Relationship between concentration of lingual antimicrobial peptide and somatic cell count in milk of dairy cows

Lingual antimicrobial peptide (LAP) belongs to the β-defensin family in cattle and is found in milk. LAP concentrations increase in milk from mastitic udders; however, the relationship between LAP concentrations and the somatic cell count (SCC) in milk remains to be elucidated in detail. Therefore, the present study was undertaken to investigate the relationship between LAP concentrations and the SCC in bovine milk to assess whether LAP may be used as an indicator of SCC. Milk was collected from 66 udders showing various SCCs. The SCC and LAP concentrations were measured in the milk. A significantly higher LAP concentration was observed in milk having 500–5000 × 103 cells/ml and >5000 × 103 cells/ml SCC groups than in lower SCC groups (<50 × 103 cells/ml and 50–500 × 103 cells/ml). A significantly positive correlation between LAP concentrations and SCCs in milk was observed (r = 0.68). In milk samples with >26 nM of LAP, 92.0% of milk samples had high SCCs (>200 × 103 cells/ml). The concentration of LAP in milk infected with Staphylococcus aureus, Streptococcus bovis, Streptococcus dysgalactiae, and Escherichia coli was significantly higher than that in uninfected milk. These results suggest that the concentration of LAP can be a useful indicator of the SCC in dairy cows.