Abstract
SummaryAntimicrobials are extensively used both prophylactically and therapeutically in poultry production. Despite this, there are little data on the effect of antimicrobial use (AMU) on disease incidence rate and per cent mortality. We investigated the relationships between AMU and disease and between AMU and mortality using data from a large (n = 322 flocks) cohort of small‐scale chicken flocks in the Mekong Delta, Vietnam, that were followed longitudinally from day old to slaughter (5,566 observation weeks). We developed a parameterized algorithm to emulate a randomized control trial from observational data by categorizing the observation weeks into ‘non‐AMU’, ‘prophylactic AMU’ and ‘therapeutic AMU’. To evaluate the prophylactic AMU effect, we compared the frequencies of clinical signs in ‘non‐AMU’ and ‘prophylactic AMU’ periods. To analyse therapeutic AMU, we compared weekly per cent mortality between the weeks of disease episodes before and after AMU. Analyses were stratified by clinical signs (4) and antimicrobial classes (13). Prophylactic AMU never reduced the probability of disease, and some antimicrobial classes such as lincosamides, amphenicols and penicillins increased the risk. The risk of diarrhoea consistently increased with prophylactic AMU. Therapeutic AMU often had an effect on mortality, but the pattern was inconsistent across the combinations of antimicrobial classes and clinical signs with 14/29 decreasing and 11/29 increasing the per cent weekly mortality. Lincosamides, methenamines and cephalosporins were the only three antimicrobial classes that always decreased the mortality when used therapeutically. Results were robust respective to the parameters values of the weeks categorization algorithm. This information should help support policy efforts and interventions aiming at reducing AMU in animal production.
Highlights
Antimicrobials play a critical role in the maintenance of animal health, animal welfare and food safety (FAO, 2016) and are used worldwide in food-producing animals for the prevention and treatment of infectious diseases
For the prophylactic antimicrobial usage (AMU) analysis, these were x, the duration of the observation period; y and z, the numbers of weeks filtering for previous presence of clinical signs and AMU, respectively; and a, the duration of the first few weeks of the flock during which we look for potential AMU
Our analyses show that the significance of the effect of prophylactic AMU on clinical signs tends to decrease as the duration of the observation period increases, suggesting that the effect of AMU may be of relatively short term, typically 2 weeks
Summary
Summary Antimicrobials are extensively used both prophylactically and therapeutically in poultry production. There are little data on the effect of antimicrobial use (AMU) on disease incidence rate and per cent mortality. We investigated the relationships between AMU and disease and between AMU and mortality using data from a large (n = 322 flocks) cohort of small-scale chicken flocks in the Mekong Delta, Vietnam, that were followed longitudinally from day old to slaughter (5,566 observation weeks). Prophylactic AMU never reduced the probability of disease, and some antimicrobial classes such as lincosamides, amphenicols and penicillins increased the risk. Therapeutic AMU often had an effect on mortality, but the pattern was inconsistent across the combinations of antimicrobial classes and clinical signs with 14/29 decreasing and 11/29 increasing the per cent weekly mortality. Results were robust respective to the parameters values of the weeks categorization algorithm This information should help support policy efforts and interventions aiming at reducing AMU in animal production. | 484 prophylactic and therapeutic effects of antimicrobials from 13 different classes on diarrhoea, respiratory infections, legs lesions and central nervous system infections. We show that prophylactic antimicrobial use never reduced the risk of diseases and that some classes increased the risk of some diseases (e.g. diarrhoea). In small-scale flock settings, the therapeutic use of antimicrobials leads to an increase in mortality in about 50% of the investigated antimicrobial/disease combinations
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