Microbial diversity analysis of subclinical mastitis in dairy cattle in Northeast China

The microbial diversity of a pooled milk sample (H) from healthy dairy cows in the Daqing region of Heilongjing Province in northeastern China was compared to that of four pooled milk samples (M1-M4) from dairy cows from the same area previously diagnosed with subclinical mastitis, based on the California mastitis test, using pyrosequencing of the metagenomic 16S ribosomal RNA genes. A total of 22 759 valid sequences were obtained from the five pooled milk samples, and the average length of a valid sequence was 484 bp. The composition of the bacterial communities of the M1, M2, M3, and M4 samples was significantly different from that of the H sample. The bacterial diversity of the M1 sample was highly similar to that of M2 sample; the bacterial diversity of the M3 sample was highly similar to that of M4 sample. The Streptococcus and Staphylococcus spp. were highly prevalent in the M1, M2, and M4 samples, and Pseudomonas spp. were highly prevalent in the M1, M2, and M3 samples. The levels of Acinetobacter, Lactococcus, and Flavobacteriaceae spp. in the M1, M2, M3, and M4 samples were lower than those of the H sample, which represents potential risk factors for subclinical mastitis. Our findings provide valuable information relevant to the prevention and treatment of subclinical mastitis in dairy cows in northeastern China.