A Phenotypic Expression of Homozygous Dwarfism in Beef Cattle

Abstract

A study of head contours of over 60 dwarfs and several hundred normal animals of the Hereford, Angus, and Shorthorn breeds reveals that the outstanding characteristic of the specific type of dwarfism studied is a brachycephalic head with a marked mid-forehead prominence present at birth and persisting throughout life. This type of contour is discontinuous with and does not intergrade into the type of contour of normal homozygotes. Accompanying this anomaly is a misshapen mandible in which there is marked malocclusion of the incisors with the dental pad. Incisors may extend forward to the dental pad from one-half to three and one-half centimeters. These characteristics are also symptoms of thyroid deficiency. Moreover, the stunted growth, heavy breathing, and extreme pot-belly of the dwarfs are manifestations of thyroid deficiency characteristic of hereditary or experimentally induced cretins. These morphological features are in agreement with physiological studies completed in our laboratory being reported in another paper which prove conclusively that dwarfs of this type possess a gross deficiency of the thyrotrophic hormone. Copyright © . .