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."
