Several studies have demonstrated an association between impaired innate immunity and metabolic parameters, particularly during the periparturient period. However, to our knowledge, no study has been conducted under field conditions investigating the link between low milk polymorphonuclear neutrophil (PMN) levels and increased disease frequency. In an attempt to address this knowledge gap, this study examined 6209 cows from 20 dairy herds in Lombardy that were enrolled in a monthly individual dairy herd improvement milk testing program. Analyses of milk test record samples (MTR) included somatic cell count (SCC) and differential cell count (DSCC). A third variable, PLCC (polymorphonuclear neutrophil leukocyte cell count), was calculated by multiplying SCC × DSCC, thus representing PMN cells/mL. A database including compulsory records of all antimicrobial treatments applied in each herd was used as a proxy for disease frequency. In total, 58,090 valid MTR and 12,014 antimicrobial treatments (AMT) were considered for this study. Statistical analyses showed a significant association between the prevalence of cows with a low number of milk PMN and the prevalence of AMT. These results allow routine identification of whether the number of cows with low PLCC exceeds an alarm level within a herd. This threshold was calculated using an ROC curve with a cut-off point of 6% for AMT. This threshold was estimated at 2%, providing 78% accuracy in identifying herds at risk of an increasing treatment rate. This study confirms that cellular markers measured within MTR systems are useful in identifying herds at risk of impaired cellular immunity, thus paving the way for further studies assessing herd and cow immune status with routine milk sampling.

In recent years, there have been important regulatory and management changes in livestock farming in Italy and other European countries. The goal of these changes has been to decrease the use of antimicrobials (antimicrobial stewardship). The objective of this observational study was to explore the potential relationship between the decrease in the use of antimicrobials and the rise in the culling of dairy cattle on 210 farms in the Lodi province. Records of antimicrobials used in dairy herds (measured as the daily defined dose animal for Italy—DDDAit) and culling rates were retrieved from the Italian Ministry of Health official databases. These were statistically analyzed to assess the presence of an association between changes in the DDDAit and changes in the culling rates in 2023 and 2024. The results indicated that the DDDAit exhibited minimal fluctuations over the two-year period (3.61% vs. 2.45%). However, there was a notable shift observed in the culling rates, particularly among smaller herds (24.51 vs. 39.27%). The statistical analysis showed a significant correlation between herd size and antimicrobial treatment, with a higher frequency in larger herds. The results of this study indicate that reducing antimicrobial treatments alone may not necessarily result in better animal welfare or herd sustainability, particularly when it is associated with an increase in the culling rate. It also suggests that antimicrobial treatment rates and culling rates derived from a mandatory recording system provide a simple means of verifying the level of herd health management and of assessing the antimicrobial stewardship approach efficacy.

Several studies have demonstrated an association between impaired innate immunity and metabolic parameters, particularly during the periparturient period. However, to our knowledge, no study has been conducted under field conditions investigating the link between low milk polymorphonuclear leukocytes neutrophils cells (PMN) levels and increased disease frequency. In an attempt to address this knowledge gap, this study examined 6,209 cows from 20 dairy herds in Lombardy that are enrolled in a monthly individual dairy herd improvement milk testing program. Analyses of milk test record samples (MTR) included somatic cell count (SCC) and differential cell count (DSCC). A third variable, PLCC, was calculated by multiplying SCC x DSCC, thus representing PMN cells/mL. A database including compulsory records of all antimicrobial treatments applied in each herd was used as a proxy for disease frequency. In total, 58,090 valid MTR and 12,014 antimicrobial treatments (AMT) were considered for this study. Statistical analyses showed a significant association between prevalence of cows with a low number of milk PMN and the prevalence of AMT. These results allow to routinely identify whether the number of cows with low PLCC exceeds an alarm level within a herd. This threshold was calculated using a ROC curve with a cut-off point of 6% for AMT. This threshold was estimated at 2%, providing 78% accuracy in identifying herds at risk of an increasing treatment rate. This study confirms that cellular markers measured within MTR systems, are useful in identifying herds at risk of impaired cellular immunity, thus paving the way to further studies assessing herd and cow immune status with routine milk samplings.