Prevalence and cow-level risk factors for mild and severe subclinical mastitis in intensive and extensive dairy systems in Bangladesh
摘要
Subclinical mastitis (SCM) substantially limits dairy productivity in Bangladesh, yet evidence from high-density herds remains limited. This cross-sectional study estimated the prevalence of mild and severe SCM and identified cow-level risk factors in 3,173 lactating cows from 76 herds in Sirajganj District, Bangladesh (January 2023–December 2024). Composite milk samples were tested using an EKOMILK SCAN® analyzer to measure somatic cell count (SCC), and cows were classified as healthy, mild SCM, or severe SCM using SCC distribution-based thresholds. Cow-level data were collected using structured questionnaires. A Bayesian hierarchical multinomial regression model, with herd as a random effect, was used to estimate relative risk ratios (RRR). Overall, 1,517 cows (47.8%) had mild SCM and 578 cows (18.2%) had severe SCM, with comparable prevalence between extensive and intensive systems (66.4% vs 65.9%; chi-square p = 0.836). Lactation stage showed severity-specific effects: late lactation credibly increased mild SCM risk (RRR 1.758; 95% CrI 1.306–2.365) but not severe SCM risk, whereas early lactation credibly increased severe SCM risk (RRR 1.595). History of clinical mastitis was the strongest predictor of severity: relative to cows with two prior episodes, severe SCM risk was higher with one episode (RRR 5.754; 95% CrI 2.709–12.533), three or more episodes (RRR 5.162), or no prior history (RRR 2.131), similarly for mild SCM. Lower parity and higher milk yield credibly reduced SCM risk; Holstein Friesian and Jersey crosses had credibly lower mild SCM risk than Sahiwal crosses, and pregnant cows had credibly higher mild SCM risk. Targeted surveillance of late-lactation and mastitis-history cows may improve SCM control in high-density herds.