Introduction
Aquaculture represents a particularly critical sector amongst animal production concerning antimicrobial usage (AMU) and its potential impacts on animal health and the surrounding environment. In Italy, official AMU data are not systematically collected: while some regions have performed the collection in regional datasets, others lack reliable information (Scoppetta et al., 2018). Within Italian aquaculture, rainbow trout holds a central role, as it constitutes the most extensively produced species, placing Italy among the leading European producers. Approximately 70% of national trout production is concentrated in North-eastern Italy where, there is a representative spectrum of structural, managerial and environmental conditions across different farming systems. This research project aims to quantify AMU and to estimate the trend of antibiotic consumption in the provinces of Trento and Udine (primary areas of rainbow trout farming in the North-East of Italy). This activity constitutes a preliminary step towards the development of a standardised national methodology for data collection and a subsequent investigation into the factors influencing the AMU.
Materials and Methods
To define the study population, data from the national livestock registry were used. These data were processed to create lists divided by the provinces involved (Udine and Trento), including all establishments intended for human consumption that kept at least the species rainbow trout. These lists were submitted both to the competent territorial veterinary authorities (ASUIT and ASUFC) and to the trade association (API) for validation. ASUIT and ASUFC provided data on pharmacological treatments carried out in the selected establishments over the three-year period 2022–2024, through access to the national information system which collects all prescriptions issued for farmed animals. Production data, expressed in kilograms of slaughtered and/or marketed fish for each selected establishment, were provided by API, which collects them annually.
AMU was calculated using a dose-based methodology, which makes it possible to take into account the potency of each commercial formulation in relation to a specific treatable biomass, known as the Population Correction Unit (PCU). The data were processed in Define Daily Dose Animal for Italy (DDDAit) to obtain a tailored profile for the commercial products used in Italy. Briefly, the DDDAit of an antimicrobial medicinal product refers to the quantity of active substance, expressed in milligrams, that should be given per kilogram of live body weight each day of treatment, in accordance with the summary of product characteristics (SPC). This metric is the one established during the development of the ClassyFarm management system (it is a national IT platform that collects and processes a significant amount of data relating to animal welfare, biosecurity on farms, antimicrobial consumption and susceptibility, etc.), which currently does not consider fishes but only some terrestrial species. In Italy, the trout slaughter weight varies depending on the type of final product required; for the purposes of this study, we have estimated an average weight of 1 kg. According to the literature (Narbonne et al., 2021), a reasonable treatment weight can be taken as half the slaughter weight meaning in our case 0.5 kg. The total number of fish can be approximated by dividing the annual slaughter biomass by this 1 kg reference weight. This estimated fish count, together with the assumed average treatment weight of 0.5 kg per animal, can then be used to calculate the PCU for each selected establishment.
Results and Discussion
Overall, data were collected for 57 farms. The AMU derived from the calculation represents the number of days of antimicrobial treatment to which each animal farmed on the establishment may have been potentially exposed during the period considered, in our case one year. The results show high variability between different farms as well as within the same farm over the years: there are indeed years in which no pharmacological treatments were administered and others in which the AMU value dramatically increases. This aspect will be investigated further through the subsequent statistical analysis planned within the project, in which possible associations between AMU and risk and protective factors will be assessed (the factors taken into account will include both management and environmental considerations). There are farms (21%) that did not carry out any treatments over all three years considered. An investigation into their characteristics showed that these are farms with a favourable geographical location (altitude, and therefore ideal water temperature, and considerable distance from other farms) and which did not experience relevant bacteriological issues. In these cases, as well, it will be of interest to examine whether the only protective factors are geographical, or whether there are also management-related aspects. According to the EMA's proposed classification of antimicrobials, by examining the data from all the farms, 2022 alone saw a peak in the use of class B antimicrobials; on closer inspection, this was attributable to a single farm that used large quantities of flumequine, having resorted to this class of drugs due to serious fish health issues. In both 2023 and 2024, however, class B accounted for the smallest percentage of antimicrobials used, with classes C and D predominating.
Conclusions
In conclusion, this study highlighted the feasibility of applying a dose-based approach to calculate AMU in trout farms. Preliminary data show considerable variability both between farms and over time, with a non-negligible proportion of farms showing no treatments over extended periods. The subsequent analysis of risk factors will allow for a better understanding and explanation of the observed variability.
Acknowledgment
This research is funded by the Ministry of Health, RC 06/24 "Assessment of environmental, management, and structural factors for reducing antibiotic consumption in farming and improving the health and welfare of rainbow trout (TROUTment)" (CUP: B23C24000880001).
References
Scoppetta F, Chiovoloni M, Spernanzoni G, Filippini G, Capuccella M. (2018) Pharmaco-epidemiological evaluation of veterinary antimicrobial prescriptions for cattle, swine, small ruminants, poultry, rainbow trout, and food-producing horses in Umbria in 2014. Vet Ital. 2018 Dec 31; 54 (4):305-315. doi: 10.12834/VetIt.1174.6524.2.
Narbonne J.A., Radke B.R., Price D., Hanington P.C., Babujee A. and Otto S.J.G. (2021). Antimicrobial Use Surveillance Indicators for Finfish Aquaculture Production: A Review. Front. Vet. Sci. 8:595152. doi: 10.3389/fvets.2021.595152