The umbilical vein and arteries in a bovine fetus

Keywords: bovine, umbilical, cord, artery, liver, vein, falciform

The equine umbilical circulation is discussed elsewhere in LORI and contributes to this entry.

Normally, the major blood vessels in the amnionic portion of umbilical cord of calves i.e. two veins and two arteries (three vessels in foals) snap and close by elastic recoil at the time of birth. Together with normal clotting mechanisms, this affords complete hemostatis.

Even after birth, two umbilical veins can be discerned close to the body wall of a calf using ultrasonography. These veins then fuse after entering the abdomen and drain towards the posterior vena cava through the liver. The single intra-abdominal umbilical vein is seen in figure 1. Unlike umbilical veins, umbilical arteries are not usually visible outside the body using ultrasonography intermediately after calving.

Figure 1: Perihepatic and perivesicular structures in a late gestation bovine fetus. These structures have been emphasized by post-processing coloration. The intra-abdominal umbilical arteries shown here carry de-oxygenated blood back to the placenta and are in that sense, akin to veins. Nevertheless, these arteries, like those in the umbilical cord, have histological features that are consistent with arteries. After birth, the intra-abdominal umbilical arteries are redundant and degenerate to form the round ligaments of the bladder.  The umbilical vein degenerates to form the round ligament of the liver. The membrane between the round ligament, body wall and liver becomes the falciform ligament (< Latin falc, meaning sickle ) in the calf. Image size: 1400 x 746

The urachus of course, degenerates completely in most animals. However, on rare occasions in cattle (but commonly in humans) the urachus may persist as a thin cord or tubule between the cranial aspect on the bladder and the abdominal wall. On rare occasions these remnants may cause intestinal strangulation.

Figure 2: An interesting comparison with figure 1 is seen in this image from Diseases of cattle, sheep and Swine by the French Veterinarian Gustave Moussu (1864-1945). Book copyright dated 1906. No known copyright restrictions. Image size: 1475 x 966

As mentioned, a single umbilical vein perfuses the liver. However, another major blood vessel diverges from the umbilical vein within the liver but does not perfuse the liver. Instead, it drains directly into the posterior vena cava. This vessel is the ductus venosus. Therefore, not all of the blood from the placenta perfuses the liver to exit that organ via the hepatic veins and enter the posterior vena cava. A small proportion, perhaps 30 percent, bypasses the liver through the ductus venosus and enters the posterior vena cava. As the fetal liver matures, progressively less blood bypasses the liver through this vessel. But even after birth, small amounts of umbilical blood may bypasses the liver and flow directly into the posterior vena cava.  In general, no umbilical blood should bypass the liver by 5 to 7 days postpartum When the ductus venosus persists after birth, some blood flows directly from the portal vessels into the posterior vena cava.  Because that portal blood bypasses the liver, it is not detoxified and neither does it carry beneficial nutrients (metabolized of the liver) into the systemic circulation. This is known as a portosystemic shunt. Portosystemic shunts occur in calves but are most common in dogs. They result in poor growth and hepatic encephalopathy.

Selected references:

Baxter, G.M. et al. 1987. Persistent urachal remnant causing intestinal strangulation in a cow. J Am Vet Med Assoc. 191: 555-558.

Reimer, J.M.  et al 1988 Diagnosis and surgical correction of patent ductus venosus in a calf. J Am Vet Med Assn 193: 1539-1541

Watson, E. et al 1994. Ultrasonography of the umbilical structures in clinically normal calves. Am J Vet Res. 1994 Jun;55(6):773-80.

Embryonic/fetal membrane slipping

Keywords: membrane, slip, fetus, embryo, diagnosis, pregnancy, ruminant, bovine, ovine, caprine, staging.

Membrane slip is commonly used to diagnose pregnancy in cattle, especially in dairy cattle where early pregnancy diagnosis is important. Membrane slip manifests itself when gentle pressure is applied to a fold of the uterine wall. If a conceptus is present, its free allantois or allantochorion or even the free chorion itself, slips away from the constricted section of the uterus. This creates a distinct, palpable "click" between the operator's fingers. 

