Effect of Teat Hyperkeratosis on Somatic Cell Counts of Dairy Cows

In one study, milk samples from individual mammary quarters (n = 4,148) in seven spring-calving dairy herds in Ireland were collected on two occasions during lactation to measure somatic cell counts (SCCs). All quarters were scored (0 to 4) for teat-end hyperkeratosis to establish a correlation between this score and SCC. In a second study, a herd of 56 autumn-calving Holstein/Friesian dairy cows were milked throughout a complete lactation, and teats on the right side of the body were disinfected after milking by submersion in chlorhexidine solution, whereas teats on the left side of the body were not disinfected. Milk samples were collected from individual quarters to measure SCCs, and the degree of hyperkeratosis was scored at intervals using a scale of 0 to 4 during the lactation. In Study 1, 46% of the teats were given a score of 1 (slight smooth ring of keratin) and 39% were scored 2 (moderately raised, smooth ring). Less than 0.5% of the teats were given a score of 4 (severe broken ring of keratin). There were no differences in SCCs among any hyperkeratosis scores. In Study 2, the mean SCC was significantly (P < .01) lower and the mean hyperkeratosis score was sigIntern J Appl Res Vet Med • Vol. 2, No. 2, 2004 Vol. 2, No. 2, 2004 • Intern J Appl Res Vet Med 116 studies. A simplified scoring method is commonly used for routine evaluation of teat conditions such as teat hyperkeratosis. Hyperkeratosis is a term used to describe a thickened smooth keratin ring or extending fronds of keratin around the teat orifice. The condition has been observed in hand-milked and beef cows, and it is commonly observed in dairy cows. Some studies have suggested that the degree of hyperkeratosis increases as milk yield increases or with longer times on milking machines. Mein and coworkers concluded that the major factors affecting hyperkeratosis are long, pointed teats, slow milking, high-producing cows, stage of lactation, parity, weather conditions, chemical irritation, and cluster removal time. Little or no correlation has been shown between teat orifice hyperkeratosis and intramammary infection. Most studies have calculated correlations using scores from all teat ends and do not allow for individual teat classification. When consideration was given to individual classification of teat ends for the present studies, it was concluded that teats classified with mild or moderate levels of hyperkeratosis did not appear to increase the risk of intramammary infection in lactating dairy cows. However, a greater degree of hyperkeratosis and roughness did increase the probability of new infection. Damage to the teat end allows colonization by pathogenic organisms and reduces the defense mechanism of the teat canal. Biopsies revealed that 50% of hyperkeratotic teat ends contained gram-positive bacterial colonization in the stratum corneum. Colonization of the teat end with bacteria may be greater in the absence of post-milking disinfectant application. Increased colonization in association with a high hyperkeratosis score may increase the risk of mastitis. The present studies were conducted in milking dairy herds in Ireland to examine the effects of hyperkeratosis on somatic cell counts (SCCs) as well as to determine the effects of disinfecting teats on the presence of pathogens. MATERIALS AND METHODS