GENETIC-STUDY OF EYE CANCER IN CATTLE

Heritabilities, phenotypic, and genetic correlations of lid and corneoscleral pigment and eye lesions associated with "cancer eye" were investigated in 2,831 Herefords from 34 herds in 21 states and one Canadian province. The results indicated that lid and corneoscleral pigment were heritable and genetically correlated. Corneoscleral pigment had a direct protective effect on lesions developing at the corneoscleral junction. Corneoscleral pigment and lesion development were apparently not genetically related, and lesion development was not heritable. These findings lead to the general conclusion that the genetic effect on pigment determines to a large extent the degree to which the eye is susceptible to some carcinogenic agent. The ultraviolet light component of sunlight is the most plausible carcinogenic agent that affects the eye. A genetic-environmental interaction is indicated, whereby an increasing amount of pigment lessens both susceptibility and the probability of lesion development, but whether lesions develop in the absence of pigment depends to a large extent on the amount of ultraviolet light to which the eye is exposed. The findings further indicate that the disease is controllable by selective breeding for increased amounts of lid pigment, which should lead to a correlated increase in lid and corneoscleral pigment and a decrease in lesions.