Abstract

Background:
Subclinical mastitis (SCM) is a major constraint in peri-urban smallholder dairy production. Inconsistent biosecurity and milking hygiene may increase infection risk and productivity losses.

Aim:
This study aimed to assess the association between biosecurity practices (external, internal, and procedural) and SCM prevalence and severity in peri-urban dairy farms in Greater Jakarta (Jakarta, Bogor Regency, Bogor City, and Depok), Indonesia.

Methods:
A cross-sectional survey was conducted in 34 eligible smallholder dairy farms from April to June 2025 using structured interviews, direct observations of biosecurity practices, and California Mastitis Test (CMT). Farmlevel SCM severity was defined as moderate (1) if ≥1 tested cow had CMT 2–3 in any quarter, and mild (0) otherwise. Associations were assessed using chi-square tests and binary logistic regression, and model performance was evaluated using receiver operating characteristic analysis (SPSS v26).

Results:
The prevalence of cow-level SCM was 72.9% (105/144; 95% CI: 65.7%–80.2%), ranging from 57.1% in Depok to 90.2% in Bogor City. For farm-level analyses (n = 34), 16 of 34 farms (47.1%) were classified as moderate and 18 of 34 (52.9%) as mild. Procedural biosecurity was significantly associated with SCM severity (mild vs. moderate; χ² = 6.959, p = 0.008), whereas external and internal biosecurity were not (p > 0.05). In the parsimonious logistic regression model, a higher farmer education category was associated with higher odds of moderate SCM [odds ratio (OR) = 1.369, p = 0.027], whereas procedural biosecurity was protective (OR = 0.449, p = 0.011). The final model demonstrated good discrimination (area under the curve = 0.845).

Conclusion:
Procedural biosecurity (milking and hygiene-related practices) was the only biosecurity dimension significantly associated with SCM severity and was protective against moderate SCM in peri-urban smallholder dairy farms in Indonesia. Strengthening cost-effective milking hygiene and targeted farmer training may help reduce the SCM burden in comparable settings.

Key words: Biosecurity; Subclinical mastitis; Dairy cattle; Peri-urban farming; California Mastitis Test.