Mastitis is a frequent and expensive disease in the dairy industry, particularly in its subclinical form. Regular SCC testing and bacterial culture are the tools used to monitor subclinical mastitis. However, SCC is usually only analyzed on a monthly basis as part of DHI testing, and bacterial culture is time consuming and rarely done. The composition of somatic cells changes significantly over the course of an inframammary infection. Milk from healthy udders contains mainly macrophages, whereas milk from actively infected glands has a high proportion of polymorphonuclear neutrophils (PMN). Differential SCC (DSCC) offers the possibility to refine the regular SCC analysis by providing the combined proportion of PMN and lymphocytes. 969 cows from 11 farms were involved in the study, from July to October 2017. Once a month and for 2 consecutive milkings, composite aseptic samples (n = 5052) were collected (hand-strip) before milking, and metered samples (n = 7780) were collected throughout milking (plus one 24h composite metered sample). Aseptic samples were cultured and analyzed by Maldi-ToF for bacterial identification. Metered individual and composite samples were analyzed for regular composition, SCC and DSCC. Average DSCC results did not differ between the 4 mo of sample collection, nor between AM, PM and 24h samples. Major pathogens were found in 2507 samples, minor pathogens were in 467 sanples, and 1296 samples had no growth or healthy bacteria. Mean DSCC values were higher for samples where major pathogens were identified (77.7 ± 13.1%) than samples with minor (62.2 ± 17.5%) or no pathogens (58.2 ± 12.0%). Sensitivity and specificity of SCC and DSCC alone or in combination to detect an intramammary infection (any pathogen) were respectively 69.0% and 77.6% for SCC alone; 71.8% and 75.8% for DSCC alone; and 71.7% and 75.4% when SCC and DSCC were used in combination (P = 0.50). These results suggest DSCC is highly correlated with SCC but may not increase the ability to detect subclinical mastitis during lactation compared with the precision of SCC alone. Further data analysis is required and will be focused on detection of specific individual pathogens rather than non-specific infection.