This was primarily due to fewer treatments in the seawater phase, where just a slight increase in the number of treatments can significantly alter overall use statistics because bigger fish require a bigger dose.
The figures are included in a report by Ruma (Responsible Use of Medicines in Agriculture Alliance) which summarised progress against antibiotic use targets identified by the UK livestock industry’s Targets Task Force in October 2017.
Among lowest in Europe
The Task Force is addressing the threat that routine use of antibiotics in farming can lead to pathogens developing antimicrobial resistance which could threaten human health because drugs would then be ineffective against disease.
UK sales of antibiotics for food producing animals have fallen 53% since 2014 to 30 mg/kg5 and are one of the lowest in Europe.
Highest-priority Critically Important Antibiotic (HP-CIA) sales for food producing animals have fallen 68% between 2014 and 2018 from an already low level, and 19% between 2017 and 2018. No HP-CIAs were used in salmon or trout farming in 2018.
The Ruma report said antibiotic use in salmon totalled 1,011.3 kg, which equated to 6.5 mg/kg of production and was slightly higher than an “ambitious target” of 5 mg/kg established for the sector in 2017.
“However, it is important to highlight that significant differences occur in required dosing for the various available antibiotics and the majority of antibiotics used in 2018 were either oxytetracycline hydrochloride (58.0%) or florfenicol (40.8%), requiring larger doses of active ingredient, with minimal use of oxolinic acid (1.2%), requiring smaller doses,” explained Ruma, which warned against setting too much store on single-year figures.
“The production cycle of farmed salmon can be as long as three years, with up to a year spent in freshwater and up to two years in seawater. Consequently, appraising use in individual years is not necessarily representative and it is important to look at longer term trends in the usage data.”
The report added: “Although antibiotic use decreased in 2018, environmental challenges were still evident and the sector remains mindful that variable environmental conditions (for example due to global climate change) may impact health management in the future. Usage figures to date and in the future will therefore reflect a balance between minimising antibiotic use and ensuring fish health and welfare.”
The trout sector in England and Scotland also reduced antibiotic use, by 32% compared to 2017, using 13 mg/kg.
Ruma stated: “The trout sector has made considerable progress against targets in this second year. While salmon producers tend to be integrated into defined supply chains, trout producers are mostly small, independent operators. This means the challenges they face are extremely diverse, not least of which is lack of access to effective vaccines.”
The beef sector used 21 mg/kg of antibiotics last year, and the dairy sector used 17 mg/kg. The poultry meat sector used 12.4 mg/kg in 2018, and in the sheep sector mean use from separate flocks ranged from 3 to 17 mg/kg.
The pig sector, which relies more heavily on antibiotics, is on track to meet its target of 99 mg/kg by 2020, down from 278 mg/kg in 2015.
Read the full report here.