Prevalence and Risk Factor Analysis of Escherichia Coli–Associated Subclinical Mastitis in Cholistani Cattle

Subclinical mastitis is a major constraint to dairy productivity, particularly in indigenous cattle managed under extensive and semi-intensive systems. The present study investigated the prevalence of Escherichia coli–associated subclinical mastitis, evaluated associated risk factors, and determined the antimicrobial susceptibility patterns of E. coli isolates in Cholistani cattle from Rahim Yar Khan, Punjab, Pakistan. A total of 385 milk samples were collected from lactating cows during 2023–2024 and screened for subclinical mastitis using the Surf Field Mastitis Test. Samples positive for subclinical mastitis were subjected to bacteriological culture on selective media for isolation and identification of E. coli using morphological and biochemical characteristics. Risk factors related to animal, management, and hygiene practices were analysed using univariate and multivariate logistic regression models. Antimicrobial susceptibility of confirmed E. coli isolates was assessed using the disc diffusion method following CLSI guidelines. The overall prevalence of subclinical mastitis was 48.5%, while E. coli was isolated from 20.3% of subclinical mastitis cases. Significant associations were observed between subclinical mastitis and poor milking hygiene, inadequate milker care, high milk yield, body condition, and grazing type. Fluoroquinolones, including enrofloxacin, ciprofloxacin, and norfloxacin, exhibited the highest in-vitro efficacy against E. coli isolates, whereas notable resistance was observed against commonly used antibiotics such as amoxicillin. The findings highlight the epidemiological importance of E. coli in subclinical mastitis and emphasise the need for improved management practices and judicious antimicrobial use to mitigate economic losses and antimicrobial resistance in dairy systems.