Epidemiology of Subclinical Mastitis in Dairy Cows of Monaragala District, Sri Lanka: Prevalence, Risk Factors, Bacterial Etiology, and Antimicrobial Resistance
Abstract
A cross-sectional study was conducted in the Monaragala District of Sri Lanka to assess the prevalence, bacterial causes, antibiotic resistance patterns, and associated risk factors of subclinical mastitis (SCM) in dairy cows. Five veterinary surgeon (VS) divisions were selected using a simple random sampling method, and 607 lactating cows from 175 dairy farms were chosen through multi-stage stratified random sampling. SCM was diagnosed in each cow via the California Mastitis Test (CMT). Cows testing positive for CMT (≥2+ for any quarter) without clinical symptoms were considered SCM positive. Milk samples from positive cows were bacteriologically isolated and tested for antimicrobial susceptibility. Risk factors for SCM incidence were identified using multivariable generalized estimating equation (GEE) models and descriptive statistical analysis. The SCM prevalence was reported as 18.7% at the cow level, 26.8% at the farm level, and 10.75% at the quarter level. Staphylococcus aureus (79.1%) and Staphylococcus epidermidis (16.4%) were the most commonly isolated pathogens. Antimicrobial susceptibility testing demonstrated significant resistance to ampicillin (67.6%), neomycin (89.8%), and sulfamethoxazole-trimethoprim (60.2%). In contrast, the majority of isolates remained susceptible to enrofloxacin (81.1%). Multidrug resistance was noted in 31.8% of isolates, with S. aureus reporting the highest prevalence. Multivariable analysis detected parity, lactation stage, mastitis history, breed, production system, floor hygiene, and cleaning frequency as risk factors. In conclusion, SCM in Monaragala District was predominantly associated with contagious pathogens and influenced by both animal- and farm-management factors. Antimicrobial resistance was common among mastitis-associated bacterial isolates.
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References
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