The uterine arteries

Keywords: uterus, artery, middle, arteries, anatomy

During transrectal palpation of the pregnant bovine uterus, it is common to feel for the presence of fremitus in a uterine artery. A video of a windsock, simulating fremitus can be seen here. It shows non-linear, turbulent flow of air through a windsock; the sock is unable to constrain the airflow in a linear, orderly fashion. During pregnancy in ruminants, blood flow to the uterus increases rapidly, exceeding the ability to contain the blood flow in a linear flow. The effect is the same in both cases.

Since antiquity, this artery has been referred to by clinicians as the middle uterine artery, implying that there are several major arteries within the mesometrium. Indeed, this is clearly the case as shown below (A, B & C...perhaps more). However, the image also shows that there is only major uterine artery (UA) from which the smaller arteries emanate. That artery should correctly be referred to as the uterine artery.

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The question arises as to which of these arteries can develop fremitus during pregnancy. Clearly the major artery is capable of doing so. Therefore if there is any doubt as to which artery one is grasping during pregnancy diagnosis, it may be most correct to refer to "fremitus in the uterine artery" rather that "fremitus in the middle uterine artery". Finally, there is clearly potential for the development of an even number of large arteries in the mesometrium, in which case there can be no middle artery. Collectively therefore, the term "middle uterine artery" is probably incorrect in many instances of transrectal palpation. In the absence of clinical evidence to show otherwise, the term "uterine artery" should  be used.

The recto-genital pouch and ovariectomy in heifers

Keywords: recto-genital, spay, ovariectomy, anesthesia, anatomy

The recto-genital pouch of a cow. A ruler has been inserted into the pouch, pulling back its cranial peritoneal reflection. The pouch is perhaps, 5 to 6 cm deep at most. At its most cranial aspect, inside the vagina and below the black arrows, lies the external cervical os. This anatomy is important in a discussion on ovariectomy.

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Feedlot heifers are sometimes ovariectomized to prevent weight loss (through increased activity) and injury from mounting. The cost of the procedure and the lower weight gain and feed conversion in ovariectomized heifers are negative aspects of ovariectomy. Nevertheless, ovariectomized heifers appear to have an improved response to growth implants when compared to intact heifers. (U. Minnesota extension services data). Also, ovariectomized heifers are not considered to be breeding animals, therefore their movement out of TB zones is not restricted in the US.  Consequently, ovariectomy is still an important part of feedlot management.

Ovariectomy is usually performed via colpotomy (a per vagina incision); seldom via flank incision. Commonly, a. Meagher ovary flute, Kimberling-Rupp or Willis (drop) spay instrument is used. It is the tip of Willis drop instrument that is shown in the image below. It is so named because the ovaries are not retrieved, but allowed to drop into the peritoneal cavity. 

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Whichever instrument is used, its tip is passed from through the dorsal wall of the vagina (adjacent to the fornix of the cervix) and into the peritoneal cavity as shown. This means that it penetrates the peritoneum in the cranial portion of the recto-genital pouch. The ovaries are then removed as described for each instrument.

In the author's experience with mares (where ovariectomy is performed for different reasons) the cranial vagina does not appear to be sensitive to cutting but is well-endowed with stretch-pain receptors. Strangely, mares do not respond if a scalpel incision is made in the fornix of the cranial vagina (beyond the cranial extent of caudal epidural anesthesia when used) but stretching and penetration through the peritoneum definitely cause discomfort. In addition, stretching of the mesovarian ligaments and the use of an ecraseur to remove the ovary are both painful. Therefore, flushing of these structures with local anesthetic is required to proceed humanely. Even under general anesthesia in bitches that are being ovariectomized, traction on the ovarian ligaments can cause pain and tachycardia. Ovariectomy in feedlot heifers is usually done in the complete absence of anesthesia. In this author's opinion, humane aspects of ovariectomy in heifers should be addressed more progressively than they are. 

At present, the policy of the American Veterinary Medical Association (AVMA) in this regard is as follows: 

"When ovariectomy is deemed necessary the procedure should be performed using appropriate restraint and aseptic technique. Research leading to new or improved techniques that reduce or eliminate pain and discomfort associated with ovariectomy, or development of viable alternatives to ovariectomy, is encouraged." 

The bovine infundibulum

Keywords: anatomy, bovine, ovary, infundibulum

The complex flower-like appearance of a bovine infundibulum suspended in water. A key to this image appears below it.

The macroscopic complexity of the bovine infundibulum may exceed that the equine infundibulum. The functional significance of this is open to debate. Also remarkable is the sculpted, frilly margin of the mesopsalpinx i.e. the margin of the ovarian bursa. The bright pink appearance of the uterine tube is striking as well.  It is important to note that no color adjustments were used in the processing of this image. It was however photographed with LED lighting at 5000K, perhaps explaining why these colors are so vivid and unexpected.

Image size 1903 x 1352px. Readers are encouraged to enlarged this image to it native size.

Key:

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Bovine pregnancy at 38 days

Keywords: pregnant, cow, amnion, chorion, allantois, bovine, 38 days, pregnancy diagnosis, palpation

A bovine pregnancy of approx 38 days from a Holstein cow that was bred by a bull. The cow died suddenly from a unknown cause.  This tract is shown in another LORI entry in an unopened state.

This image shows early placentome formation with small cotyledons on the fetal side and caruncles of the maternal side. The  outermost membrane of the placenta (the chorion) has been stripped away partially to show the underlying allantois on either side of the amnion. Details of these membrane systems and bovine placentation are discussed and shown in greater detail elsewhere in LORI.

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Interestingly, it was not possible to determine the gender of this fetus with certainty by macroscopic examination of the genital tubercle. Although it was close to the caudal aspect of the umbilical cord indicating that this was probably a male, the base of the tail was also close to the cord, normal for this stage of gestation; not excluding the possibility of a female. Certainly this would not have been possible by transrectal ultrasonography.

General anatomy of the bovine tract

Keywords: bovine, pregnant, tract, cow

This is an illustration of the bovine tract exclusive of its blood supply and mesometrial support. The larger image (2000 x 889 px) below

is supported by this smaller (1148  x 768 px ) keyed image.

Note that these images were obtained by photographing the tracts under water with 5000K LED lighting. This method of suspension reveals structures that are not normally visible with when the tract is held in an air environment. See below (pending). Also, the wavelength of the light used demonstrates colors not usually visible in ambient light. No processing manipulation of colors has been used. For example, the bright pink color of the uterine tube (fallopian tube) is its natural appearance under these conditions.