Reduction of Lactobacillus in the milks of cows with subclinical mastitis.

Clinical and subclinical bovine mastitis are the most frequent diseases encountered on dairy farms worldwide, which cause significant economic loss and veterinary cost. The mastitic disease status is associated with increases in both milk bacterial pathogens and somatic cell count (SCC). Although it is well established that the mastitic pathogens generally correlate with the milk SCC, to our knowledge, the correlation between the probiotic genus, Lactobacillus, and the mastitic causative bacteria and SCC have not been determined previously. Thus, in this study, milk samples from 12 mild and 28 severe subclinical mastitic dairy cows were collected from the same farm. The overall milk bacterial load was quantified with the total plate count method. The Lactobacillus genus and 4 common clinical and subclinical mastitic pathogens (Escherichia coli, Staphylococcus aureus, Streptococcus agalactiae, and Trueperella pyogenes) in the sampled milk were enumerated by quantitative PCR. Mild and severe subclinical mastitic samples were distinctly separated on the principal component analysis score plot generated based on the quantities of these 5 target bacteria, suggesting that clear differences existed in the microbiological composition between the two sample groups. Based on comparison with the pairwise Mann-Whitney test, the mild subclinical mastitic dairy cows had a significantly higher amounts of lactobacilli (P=0.0175), but lower E. coli (P=0.0002), S. aureus (P<0.0001), S. agalactiae (P=0.0001) and T. pyogenes (P=0.0044) quantities, while an opposite trend occurred in the severe subclinical mastitic group. The negative correlation between Lactobacillus and the pathogenic bacteria, as well as the SCC, was confirmed with Spearman correlation analysis. Data generated from the current study may hint to a close relationship between Lactobacillus and the health of bovine udder.