The discovery has fuelled controversy over intensive farming methods and the way antibiotics are used to protect livestock.
Soil Association director Helen BrowningIn the relentless drive for increased per animal productivity... dairy systems are becoming ever more antibiotic dependent
The Soil Association called for a complete ban on routine use of the drugs, which is said to promote the development of drug-resistant bacteria.
It also urged an end to the continuing economic pressure on farmers to cut costs and maintain low prices.
Soil Association director Helen Browning said: "This new evidence confirms our long-held view of the importance of absolutely minimising the use of antibiotics especially those closely related to antibiotics used by people.
"This requires excellent husbandry, and much reduced stress on our animals.
"In the relentless drive for increased per animal productivity, and under acute price pressure, dairy systems are becoming ever more antibiotic dependent.
Are we getting close to PEAK AG? Where we have pushed the animals and the plants so far that they are bad for us?