samples were tested for presence of mastitis pathogens using bacteriological culture. The final data set comprised of 310 cows of which 64 were in- fected with major pathogens such as Staphylococcus aureus, Streptococcus uberis, Streptococcus dysgalactiae, and E. coli, 149 were infected with minor pathogens such as non-aureus


Table 1- Number of samples and number of mastitis cases caused by major pathogens for different exemplarily chosen SCC and DSCC ranges.


SCC (×1,000 cells/mL) DSCC (%) <50,000 - 50,000–200,000 ≤50 50,000–200,000 50–70 50,000–200,000 >70 >200,000 ≤50 >200,000 50–70 >200,000 >70 1 All data available, n = 310, 2


All samples1 n


91 35 67 23 16 39 39


Mastitis caused by major pathogens n %2 12.1 14.3 17.9 26.1 18.8 30.8 38.5


%


29.4 11.3 17.9 26.1 5.2


12.6 12.6


Percentage of all samples in the respective SCC and DSCC range


11 5


12 6 3


12 15


staphylococci and Corynebacterium sp., and 97 were uninfect- ed. SCC results varied widely from 9,000 to 6,925,000 cells/mL and DSCC results were found in a wide range from 0 to 89.5%. DSCC results indicated a particularly broad variation in the SCC range below 400,000 cells/mL and were found to be generally elevated in samples with higher SCC (Figure 1). Given that a de- fined volume of milk is analysed during the simultaneous measurement of SCC and DSCC, the number of cells available to determine DSCC depends on the total number of cells avail- able per mL of milk. In this context, DSCC cannot be deter- mined reliably in samples with SCC <50,000 cells/mL because they are outside the performance range. Thus, the instrument sets DSCC results to 0% in such samples – however, we have set them to 45% in our study meaning a predominance of mac- rophages is indicated. Nevertheless, an interesting finding of our study was that the majority (45 out of 65, meaning 70%) of cows with mastitis caused by major pathogens revealed DSCC results of >50% regardless of the SCC result (Figure 1, Table 1). Considering SCC as well (Table 1), it becomes evident that the prevalence of major pathogen infections increases within SCC ranges as DSCC results increase. For example, the prevalence of major


Table 2- Results (%) for sensitivity (Se), specificity (Sp), positive predictive value (PPV), and negative predictive value (NPV) for detection of mastitis caused by major pathogens.


Item


DHI samples SCC (x1,000 cells/mL)


DSCC (%) Cut-off(s)


100 200 50 60 70


SCC (x1,000 cells/mL) and DSCC (%) 100,000; 50 100,000; 60 100,000; 70 200,000; 50 200,000; 60 200,000; 70


Hand-stripped samples SCC (x1,000 cells/mL)


DSCC (%)


100 200 50 60 70


SCC (x1,000 cells/mL) and DSCC (%) 100,000; 50 100,000; 60 100,000; 70 200,000; 50 200,000; 60 200,000; 70


30 ▶ COW HEALTH | AUGUST 2020 Correctly identified, n (%) with mastitis without mastitis


42 (65.63) 30 (46.88) 43 (67.19) 37 (57.81) 20 (31.25) 50 (78.13) 46 (71.88) 45 (70.31) 47 (73.44) 42 (65.63) 35 (54.69)


43 (67.19) 30 (46.88) 35 (54.69) 22 (34.38) 7 (10.94) 49 (76.56) 47 (73.44) 45 (70.31) 44 (68.75) 38 (59.38) 33 (51.56)


142 (50.81) 182 (73.98) 120 (48.78) 151 (61.38) 203 (82.52) 92 (37.40) 104 (42.28) 119 (48.57) 109 (44.31) 134 (54.47) 164 (66.94)


129 (52.44) 172 (69.92) 138 (56.10) 184 (74.80) 224 (91.06) 101 (41.87) 117 (47.56) 125 (51.63) 116 (48.98) 146 (59.59) 168 (68.29)


65.63 50.81 48.78 25.77 25.44 85.03


46.88 73.98 31.91 84.26 67.19


85.11


57.81 61.38 28.03 84.83 31.25 82.52 31.75 82.19 78.13 71.88 70.31 73.44 65.63 54.69


37.40 42.28 48.57 44.31 54.47 66.94


67.19 52.44 56.10


24.51 24.47 26.32 25.54 27.27 30.17


26.88 24.48


86.79 85.25 86.23 86.51 85.90 84.97


86.00


46.88 69.92 28.85 83.50 54.69


82.63


34.38 74.80 26.19 81.42 10.94 91.06 24.14 79.72 76.56 73.44 70.31 68.75 59.38 51.56


41.87 47.56 51.63 48.98 59.59 68.29


24.74 26.70 27.44 25.60 27.74 29.73


85.83 87.31 86.99 85.11 84.88 84.42


Se Sp PPV NPV


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