Previous studies have investigated the peptidomic changes occurring in cow milk during mastitis; however, these focused mainly on clinical mastitis, either spontaneous (Mansor et al., 2013) or induced by experimental infection (Thomas et al., 2016). Mansor and coworkers were the first to use mass spectrometry to demonstrate that several peptides found increased in milk from cows with clinical S. aureus or E. coli mastitis were mainly derived from aS1- and b-casein. In that study, 48 peptides were significantly different between the milks of healthy and mastitic cows. Non-mastitic samples were confirmed to be non-mastitic by having SCC <100,000 cells/mL (Mansor et al., 2013). Thomas and coworkers expanded the peptidomic repertoire in a study evaluating the kinetics of experimental S. uberis infection, and found signature peptides with potential as mastitis markers (Thomas et al., 2016). Only one study evaluated the milk peptidome in subclinical mastitis (Guerrero et al., 2015) demonstrating that even subclinical infections can cause significant increases in the total number of released peptides when compared to uninfected milk. However, neither the IMI agents nor the somatic cell counts were reported. With the aim of understanding high abundance protein and peptidomic changes due to subclinical CNS mastitis, to identify signature peptides with potential for subclinical mastitis detection, and to compare the proteomic and peptidomic findings with those reported in clinical mastitis, we investigated the influence of CNS IMI on high abundance milk proteins by SDS-PAGE and densitometric analysis, followed by a detailed characterization of the milk peptidome by means of high-performance liquid chromatography/tandem mass spectrometry and bioinformatic analysis.