Somatic cell counts as an indicator of mammary infection in periparturient cows

Abstract

The somatic cell count (SCC) is a screening test for the evaluation of intramammary infection; however, changes in mammary secretion during colostrogenesis can promote a physiological increase in the SCC, potentially reducing its reliability in the diagnosis of mastitis. Therefore, the aim of this study was to evaluate bovine colostrum SCC as an indicative parameter of breast infection in Holstein periparturient cows. A total of 80 samples were harvested from the first milking colostrum of 20 cows and were subjected to manual SCC and bacteriological examination. Bacterial growth was present in 36.62% of the crops; coagulase-negative Staphylococcus (CNS) was the predominant microorganism (76.92%). The median SCC in infected cows (1.8 × 10⁶ cells/mL) was significantly higher than in uninfected cows (0.9 × 10⁶ cells/mL) (p = 0.0451). The sensitivity (100–15%), specificity (100–2.2%), and false positive (100–2.2%) of the SCC decreased gradually when thresholds of 0.2–10.0 × 10⁶ cells/mL were adopted. In contrast, the proportion of false negatives (0–84.6%) revealed an opposite trend. The threshold of greatest concordance between SCC and bacteriological examination was 10.0 × 10⁶ cells/mL; however, the sensitivity rates (15.4%), specificity (2.2%), and false positive (2.2%) were very low. Based on these results, we conclude that SCCs increased prior to the infectious processes of the mammary gland, particularly in the CNS group. However, physiological changes caused by colostrogenesis resulted in poor concordance between the SCC and bacteriological examination of the colostrum.