Prolonged gestation in a cow
Keywords: prolonged, gestation, bovine, ACTH, pituitary, skull, eyes, calf, ultrasound, ultrasonographyThe dam of this calf was determined to be pregnant by transrectal palpation, 45 days after breeding. When she had not calved after 10 months, the breeding records were questioned.
Shortly before calving, this pregnancy was examined by transrectal ultrasonography. At that time the amniotic fluid appeared to be cloudy and fremitus was absent. The udder had enlarged in preparation for calving.
Fifteen months after breeding, the pregnancy terminated spontaneously but assistance was required at calving. The attending clinician was unable to touch the calf and initially presumed that it had been aborted in the field. A plank was then used to elevate the cow’s abdomen. This enabled the delivery of a dead 55 kg male calf; in posterior longitudinal presentation. Although the birth was spontaneous, it is doubtful if the calf would have been born without assistance.
The placenta was retained and was unavailable for examination.
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Postmortem showed many fetal defects including the absence of grossly visible contents of the sella turcica i.e. the pituitary gland appeared to be absent. See white ring in image above.
There was micro-ophthalmia, with the eyes only developing subcutaneously. See yellow ring in image above. A well-developed tentorium ossi separated the cerebellum and cerebrum completely and there was only a single cerebral hemisphere with absence of the development of sulci. The cerebral hemisphere was about 20% the size of that of a control neonatal calf. As shown above, there was a complete cleft palate and (below) significant facial-cranial twisting was evident.
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The incisor teeth (see above) had only erupted partially; unusual because they have usually a ruptured completely birth. The thyroid gland was subjectively smaller than that of a normal neonate but the adrenal glands were normal in size compared to those of the aforementioned control calf. The testicles of the calf were not examined.
In general, the cause of prolonged gestation is presumed be due to malfunction or absence of ACTH secreting cells (acidophils) in the adenohypophysis of the pituitary gland. This calf did not appear to have the pituitary gland, consistent with that theory. However, the normal sizes of the adrenal glands were not consistent with that finding suggesting some other source of ACTH. This also suggested that the problem elsewhere in the cascade of hormonal events leading to parturition. Also, total absence of the adenohypophysis was not consistent with the apparently normal growth of the calf because growth hormone-releasing hormone would not have been produced in this calf and growth hormone does not cross the bovine placenta. In combination, these findings suggest an alternate source of ACTH and growth hormone-releasing hormone; perhaps diffuse cells in the area of the sella turcica. The calf was in a fairly advanced state of autolysis when examined therefore some adenohypophyseal tissue may have be present but not visible.
