Occurrence of Mastitis Associated with Histophilus somni

Abstract

At the end of April 2015, a six-year-old Holstein cow suffered from mastitis in the left fore and rear quarters at a dairy farm in the middle of Yamaguchi Prefecture. It partially recovered after treatment, but relapsed at the beginning of May. Histophilus somni was isolated from a milk sample of the left forequarter with a bacterial count of 1.7×10⁴ CFU/ml. Mastitis became chronic after a series of antibiotic treatments and the affected quarter was permanently dried off in mid-June. One month later, H. somni was not isolated from this cow or other cattle at the farm. Between 1999 and 2015, 23 total H. somni strains were isolated from clinical samples in Yamaguchi Prefecture and were examined by sequence analysis of its major outer membrane protein (MOMP) gene. Phylogenetic analysis of the MOMP gene indicated that the strain in this study was genetically unique from the other 22 strains of H. somni. The current study suggests that mastitis with H. somni is sporadic and has a tendency to become chronic.