Characterisation of Antimicrobial Usage in Small-Scale Commercial Chicken Farms in the Mekong Delta of Vietnam

Nguyen, Van Cuong (2021). Characterisation of Antimicrobial Usage in Small-Scale Commercial Chicken Farms in the Mekong Delta of Vietnam. PhD thesis The Open University.

DOI: https://doi.org/10.21954/ou.ro.000129d2

Abstract

Antimicrobial resistance (AMR) is a global threat to the health and wealth of nations. The AMR crisis has been attributed to the overuse and misuse antimicrobials. Excessive use of antimicrobials in animal production is one of the contributing factors to this global threat. This thesis aims to characterize antimicrobial used (AMU) in small-scale chicken farms in the Mekong Delta region of Vietnam. This includes consumption of antimicrobials mixed with water by the farmer as well those included in commercial feeds as antimicrobial growth promoters (AGPs). The epidemiological data gathered is used to investigate the relationship between AMU and disease.

First, I conducted a systematic literature review to provide an overview of metrics and methodologies used to measure AMU in animal production in the scientific literature, as well as reviewing existing data on AMU in different species in order to identify data gaps worldwide. Then, I performed a longitudinal study on a large cohort of small-scale chicken farms in Dong Thap province in the Mekong Delta region of Vietnam from October 2016 to May 2018 to investigate in detail the types and amounts of antimicrobials consumed, as well as the relationship between AMU and disease. On average, chickens consumed antimicrobials mixed in water over 382.6 per 1,000 days, or 323.4 mg (SEM ±11.3mg) per kg of chicken produced. The average amounts of AAIs in commercial feed given to produce one kg of chicken was 84.8mg (SEM ±9.3mg). Prophylactic AMU did not reduce the probability of disease, and administration of some antimicrobial classes did increase the risk of disease. Therapeutic AMU often had an effect on mortality but the pattern was inconsistent across the combinations of antimicrobial classes and clinical signs. Thirdly, I performed a study in mixed-species small-scale farms typical of the Mekong Delta in order to investigate whether AMU Page 10 of 342 data could be gathered using a simple cross-sectional study design. Results highlight the disproportionately high levels of AMU in animal production in the Mekong Delta region, and provide a guideline for the estimation of AMU from simple cross-sectional surveys on farms.

Results from this thesis suggest that efforts to promote responsible use of antimicrobials and limit excessive AMU should primarily target animal production. The message ‘prophylactic AMU does not overall reduced the probability of disease in flocks’ should be further disseminated to poultry farming communities.

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