Somatic cell count and mastitis pathogen detection in composite and single or duplicate quarter milk samples

Abstract

The most acceptable criteria for diagnosing bovine intramammary infections include results of bacteriological culture and measures of inflammation. Therefore, information on the diagnostic characteristics of the procedures used to identify infected quarters is required. Thus, this study was designed to evaluate a set of criteria to classify the infectious status of an udder at the quarter (single and duplicate milk samples) and cow (composite milk sample) levels, and to compare the infectious status with somatic cell counts (SCCs) of the samples. Here, the SCC thresholds determined by receiver operating characteristic curve analysis had a higher Youden index using mammary quarter duplicate milk samples as the gold standard for testing compared with single quarter and composite milk samples, especially for samples for which at least one of the duplicates was microbiologically positive, regardless of the mastitis pathogen isolated. The kappa coefficient for bacteriological results of the single quarter milk samples (single S1 and S2) was 0.85+0.019, indicating that single quarter milk sampling can be useful in mastitis control programs. Therefore, the use of composite milk samples to detect mastitis pathogens may be limited to the detection of major pathogens, given their predictive values. Thus, our findings suggest that the milk SCCs and microbiological examinations, although regarded as the most reliable indicators of ongoing mastitis, should be used in an integrated manner in mastitis control programs. Furthermore, the accuracy of single, duplicate and composite microbiological analyses to diagnosis mastitis should be considered for its implications in mastitis control strategies.INDEX TERMS: Somatic cell count, mastitis, intramammary infection, sensitivity, specificity, udder health status, dairy cow.

Diagnosing mastitis in early lactation: use of Somaticell®, California mastitis test and somatic cell count

“…On the other hand, the prevalences of contagious pathogens (e.g. S. aureus, S. agalactiae, S. chromogenes, S. epidermidis and C. bovis) were relatively low, in comparison with other studies in Brazil (Souza et al 2009;Oliveira et al 2011;Souza et al 2016). A positive correlation was observed between the methods for evaluating milk cellularity and the mononuclear and polymorphonuclear leukocyte counts.…”

“…The milk sample was considered positive when !3 colonies grew, with the exception of samples that were positive for either Staphylococcus aureus or Streptococcus agalactiae, which were considered positive with growth of !1 colony (Piepers and De Vliegher 2009;Souza et al 2016). …”

“…Microbiological examination of milk is considered to be the standard method for diagnosing bovine mastitis, despite its limitations such as the time needed for culturing and the costs (Della Souza et al 2016). However, during the inflammatory process, there is significant migration of leukocytes to the area of inflammation.…”

“…Somatic cell counting is a quantitative method for diagnosing mastitis, in which the different types of cells present in milk are enumerated (Souza et al 2016). The California Mastitis Test (CMT) is an easy-toperform, low-cost, fast test that can be performed on the farm, which despite its subjectivity is widely used during milking for diagnosing subclinical mastitis (Della Mira et al 2013).…”

“…Somaticell V R is a quantitative evaluation method, similar to the Wisconsin Mastitis Test, and was developed with the intention of reaching results similar to those of the SCC, but with the advantage that it can be used in the field (Rodrigues et al 2009). SCC cut-off values for diagnosing bovine mastitis have been established at between 100,000 and 272,000 cells mL À1 (Schepers et al 1997;Schukken et al 2003;Bansal et al 2005;Souza et al 2016). However, the cellularity of milk during the immediate postpartum period is high, even in uninfected mammary quarters ).…”