Histologic features and results of virus isolation tests of tissues obtained from teat lesions that developed in dairy cattle during winter

Abstract

Objective - To determine microscopic features and involvement of viruses in teat-end lesions (TEL) of dairy cows during winter. Sample Population - Teats with TEL on lactating Holstein cows and from udders of carcasses. Procedure - Tissues obtained from TEL of 10 teats from 7 cows on 2 research farms during the winter of 1994 to 1995 and 13 teats with TEL excised from udders of carcasses at an abattoir during February 1995 were submitted for virus isolation. During the winter of 1995 to 1996, an increased prevalence of TEL was observed in a research herd. After a decrease in ambient temperature, TEL were identified, and a full-thickness section of epidermis was removed from skin surrounding teat orifices. Tissues were examined by use of light and electron transmission microscopy. Results - Viruses were not isolated from TEL tissues. Lesions ranged from mild elevations of the epidermis to thickened oval regions that encircled the teat orifice. The most severe lesions were dark and had thick crusts. Histologically, TEL were composed of thickened regions of epidermis most notably caused by hyperplasia of cells within the stratum spinosum. Excess production of keratinocytes was also evident, and the keratinocyte layer often contained bacteria. Ultrastructurally, squamous cells contained large amounts of keratin, but virions were not detected. Evidence of a viral etiologic agent for TEL was not detected. Clinical Implications - Development of TEL may be associated with decreases in ambient temperature. Numerous bacteria were evident in the keratin of TEL. Lesions and associated bacteria may predispose cows to mastitis.