Prolonged gestation in a cow
Keywords: prolonged, gestation, ACTH, cortisol, bovine, cow, pregnancy, adrenalNormal gestation is approximately 280 days for cattle. This heifer calf was delivered by cesarean section at approximately 317 days of gestation. This was the second pregnancy for this cow, her previous pregnancy having been normal. The calf weighed 46.5 kg, within the normal range for Holstein neonates.
Pregnancy had been diagnosed by ultrasonography at 30 days, 50 days and 102 days of gestation. Examination at approximately 315 days using per rectum ultrasound revealed a viable calf of approximately normal size. After delivery by cesarean section, the calf attempted to breath but because of obvious abnormalities, it was euthanized using pentobarbital.
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Post-mortem examination showed a prolapse of cerebral tissue through a central orifice in the frontal bone, barely visible between the ears in the image above.
The image below shows the defect in the frontal bones and the prolapsed portion of the cerebrum:
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Most of the cerebral hemispheres appeared to be missing. There was slight asymmetry in the face and both eyes were present but the optic nerve appeared to have no connection to the optic chiasma. There was evidence of hydrocephalus. There was also a severe cleft palate.
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A longitudinal section of the brain after formalin fixation confirmed the presence of severe hydrocephalus in all the ventricles and severe hypoplasia of the cerebellum and cerebral hemispheres. The brain and adrenals of a control calf were available for comparison.
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The longitudinal section clearly demonstrated meningeocele/encephalocele (outlined in yellow here). Histology showed that it contained a large amount of fibrous tissue, some neuronal tissue and some epithelial lined cavernous sinuses.
As seen in the inset, the eyes themselves were grossly normally formed but as mentioned, the optic nerve did not appear to connect to the optic chiasma. The adenohypophysis in the affected calf was distorted and partially absent.
The adrenal glands were approximately 25% of the size of the adrenal glands on a normal calf and on gross examination, when compares with the cross sections of the normal adrenals, the adrenal and cortex appeared to be equally represented in proportions in both the normal and abnormal calf but was far smaller in the calf with prolonged gestation. Histology showed that adrenal gland had all three critical layers present i.e. the zona glomerulosa, zona fasiculata (where cortisol is produced) and zona reticularis.
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Collectively, these findings suggest a quantitative lack of the ACTH-adrenal cortical resources, not an absolute absence. This deficiency probably led to adrenal hypoplasia with consequently prolonged gestation.
