Evisceration during late gestation

Keywords: ovine, gestation, late, accident, pregnancy, sheep

The image below shows a Texel ewe, estimated to be ~135 days post breeding. This animal was found dead in the pasture with no prior signs of debility. The intestines had eviscerated through a tear in the dorsal vagina.

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This ewe was one of six that died suddenly during late gestation. In each of three cases examined by the author, there was a single rupture in the dorsal wall of the vagina, several centimeters caudal to the cervix. Intestines had eviscerated through the tear. In the six cases reported by the farmer, the pregnancies were advanced, approximately 135 to 145 days. The fetuses were twins in all cases and all appeared to be normal. 

The image below shows the location and nature of the rupture and evisceration.

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The following image shows one of the fetal lambs lying in situ, in the left uterine horn.

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This condition is very poorly documented in the literature, it's etiology unknown. Sporadic cases have been reported in the United Kingdom. Characteristically, all ewes eviscerated their intestines through a single tear in the dorsal vaginal wall. Most ewes were found dead, others euthanized. In one case, a failed surgical repair was recorded.

As one practitioner described to the author: "In one case, the shepherd was present and the ewe was standing and not straining when all of a sudden intestines began to pour from the vagina."

Affected ewes show neither vaginal prolapse nor straining prior to evisceration. The incidence may be as high as 5 per cent in some flocks. It has been associated with excessive body condition and feeding of concentrates but some ewes are in poor condition when this occurs. Interestingly, it has not been reported in primiparous ewes. Therefore, one is left wondering if the condition may be associated with previous lambing injuries. Perhaps tearing is precipitated by abdominal pressure increase due to rapid fetal growth, multiple fetuses and distended abdomens after high feed intake.

There is no evidence that sadism is involved in this condition.

Selected references:

Knottenbelt, D.C. 1988. Vaginal rupture associated with herniation of abdominal viscera in pregnant ewes. Vet. Record  122:453-456

Scott, P.R. 2015. Sheep Medicine 2nd Edition. pg 45 ISBN-10: 1498700144 ISBN-13: 978-1498700146

Term uterus and maintenance of pregnancy

Keywords: ovine, sheep, placenta, corpus luteum endocrinology, pregnancy

An illustration of a term uterus and the ovaries.  Although this was a triplet pregnancy, the ovaries were very small (arrows) and contained corpora lutea that were significantly smaller than those in cycling ewes. They appeared to be in a state of regression similar to that shown on the lower left inset, a CL from another term ovine pregnancy.

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In ewes, the corpora lutea are only essential for the maintenance of pregnancy in the first third of a 145 to 150 gestation. After about 60 days (with some variance) neither ovariectomy nor luteolyic treatment with prostaglandins will cause abortion. This is because pregnancy is maintained by the placenta. This situation is distinctly different to that in goats where luteal tissue is essential throughout pregnancy.

With single, twin and triplet lambs in one study, neither gestation length, birth weights nor incidence of dystocia were affected by ovariectomy at 70 days of gestation. The lack of dystocia is not surprising, because ovine corpora lutea are not essential sources of relaxin during pregnancy (as they are in pigs); that role falls to the placenta in sheep.

Although corpora lutea are present at the end of gestation and actively contribute to serum progesterone concentrations,  the essential role of luteal tissue in late gestation remains an enigma.

References:

Al-Gubory,K.H. et al 1999. Effects of luteectomy on the maintenance of pregnancy, circulating progesterone concentrations and lambing performance in sheep. Reprod.Fert.Devel. 11:317 - 322 

Bryant. G and Chamley, W.A. 1976 Plasma relaxin and prolactin immunoactivities in pregnancy and at parturition in the ewe. J. Reprod Fert. 48:201-204

Vaginal tear in a ewe; post prolapse

Keywords: ovine, ewe, sheep, prolapse, vagina, retainer, rupture, pregnancy

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Sequel to the use of a retaining device (upper left in the image) used to keep vaginal mucosa in-situ after returning it to the pelvis. The inset image shows the pregnant uterus within the abdomen.

Below; the location and size of the tear in the vagina:

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Plastic devices  are often used to retain vaginal mucosa in the vaginal lumen after late gestation vaginal prolapse. Pressure from the cranial edge of the device will occasionally cause pressure necrosis of the cranial vaginal, allowing evisceration to occur. Death follows rapidly.

To prevent this problem, this author uses epidural anesthesia followed by a Buhner-type closure. Farmers who cannot avail themselves of this treatment and are forced to use these devices, should probably thicken the cranial edge of the device by whatever means possible. Alternatively, special "prolapse trusses" (commercially available) can be used.

Ovine pregnancy at 25 days

Keywords:  ewe, sheep, pregnancy, embryo, membranes, ovine

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A labeled image of an ovine embryo about 25 days old. The author acknowledges the help of Dr. Glenda Wright (Embryologist; Atlantic veterinary college) in accurately documenting the structures within the embryo.

Placentation and ovulation in a ewe

Keywords: ovine, placenta, pregnancy, melanin

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An ovine uterus that had contained a 25 day twin pregnancy. Note the melanin pigment in the caruncles; a normal finding in many sheep. Also note the early formation of caruncular attachment even though cotyledons were not yet macroscopically visible on the chorion of the fetuses. Of further interest is the fact that small pits are visible (arrow) on the caruncles; these will develop further to become deep and concave, enveloping the cotyledons. This is similar to the situation in goats but is unlike that in cattle where the cotyledons cover the caruncles instead.

There are two corpora luteal in the right ovary, showing that twin ovulation have occurred. Twin ovulations are very common in ewes, and triple ovulations are not uncommon. The presence of a fecundity gene in Baroola ewes makes multiple ovulations very common indeed. The author is aware of one case in a Dorper ewe where seven lambs were born to a single  ewe that had not been pharmacologically superovulated.