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Herd Health Program Participation Associated with Lower Vancomycin Resistance and Multidrug Resistance in Dairy Mastitis Pathogens: A Five-Year Surveillance Study in Saraburi, Thailand
by
, , and
Sirirat Wataradee
1,2
,
Witaya Suriyasathaporn
3,4,5,
Maneerat Somsee
2,6,
Sukuma Samngamnim
1,
Amonthep Khuprathumsiri
2,6,
Kittisak Ajariyakhajorn
1,2 and
Thanasak Boonserm
1,2,* 1
Department of Veterinary Medicine, Faculty of Veterinary Science, Chulalongkorn University, Bangkok 10330, Thailand
2
Dairy Research and Technology Transfer for Tropical Dairy Development Center (TDRC), Faculty of Veterinary Science, Chulalongkorn University, Saraburi 18110, Thailand
3
Veterinary Academic Office, Faculty of Veterinary Medicine, Chiang Mai University, Chiang Mai 50200, Thailand
4
Research Center of Producing and Development of Products and Innovations for Animal Health and Production, Chiang Mai University, Chiang Mai 50200, Thailand
5
Overseas Campus, Asian Satellite Campuses Institute, Nagoya University, Nagoya 464-8601, Japan
6
Large Animal Teaching Hospital, Faculty of Veterinary Science, Chulalongkorn University, Bangkok 10330, Thailand
*
Author to whom correspondence should be addressed.
Biology 2026, 15(10), 782; https://doi.org/10.3390/biology15100782 (registering DOI)
Submission received: 11 April 2026
/
Revised: 4 May 2026
/
Accepted: 12 May 2026
/
Published: 14 May 2026
(This article belongs to the Special Issue Large Animal Experimental and Epidemiological Models for Diseases)
Simple Summary
Bovine mastitis, which is routinely treated with antibiotics, is the costliest disease in dairy farming. When bacteria become resistant to these drugs, treatment fails and resistant organisms can spread to people through milk or direct contact. This study examined 1347 milk samples from 47 smallholder dairy farms in Saraburi Province, Thailand, over a five-year period (2020–2025). Some farms participated in a veterinary herd health program that included monthly veterinary visits, laboratory-based diagnosis before treatment, and farmer training on milking hygiene and responsible antibiotic use; other farms relied on symptom-based treatment without veterinary guidance. Farms outside the program were roughly four times more likely to harbor bacteria resistant to vancomycin—a last-resort antibiotic for serious human infections—and 2.5 times more likely to harbor multidrug-resistant bacteria. Resistance rates also fell markedly after 2023, when a regional Dairy School and local veterinary center were established. Yeast infections, a hallmark of antibiotic overuse, occurred only on non-program farms. These findings provide the first evidence from Thailand that structured veterinary oversight and farmer education are associated with lower rates of resistance to critically important antibiotics in dairy systems, supporting their adoption as part of national antimicrobial stewardship policy.
Abstract
Antimicrobial resistance in bovine mastitis pathogens poses interconnected threats to dairy productivity and public health; however, longitudinal evidence on the association between veterinary oversight and lower resistance to critically important antimicrobials in tropical smallholder systems remains limited. This study analyzed 1347 quarter milk samples from 47 dairy farms in Saraburi Province, Thailand, submitted consecutively over five years (2020–2025), to evaluate whether participation in a veterinary-led herd health (HH) program was independently associated with reduced vancomycin resistance and multidrug resistance (MDR). Bacterial identification was conducted using standard methods, and susceptibility was determined using the Kirby–Bauer disk diffusion method. Among 1069 culture-positive samples, Streptococcus spp. (25.3%) and coagulase-negative staphylococci (16.8%) predominated. Vancomycin resistance declined from 15.9% to 5.4% between early (2020–2022) and recent (2023–2025) periods. Of the 686 isolates tested against ≥3 antibiotic classes, 61 (8.9%) were MDR; vancomycin resistance co-occurred in 34.4% of these samples. Repeated logistic regression identified non-HH farm status (OR = 4.035; p = 0.027) and early-year groups (OR = 4.611; p = 0.002) as independent risk factors for vancomycin resistance. As HH participation and year group showed a significant interaction, their joint effect for MDR was modeled: compared with non-HH farms in the early period (reference), all other combinations—including HH farms in 2023, HH farms in 2020, and non-HH farms in 2023—were associated with significantly lower odds of MDR. These findings provide the first evidence from Thailand that structured veterinary herd health programs are independently associated with lower critically important antimicrobial resistance, supporting their integration into a One-Health stewardship policy.
