Holoprosencephaly in a bovine calf.

Holoprosencephaly, a rare brain malformation previously unreported in the bovine species, was observed in a female Hereford calf. The malformation was characterized by lack of the longitudinal cerebral fissure and the falx cerebri with fusion of the cerebral hemispheres and a single hydrocephalically dilated lateral ventricle, absence of olfactory bulbs and nerves, corpus callosum and septum pellucidum, and heterotopia. The face was flat. There were mild ocular hypotelorism and severe microphthalmia. The morphological features of this bovine case were compared to those of human infants, and various possible etiologic factors and pathogenesis were discussed.