A report on New Zealand sales of antibiotics for animals and plants that ultimately affect human health holds bad, worse and good news - depending on whether you're a food consumer or a data cruncher for the Government.

The bad news is total antibiotic sales via veterinary medicines and agricultural chemicals rose 8 per cent in the two years between 2014 and 2016 year-end, compared to the previous reporting period 2011/2012-2014, says the Ministry for Primary Industries (MPI) which collects sales data on antimicrobials, also known as antibiotics.

The lift could be attributed in part to an increase in animal and plant production, MPI said.

The good news, according to MPI, is there was a drop in the sales of three classes of antibiotics that are considered by the World Health Organisation (WHO) to be of "highest priority critical importance to human health". They are third and fourth generation cephalosporins; fluoroquinolones and macrolides.

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But sales of the class aminoglycosides, mostly used in horticulture and classed by WHO as "critically important", continued to increase during the two years.

Penicillin and bacitracin sales also increased, while most other antibiotic class sales decreased, said the report.

Resistance to antibiotics - and their over-prescription - are global concerns, threatening medical ability to prevent and treat infectious disease caused by micro-organisms including bacteria, parasites and fungi.

Further into the MPI report, antibiotic volume sales in the five years between 2011 and 2016 went from 59,350kg to 68,350kg - an increase MPI partly attributed to a 39 per cent increase in the poultry population and a 6.5 per cent increase in dairy animals.

"These populations use a considerable amount of the antibiotics sold compared to other populations due to the more intensive farming practices," said the report.

Aminoglycoside sales - almost entirely to the kiwifruit industry for treatment of the Psa bacterial border invader that devastated the sector from 2010 - lifted 23 per cent during the five years.

The increase was in part due to the subsequent increase in land used for kiwifruit growing, the report said.

Most antibiotics sold were administered to animals in feed. Injectable products were second most common sales.

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Antibiotics registered for use specifically for cattle accounted for 14 per cent of sales, said the report. Mostly they were used to treat milking issues. Cattle provide milk and meat.

Antibiotics registered for use on horses comprised 4 per cent of sales between 2014 and 2016 while dogs and cats claimed 2.5 per of sales registered for their use.

The report said the poultry population increased 15.3 per cent between 2014 and 2016, from 107.4 million birds to 123.8m.

Caged egg laying hen numbers held steady at 3.6m birds.

The report estimated free range chickens for eating increased from 13m in 2014 to 21m in 2016.

Free range egg-laying chicken numbers climbed from 650,000 in 2014 to 1m in 2016.

The report data was collected from veterinarians and the agricultural sector.

MPI concluded that systems in place to manage animal health and encourage prudent use of antibiotics were working - though New Zealand could continue to improve.

"While there has been an overall increase in the quantities of antimicrobials sold, it is clear that practices of antimicrobial use are changing to reflect concerns...."