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Incidence and Heritability of Ocular Squamous Cell Tumors in Hereford Cattle¹

Colorado State University, Fort Collins 80523

Abstract

Data on ocular squamous cell tumors were collected annually over a 5-year period at the San Juan Basin Research Center, Hesperus, Colorado. A total of 1,105 examinations were made on 396 cows with 535 lesions observed.

The least-squares means for tumor incidence and number of tumors were 46.5% and .74 tumors. Significant (P<.01) sources of variation for both dependent variables were year, line of sire, sire within line, age of cow and for inbreeding (P<.10 and P<.05, respectively).

Heritability estimates were calculated by the paternal half-sib method using several groupings of data. They ranged from negative values (zero estimates) in younger cows to .20 ± .23 and .59 ± .22, respectively, for tumor incidence and number of tumors.

The most common tumor sites were the lateral (66.7%) and medial (16.5%) corneoscleral junctions. The majority of tumors were diagnosed cytologically as atypical (65.2%). Seventy-six percent of all lesions were less than 10 mm , while 66.9% were classified unequivocal. The distribution of tumors between right (37.9%) and left (35.6%) eyes was approximately equal while 26.4% of the cows with tumors were affected in both eyes.

Twenty-nine cases of squamous cell carcinoma (2.6%) were diagnosed. The occurrence of cancer eye is associated with increased age although not limited to older animals. The mean age of incidence was 7.4 years of age. Highly significant differences in the incidence of ocular squamous cell carcinoma existed among lines ranging from .0% to 5.9%. No factors were identified that would aid in the prediction of whether a small benign tumor will become malignant. A large percentage of small lesions regressed or remained unchanged. Squamous cell carcinomas appeared both suddenly in 1 year and slowly with gradual growth over several years, often progressing from papillomas.

¹ Approved for publication as Scientific Paper 2135 of the Colorado Experiment Station.

² Graduate student and professor, Department of Animal Sciences, and professor, Department of Anatomy, Colorado State University, Fort Collins 80523.