The composite image below shows how a membrane slip is generated. In image A, the uterus is grasped between the thumb and any finger, then the digits are rolled relative to one another until a firm clicking sensation is detected. The operators digits are not moved off the uterus at any time during this operation. Using an opened, pregnant uterus in image B, one can see how the edge of embryonic/fetal membrane (yellow arrows) is pinched gently between the operator's thumb and finger. As these digits are rolled relative to one another (decreasing the interposing angle between the thumb and finger) the membrane escapes the operator's grip (red and yellow arrows in image C) generating the clicking sensation.

Image size: 1024 x 768px.

In several studies, membrane slipping has been shown to be harmless to the conceptus.

As reviewed elsewhere in LORI, during early gestation, the allantois is not yet attached to the chorion. However, these two membranes gradually become inseparable and collectively, are known as the allantochorion or less commonly, the chorioallantois. Therefore in early gestation, it is either the allantois or chorion or allantochorion that is involved in membrane slipping; a fairly trivial point.

Although the production of pregnancy specific proteins, RNA segments and Interferon Tau have been developed for early pregnancy detection in cattle, ultrasonography is currently accepted as the gold standard for comparison of pregnancy diagnostic methods in cattle; it is both highly specific and sensitive after 28 days of gestation and especially valuable for the diagnosis of twins. However, membrane slipping continues to be a valuable diagnostic tool for routine pregnancy diagnosis. Membrane slipping is also a useful tool for the detection of early pregnancy in small ruminants and wild ruminants when laparotomy is performed for any reason. It cannot be used in new world camelids or equids because of the diffuse placental attachment in those animals.

Comment on the use of the word "fetal" in fetal membrane slip, still a widely accepted term in animal science:

It has been stated that the embryonic period in cattle extends from fertilization to the completion of differentiation at about 42 days (Committee on Reproductive Nomenclature, 1972. Recommendations for standardizing bovine reproductive terms. Cornell Vet 62: 216–237). However it is arguable that differentiation continues throughout pregnancy or even postnatal life and therefore, that the distinction between an embryo and fetus is arbitrary. Even in humans, where an embryo makes its sudden and completely artificial transition into fetal life at 8 weeks, this terminology is under review. Therefore, in this author's opinion, it is erroneous to use fetal membrane slip as a general diagnostic term in cattle, especially dairy cattle. This is because fetal membrane slip is most often used as a diagnostic tool before 42 days, when the conceptus is still formally classified as an embryo. This may be a trivial matter (and in the greater scheme of things, probably is) but like the term embryotomy it should probably be discarded in favor of a more global and accurate term. In that light, the author suggests that instead of the term fetal membrane slip, consideration be given instead, to using the term membrane slip throughout pregnancy.

Selected references:

Ioannidis, J. 2016. Circulating miRNA signatures of early pregnancy in cattle. BMC Genomics. 17: 184

Nation, D.P. et al. 2003. Accuracy of bovine pregnancy detection using transrectal ultrasonography at 28 to 35 days after insemination. Australian Vet. J. 81: 63–65

Preeti Rawat et al. 2016. Identification of potential protein biomarkers for early detection of pregnancy in cow urine using 2D DIGE and label free quantitation. Clin Proteomics. 13: 15.

Romano, J.E. 2006. Early pregnancy diagnosis by transrectal ultrasonography in dairy cattle.
Theriogenology. 66:1034–1041

Conjoined twins

Keywords: conjoined, fetus, monster, bovine

Image size: 3110 x 2074 px

The first image shows conjoined Holstein twins. An accurate description of this case would be:  Conjoined, thoraco/omphalocopagus (joined at the thorax and umbilicus), monencephalus (one head) asymmetric (one fetus larger or distinctly different from the other) tetrapus (four feet) twins. Note: [-pus fr. Greek "pous" meaning "foot"].

The breeding date showed that this was a pregnancy approx. 8 months in duration. Yet, the larger of the two fetuses appeared to be about 6.5 months. This suggesting growth retardation of the larger conceptus.

