DSCC put to the test in practice
To test whether a combination of SCC and DSCC indeed gives more valuable information, the test characteristics for identification of IMI, caused by major pathogens, were evaluated in a study reflecting routine DHI conditions for DSCC and SCC, as stand-alone parameters and also their combination. The researchers also evaluated the DSCC and SCC results depending on the presence of IMI caused by specific minor pathogens (i.e., specific non-aureus Staphylococci (NAS) species). The findings were published in the August 2020 edition of Preventive Veterinary Medicine. The study involved eleven dairy farms with a total number of 969 Holstein Friesian cows (lactating and dry) located in the province of Québec, Canada. The mastitis pathogens detected were categorised into major (coli- forms (e.g., Klebsiella spp., Serratia spp.), Escherichia coli, Enterococcus spp., Lactococcus garvieae, Lactococcus lactis, Staphylococcus (S.) aureus, Streptococcus uberis, Streptococcus dysgalactiae), minor (Corynebacterium spp., NAS), and other pathogens (e.g., Aerococcus viridans, Pantoea agglomerans, Trueperella pyogenes). Three different IMI statuses were used, based on a.m., p.m. or 24 h milking.
So, can we actually get better and more accurate results when we use DSCC as an addition to SCC? According to the researchers we can. The data from the study provided clear insights that elevated DSCC results were associated with IMI caused by major pathogens. DSCC in cows with no IMI or IMI by minor or other pathogens, on the other hand, showed low DSCC results. As DSCC is a measure of the total immune cells in the sample, it makes sense that DSCC is higher when the cow has to fight major, or more harmful minor pathogens. The body is recruiting more immune cells than dealing with minor, less pathogenic bacteria. Dr Schwarz: “If you would compare two milk samples that both have a SCC of 100,000 cells/ml you would only have that information and consider both samples the same. However, one sample could have a DSCC of 60% and the other sample could have a DSCC of 80%. The high DSCC of 80% tells us that the immune system is quite active fighting something, whereas the lower DSCC of 60% looks rather normal. Knowing this extra information is valuable in udder health monitoring programmes because undetected and untreated IMI by mastitis pathogens clearly present a risk for spreading IMI in a dairy herd. “We have clear thresholds set for SCC, as in cows with a SCC over 200,000/ml have a high risk to have mastitis or a subclinical IMI. The study further showed that the combination of SCC and DSCC allows to identify more IMI (+ 18%!!!) than SCC alone, which is indeed an important advancement with respect to DHI-based udder health monitoring programmes. A DSCC threshold of 65% in combination with a SCC threshold at 200,000 cells/ml lead to the best test results. We are working on further interpreting the results in day-to-day management of dairy farms”.
600 samples per hour capacity
In the past, cell differentiation was seen as a pure scientific method. You had to isolate the cells from the milk and then further investigate them under a microscope or using non-automated flow-cytometry in connection with antibody staining, which are both time consuming and costly activities. “We want to give the dairy industry an inexpensive, practical, and fast tool to measure DSCC. In 2017 we therefore launched the up to 600-sample per hour high-throughput flow-cytometry-based analyser (Fossomatic™ 7 DC) to measure DSCC routinely and simultaneously to SCC on samples that are collected and sent to laboratories anyway. As DSCC represents the combined proportion of PMN and lymphocytes, proportions of macrophages can be calculated by 100-DSCC. We are convinced about the added value of this technology, because pathogens that cause mastitis are constantly evolving and this is why the industry needs to develop new preventive and treatment measures to better tackle this complex disease. The ability to use DSCC as an addition to SCC shows how we are contributing to better udder health management, less mastitis, better milk quality and better farm profitability”, Dr. Schwarz concludes.