Data on how and why medically important antibiotics are used in agricultural settings—and the implications of that—are central to ensuring the judicious use of these drugs. Yet this information is limited in availability. The only national estimates of total antibiotic use in food animal production come from sales data. Important progress has been made in improving this information—notably, the Food and Drug Administration’s most recent data broke down sales estimates by major food animal species (chickens, cows, pigs, and turkeys) for the first time—but much more detailed information is needed.
A recent FDA proposal to establish a method for estimating the size of the animal populations potentially being treated with antibiotics could help address this challenge and provide context for sales numbers—a welcome improvement. Ultimately, however, data on actual antibiotic use are needed.
Q: What is animal biomass, and how is it applied to antibiotic sales data?
A: Biomass refers to the total mass of an animal species’ population that may require antibiotics. For the purpose of putting antibiotic sales data in context, biomass is generally calculated from the number of food-producing animals in a country during a given year and their average weights.
This information can provide useful insights and help explain trends and fluctuations in antibiotic sales, which may be affected by differences or changes in animal populations.
For example, adjusting sales data by a country’s biomass numbers could help account for variations in antibiotic use driven by differences in animal weight and population size due to such factors as:
Composition of the animal population (species and breeds). For example, chickens weigh significantly less than pigs or cows, and beef cattle tend to weigh more than dairy cattle.
Average animal life spans. For example, the average broiler chicken lives for just over a month, whereas cattle tend to live for at least two years, leading to significantly different periods when antibiotics might be required.
Animal management practices. Some animals, such as cattle, can be slaughtered at varying ages and weight ranges, and keeping animals longer can increase the biomass of the species. Such practices can differ considerably by country.
Further reading: PEW Trusts