Note: 
Conjoined twins are named according to the section of the body where they are joined. Then the suffix "pagus" (fr. Gk  pagos meaning “fixed”) is added. Parapagus is the most extreme form of conjoining where the notocords (the earlier axial support of the body) develop in close approximation, hence the use of the term  "para" (fr. the same word in Gk  meaning “beside or next to”). Less extreme forms are pygo- (tail), thoraco- , rachi- (fr. Gk  rachis meaning "spine"), omphalo- and ischio- (fr. Gk iskion meaning “hip”). Other terms are added for greater accuracy.

As described in detail elsewhere in LORI, conjoined twins are invariably of the same gender and arise from a late division of a single conceptus, when the primitive streak is already forming. Usually this means that conjoined twins share a single amnion within a single chorion. Unfortunately this interesting phenomenon is seldom recorded in veterinary medicine, probably because the surgeon is preoccupied in delivering the conjoined twins by Cesarean section.  Those who encounter conjoined twins are encouraged to examine and photograph their fetal membranes carefully and to forward those results to this author for possible inclusion in LORI.

Although one would presume that conjoined twins must always delivered by Cesarean section, this is not necessarily so; several cases of vaginal births of live, conjoined twins have been reported in humans and at least one in a grey whale. In quadrupeds like domestic animals, it may be possible for premature conjoined twins to be born per vagina but the author is unaware of natural delivery of conjoined twins at term.

This image below (38 years old!) shows a set of conjoined, thoraco/omphalocopagus twins but unlike those in the first image, these are symmetrical in nature. Read elsewhere in LORI how these twins are usually mirror images of one another, often with situs inversus of the internal organs.

Image size: 1024 x 654 px

The fetuses in the image below could be described as bicephalus and bicaudate, parapagus conjoined twins.

Image size: 1000 x 657 px.

As mentioned in the first paragraph, parapagus is the most extreme form of conjoining where the notocords of each embryo develop in close approximation.

Another entry in LORI illustrates an even more extreme degree of fusion than those shown here: a janusceps (janisceps) fetus.

Macerated bovine fetus

Keywords: bovine, macerated, fetus, surgery, fertility

Bones of a macerated fetus removed by hysterotomy from a seven year old Angus cow.

Image size: 1555 x 794px  Author and holder of copyright: Dr Swanand Sathe. Iowa State University. swansathe@gmail.com

The cow with this pregnancy was presented with a history of anestrus and a chronic vaginal discharge. A diagnosis of fetal maceration and metritis was made. Using hysterotomy via a caudal flank incision, fetal bones and debris were removed. Aggressive post-surgery medical treatment was used and after five months of sexual rest, the cow conceived, produced excellent embryos for embryo transfer and later, became pregnant herself.

Note: Surgical treatment for macerated fetuses by laparotomy is not common. This is because the uterus is small and lies within the confines of the pelvic inlet. Therefore it is difficult to approach through a flank incision. Medical treatment using luteolysis followed by prostaglandin-induced cervical relaxation then manual dilation, has been successful in the short term. However, long term fertility data is scant. The same is true of hysterotomy via colpotomy.

In this case, a surgical approach was indeed attempted and proved to be successful in terms of long term fertility. As the authors of the published case have reported, there was also significant uterine pathology, so the outcome was more favorable than expected. 

Acknowledgements: The author wishes to  thank Dr Robert Youngquist,  Editor, Clinical Theriogenology and owner of copyright to the image, for allowing it to be reproduced in a modified form in LORI. This author is also indebted to Dr Swanand Sathe, the author of the original image and Dr John Herrmann, principle author of the article published in Clinical Theriogenology (see reference).

Reference: 

Herrmann, J.A. and Sathe, S.R. 2014. Reproductive performance of an Angus cow after removal of a macerated fetus via caudal flank laparotomy and hysterotomy. Clinical Theriogenology. 6:41-52.

Bovine placental anatomy

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

Image size: 2000 x 2895px

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):

Image size: 2000 x 1496px

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.

Image size: 1238 x 1172px

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

Image size: 2441 x 1866px

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.

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:

Image size: 2000 x 2730 px

The mummy, completely removed from the uterus.

Image size: 4199 x 2745 px

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.