The equine cervical canal
Keywords: cervix, anatomy, equine
Figure 1. An interesting view of the equine cervix, photographed under water to show its anatomical intricacy. Image size:592 x 831px
Figure 2. Another view. Image size:2807 x 4174px
It is fascinating to consider the similarity of this intricacy between species. In that regard, note the complexity of the cervix of the Cow and Pilot whale, also in LORI.
A mare's cervix is similar to its uterus and vagina in that it has both inner circular and outer longitudinal smooth muscle layers. It also contains elastic tissue. The muscle of the cervix is supplied with sympathetic innervation but the function of that innervation is not clear. If it is continuous with the sympathetic innervation of the uterus, speculation suggests that it would have predominantly beta 2 receptors, relaxing the cervix in a sympathetically dominated state; perhaps during copulation. This could facilitate entry of the ejaculate into the uterus.
Unlike the endometrium, the cervix contains no submucosal glands. On histological examination, this feature makes it immediately evident that a cervical biopsy had been taken instead of an endometrial biopsy. Almost always, this is the result of doing a so-called "blind" biopsy where the tip of the biopsy punch is not palpated transrectally during the procedure.
Although the image above shows intricate folding of the cervical mucosa, folding of the mucosa is even more complex than it appears at this magnification. Primary folds divide into secondary and even tertiary folds at a microscopic level.
The epithelium lining the cervical canal is predominantly columnar and not surprisingly, contains goblet cells that secrete mucus for sealing the canal, This mucus also contains IgA and IgG. The mucosa is also made up of ciliated cells, the functions of which are less obvious than those of the goblet cells. Ciliated cells may be important in distributing mucus across the surface of the canal, similar to the function of ciliated cells in the endometrium.
Sampling the external cervical os (instead of the uterine lumen) as part of a breeding soundness examination is potentially misleading because the whole of the vagina, including the cervical os is contaminated with bacterial in many normal mares. In normal mares, neutrophils are also found in the external cervical os.
The equine cervix cannot be grasped, elevated and manipulated as it can in cattle. Therefore, even during the luteal phase in cycling mares when the cervix is firmer than otherwise, it may be difficult to delineate. The cervix is also difficult or impossible to delineate clearly using transrectal ultrasonography.
During the luteal phase, the cervical canal is closed but in most mares, it can easily be dilated for diagnostic procedures. When a mare is bred, the cervix remains patent for several days allowing inflammatory products (contaminated fluid, semen and cytokines) to be discharged. The canal closes as progesterone secretion increases. When pregnancy is recognized, cervical tone become remarkable, even firmer than during the luteal phase in a non-pregnant mare. At 13 or 14 days after ovulation, cervical tone often precedes uterine tone as an early indication of pregnancy.
During estrus the cervix will usually relax but in some mares, especially nulliparous (maiden) mares it can be remarkably firm; the unitiated may not even be able to discern the external cervical os. In these mares, the cervix may protrude from the cranial vagina, rather like a finger pointing caudally at the examiner and some manipulation may be required to artificially inseminate the mare. In a few cases, in multiparous mares, the cervix may be so relaxed as to gape open. In most mares however, the state is intermediate between these two descriptions.
If one is to examine a mare for evidence of cervical tears, it is important to do so during the luteal phase. During estrus, the cervix may be so relaxed that cervical architecture is lost, making the tear difficult to see or feel during per vagina examination.
Although the cervix is tightly closed during pregnancy, it can be dilated manually with caution and patience. Subjectively, pre-treatment with intracervical prostaglandin E2 (Prepidil gel. TM.) may assist one in dilating the cervix. However, even in the absence of prostaglandin treatment, the author and others have removed fetuses from uteruses as late as five months into pregnancy. This would not be possible in cattle.
Reference:
Katila, T. 2012. The equine cervix. Pferdeheilkunde 28: 35-38
Unlike the endometrium, the cervix contains no submucosal glands. On histological examination, this feature makes it immediately evident that a cervical biopsy had been taken instead of an endometrial biopsy. Almost always, this is the result of doing a so-called "blind" biopsy where the tip of the biopsy punch is not palpated transrectally during the procedure.
Although the image above shows intricate folding of the cervical mucosa, folding of the mucosa is even more complex than it appears at this magnification. Primary folds divide into secondary and even tertiary folds at a microscopic level.
The epithelium lining the cervical canal is predominantly columnar and not surprisingly, contains goblet cells that secrete mucus for sealing the canal, This mucus also contains IgA and IgG. The mucosa is also made up of ciliated cells, the functions of which are less obvious than those of the goblet cells. Ciliated cells may be important in distributing mucus across the surface of the canal, similar to the function of ciliated cells in the endometrium.
Sampling the external cervical os (instead of the uterine lumen) as part of a breeding soundness examination is potentially misleading because the whole of the vagina, including the cervical os is contaminated with bacterial in many normal mares. In normal mares, neutrophils are also found in the external cervical os.
The equine cervix cannot be grasped, elevated and manipulated as it can in cattle. Therefore, even during the luteal phase in cycling mares when the cervix is firmer than otherwise, it may be difficult to delineate. The cervix is also difficult or impossible to delineate clearly using transrectal ultrasonography.
During the luteal phase, the cervical canal is closed but in most mares, it can easily be dilated for diagnostic procedures. When a mare is bred, the cervix remains patent for several days allowing inflammatory products (contaminated fluid, semen and cytokines) to be discharged. The canal closes as progesterone secretion increases. When pregnancy is recognized, cervical tone become remarkable, even firmer than during the luteal phase in a non-pregnant mare. At 13 or 14 days after ovulation, cervical tone often precedes uterine tone as an early indication of pregnancy.
During estrus the cervix will usually relax but in some mares, especially nulliparous (maiden) mares it can be remarkably firm; the unitiated may not even be able to discern the external cervical os. In these mares, the cervix may protrude from the cranial vagina, rather like a finger pointing caudally at the examiner and some manipulation may be required to artificially inseminate the mare. In a few cases, in multiparous mares, the cervix may be so relaxed as to gape open. In most mares however, the state is intermediate between these two descriptions.
If one is to examine a mare for evidence of cervical tears, it is important to do so during the luteal phase. During estrus, the cervix may be so relaxed that cervical architecture is lost, making the tear difficult to see or feel during per vagina examination.
Reference:
Katila, T. 2012. The equine cervix. Pferdeheilkunde 28: 35-38
