious follicles.

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A close up view of the right ovary:

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On histological examination o the ovaries, there was no evidence of any primordial follicles (oocytes) but a mass of swirling fibrous interstitial tissue contained "islands" of cells.

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Examination on high-power did not lead to additional clarification as to the nature of these structures.

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Because of the presence of an intact Müllerian system (the uterus, cervix and cranial vagina) in this animal, it is unlikely that there were Sertoli cell components in the gonads. Sertoli cells are a source of anti Müllerian hormone and inhibin, two closely related hormones that actively suppress the formation of the Müllerian system in the fetus. Therefore it is tempting to suggest that the islands of cells were abortive attempts to form a follicles, in the absence of oocytes.

The split scrotum in a calf

Keywords: scrotum, bovine, split, testis, testes

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A split scrotum in a prepuberal calf. There was a normal-appearing testis present in each half of the scrotum. The significance of this rare finding in cattle is not known. Split scrotums have been described in humans, dogs and goats.

Author credit and copyright: Unknown

Holstein triplets

Keywords: triplets, bovine, cow, pregnancy,hymen

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Triplets from a six-year-old Holstein cow weighing 652 Kg at the time of admission. The cow died at the time of admission due to fatty infiltration of the liver. It was assumed that the cow had been in a state of energy deficiency because she was carrying triplets.

These triplets were conceived during a nonmedicated cycle but the cow had produced twins earlier in her life and was a cotwin herself. There were four corpora lutea in her ovaries.

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Interestingly, in addition to the triplets an amorphous globosis (shown in the top image between the calves) was present, suggesting that it had been conceived from the fourth ovulation. If this had indeed been the case, it probably did not have a male genotype because the three calves were apparently normal, showing no signs of freemartinism.

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The only abnormality in the genital tract of one calf was the presence of a partially persistent hymen. That hymen is shown by the lower probe on the right side of this image. The upper probe merely illustrates that this calf had a normal cervix.

Approximately one month before they would have been born, the weight of the calves and their crown-rump measurements (respectively) were as follows: 26Kg 84cm, 22Kg 78cm and 28Kg 87cm.

Note: Predisposition to twin ovulation is heritable and varies accordingly from ~ 0 to 15%. Presumably, there is a predisposition to multiple ovulations in general. In beef, triplets births account for less than 0.01% of all calvings. Figures for dairy cows are probably similar.

Interestingly, in super ovulated cattle it has been shown that up to 3 fetuses may be present within within a single uterine horn with up to five calves going to term. When third calves were cross-fostered to a dam whose calf had died, survival rates to weaning were 96%, 86% and 69% for singlets, twins and triplets respectively (Echternkamp J. 1992, Anim. Sci. 2007. 85:3239-3248)

Synchronizing follicle growth in cattle; Ovsynch

Keywords: synchronize, bovine, ovsync, cow, estrous, estrus, cycle, mechanism

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This diagram, extrapolated from many sources, shows the mechanism of Ovsynch treatment.

The receptive periods during the estrous cycle when GnRH will cause ovulation  are shown as gray vertical bars. If GnRH is given during any of these periods (about 65% of the duration of a three wave estrous cycle) follicles present at that time will ovulate, causing a drop in inhibin, FSH release, and the start of new wave of follicle growth. It is this wave of of follicle growth that is utilized to provide synchronous ovulations about nine days later.

As mentioned, a synchronous response to the first injection of GnRH occurs in about 65% of cows. Nine days after the first injection of GnRH, some of the non-responding cows will either respond to the injection of prostaglandin and show estrus or they may show estrus spontaneously. In this manner, about 65% of cows will respond to the first injection of GnRH and about 35% of the cows (the non-responders) will be in estrus after the injection of prostaglandin and will respond to to the second injection of GnRH, together with the other cows. Collectively this means that about 85% of all the treated cows could respond to Ovsynch treatment.

These figures assume that all the cattle being treated are actually having estrous cycles. In high producing cows, is seldom the case so the response to Ovsynch treatments may often fall short of these calculations.

Synchronizing follicle growth in cattle.1

Keywords: synchronize, bovine, ovsync, cow

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This diagram, extrapolated from many sources, shows the receptive periods during the estrous cycle when GnRH will cause ovulation (gray vertical bars). If GnRH is given during any of these periods, follicles present at that time will ovulate, causing a drop in inhibin, FSH release, and the start of new wave of follicle growth. It is this wave of of follicle growth that is utilized to provide synchronous ovulations about nine days later.

Seven days after the initial injection of GnRH, an injection of prostaglandin is given to cause luteolysis of the corpora lutea that were formed seven days earlier. Two days after the injection of prostaglandin, another injection of GnRH is given so that the follicles that have grown in the new wave are induced to ovulate. Sometimes cattle are bred at this time; this is called "Cosync" treatment because the second injection and the time the breeding coincide. Alternatively, they can be bred at a fixed time, usually about the morning after the second injection of GnRH (about 16 hours later). This is referred to as "Ovsync" because ovulations are closely grouped around this period of time. Finally, cows may only be selected for breeding if they show heat; hence the name "Selectsync".

In some instances, injections of prostaglandin are given (even if "Ovsync" itself may be used) to increase the chances that cows will be in the receptive periods (gray vertical bars) at the time the first GnRH is given for Ovsync. The economic value of these pre-synchronization ("Presync") treatments is questionable.