Overall sales of antibiotics in veterinary medicine and horticulture appear to have dropped, the Ministry for Primary Industries says.
But a new report also voices concerns about emerging trends in how some drugs are used.
An analysis of antibiotic sales from 2009 to 2011 showed a decrease of 19% during that period, but also found a significant increase in the use of injectable tylosin in dairy cattle for the treatment of mastitis.
The report says the greatest risk to antibiotic resistance is the use of this drug within animal production, and it recommends other treatments be used where possible.
The ministry said the use of tylosin will be investigated further, along with an emerging trend of the choice of antibiotics being based on convenience, rather than because they're the most appropriate treatment.