Oral antibiotic use in calves has more than doubled in a year, putting new pressure on dairy farms to reduce antimicrobial use and increasing calls to focus on vaccination as a practical solution.
The new RUMA figures show sales of oral antibiotics for calves increased from 1.92 mg/kg daily defined dose (DDDvet) for animals to 4.03 mg/kg DDDvet in 2024.
In response, the industry group introduced a new target to reduce the use of oral antibiotics in calves by 10% compared to the previous year.
At the same time, King Shay’s latest data for 967 dairy herds across 136 veterinary clinics shows that overall antibiotic use continues to decline.
Average usage decreased from 12.7 mg/kg in 2024 and 15.7 mg/kg in 2020 to 12.2 mg/kg PCU in 2025.
However, antibiotic use remains concentrated within a small group of farms.
Herds in the top quartile of antibiotic use accounted for 50% of the total antibiotics used.
In these high-use herds, oral products (often administered to calves for respiratory disease and abrasions) accounted for 13% of total use.
Although the King Shay data show that calf oral antibiotic use decreased from 1.38 mg/kg PCU to 1.05 mg/kg PCU between 2024 and 2025, different datasets measure separate indicators, highlighting that oral calf treatment remains a key focus for the field.
Emma Paddy, expert at Kingshay Farm Services and co-author of the report, said the use of oral antibiotics in calves can significantly increase antimicrobial numbers across the farm.
“When we use oral antibiotics in calves, we find that the usage is probably significantly higher than the group average,” she said.
“Oral antibiotics actually tend to increase overall antibiotic use.”
She explained that injectable treatments are typically used on individual animals, while oral products are often administered to whole cages when the risk of disease increases, increasing the total mg/kg metric.
High levels of antimicrobial use can impact benchmark performance and place farms under increased scrutiny from supply chains and warranty systems.
King Shay training consultant and veterinarian Michael Head said reducing usage starts with understanding disease incidence through a robust herd health plan.
“An effective vaccination strategy is part of this, as people tend to reach for antibiotics. However, the benefits of strong immunity, genetic advances and good nutrition make cows more resistant to disease, thereby reducing the need for antibiotics,” he said.
Despite this, AHDB vaccine data shows that less than 50% of calves are vaccinated against respiratory diseases, and only about a quarter of producers vaccinate against calf dermatitis.
Head said new vaccines targeting cryptosporidiosis and bovine mycoplasma could help change the situation.
“Vaccine use is certainly increasing rapidly and we are already hearing farmers encouraging other farmers to use the vaccine,” he said.
He also warned that the calf’s illness would have lasting effects.
“Disease in calves has significant implications for the future health, longevity and disease resistance of those animals,” he said.
Dr. Kat Baxter-Smith, veterinarian at MSD Animal Health, said the findings highlight the real opportunity for vaccination and management changes for farms looking to reduce antimicrobial numbers.
“Respiratory disease and warts remain the two most common reasons antibiotics are used in young calves,” she said.
“By addressing these challenges early through vaccination and proper management, farmers can significantly reduce the need for antimicrobial interventions.”
He noted that versicolor caused by cryptosporidiosis can be difficult to manage, pointing to reports of paromomycin resistance in E. coli K99.
Vaccination, combined with proper housing, ventilation, and colostrum management, can reduce disease pressure and support increased lifelong performance, resilience, and productivity.
Farmers are encouraged to review calf health plans with their veterinarians prior to the next calving season, especially if oral antibiotics are routinely used in group treatments.
