Histophilus somni as a Unique Causative Agent of Puerperal Metritis (PM) in a Third-Lactation Holstein Cow

This manuscript aims to report the clinical and laboratory diagnosis of puerperal metritis (PM) in a dairy cow, caused by H. somni as a unique pathogen. The cow showed signs of systemic illness, including a sudden drop in milk production, a rectal temperature of 40.4 °C, tachypnea, dehydration, and completely fluid, brown, and fetid uterine discharge. Pure cultures of H. somni were identified and submitted to the Kirby-Bauer disc diffusion method for antibiotic sensitivity. The study showed that H. somni was resistant to tetracyclines and cephalosporins (Ceftiofur), antibiotics commonly used to treat uterine infections in dairy cows. To the authors' knowledge, this case describes for the first time PM caused by H. somni as a primary pathogen. Our results should lead to the inclusion of H. somni as a primary pathogen of metritis in laboratory diagnoses on a routine basis, which, in turn, may help to elucidate the incidence of H. somni as a causative agent of uterine infections in cows. If the incidence of H. somni is remarkably high or frequent, researchers could consider the use of commercial vaccines nowadays destined for the prevention of bovine respiratory disease and which could perhaps be effective in the prevention of reproductive pathology caused by H. somni.