Diagnosing intramammary infections: Comparison of multiple versus single quarter milk samples for the identification of intramammary infections in lactating dairy cows

Abstract

The objective was to examine the potential benefits of using different combinations of multiple quarter milk samples compared with a single sample for diagnosing intramammary infections (IMI) in dairy cattle. Data used in the analyses were derived from 7,076 samples from 667 quarters in 176 cows in 8 herds in 4 locations (Minnesota/Wisconsin, n=4; Prince Edward Island, n=2; Ontario, n=1; New York, n=1). Duplicate quarter milk samples were collected at morning milking for 5 consecutive days. Cows were evenly distributed between early postparturient and mid- to late-lactation cows. All samples were frozen for shipping and storage, thawed once, and cultured in university laboratories using standardized procedures consistent with National Mastitis Council guidelines. The presence of specific pathogens was confirmed and identified using the API identification system (bioMerieux, Marcy l'Etoile, France) in each laboratory. A previously developed gold standard was applied to the first sample from d 1, 3, and 5 to classify infected quarters. The data were analyzed separately for coagulase-negative staphylococci (CNS) and Streptococcus spp. Various combinations of test results from d 2 and 4 were used in the test evaluation. These consisted of single samples (n=4), 2 sets of duplicate samples (2 samples collected on the same day), 2 sets of consecutive samples (2 samples collected 2 d apart), and 2 sets of triplicate samples (2 samples on the same day and a third sample 2 d apart). Series interpretation of duplicate or consecutive samples (i.e., positive=same pathogen isolated from both samples) resulted in the highest specificity (Sp; CNS Sp=92.1-98.1%; Streptococcus spp. Sp=98.7-99.6%), but lowest sensitivity (Se; CNS Se=41.9-53.3%; Streptococcus spp. Se=7.7-22.2%). Parallel interpretation of duplicate or consecutive samples (i.e., positive=pathogen isolated from either) resulted in the highest Se (CNS Se=70.8-80.6%; Streptococcus spp. Se=31.6-48.1%), but lowest Sp (CNS Sp=72.0-77.3%; Streptococcus spp. Sp=89.5-93.3%). The difference in estimates between single and duplicate samples was larger than between single and consecutive samples. Overall, triplicate samples provided the best combination of Se and Sp, but compared with a single sample, provided only a modest gain in Sp and little or no gain in Se.

Evaluation of minor pathogen intramammary infection, susceptibility parameters, and somatic cell counts on the development of new intramammary infections with major mastitis pathogens

“…In this analysis, a stricter definition for IMI caused by CNS was used to maximize specificity of exposure. Single samples were used; previous studies have shown that single samples are often in agreement for contagious organisms (Erskine and Eberhart, 1988) and that the Se of a single sample is better than that of duplicate samples interpreted in series and comparable to that of triplicate samples with only a marginal loss in specificity (Dohoo et al, 2011a).…”

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

“…Thus, the use of composite, single, duplicate or triplicate milk samples can affect the predictive values of microbiological culture (Dohoo et al 2011a, 2011b, Reyher & Dohoo 2011, which is the most expensive component of diagnosing IMI. Then, in an attempt to minimize costs, a relevant question is whether composite milk sampling, or at least individual quarter milk sampling, would be useful for detecting culture-positive milk samples.…”

“…Mastitis refers to inflammation within the udder but not necessarily infection; however, mastitis is usually caused by a bacterial infection (Pyörälä 2003, Dohoo et al 2011a, Dohoo et al 2011b, Reyher & Dohoo 2011, Oliveira et al 2013. Given the central role of intramammary infections (IMIs) in bovine mastitis, high-quality information on the test characteristics of the procedures used to identify infected quarters is required (Dohoo et al 2011a, 2011b, Reyher & Dohoo 2011.…”

“…Information considered in the guidelines for diagnosing mastitis include both results of microbiological culture and measurements of inflammation, in addition to discussion regarding the number of samples that should be tested to maximize sensitivity and specificity parameters (Dohoo et al 2011a). Thus, the use of composite, single, duplicate or triplicate milk samples can affect the predictive values of microbiological culture (Dohoo et al 2011a, 2011b, Reyher & Dohoo 2011, which is the most expensive component of diagnosing IMI.…”

Subclinical intramammary infection does not affect bovine milk ethanol stability

“…Mammary quarters were considered to have subclinical mastitis when milk samples had isolation of > 10 colonies (1,000 cfu/mL) of minor pathogens (Corynebacterium spp. or coagulase-negative staphylococci, CNS); > 3 colonies (300 cfu/mL) of environmental pathogens (environmental streptococci or Gram-negative); ≥ 1 colony (100 cfu/mL) of contagious pathogens (Staphylococcus aureus or Streptococcus agalactiae) or other pathogens as described by (DOHOO et al, 2011a(DOHOO et al, , 2011b. Coagulase-positive staphylococci (CPS), Enterococcus spp.…”