It turns out that antibiotics are not the gift that keeps on giving. Our most potent weapon for fighting bacterial infections since Alexander Fleming discovered penicillin in 1928, antimicrobials have been badly blunted by misuse and overuse, to the point where the World Health Organization (WHO) has declared antimicrobial resistance (AMR) one of the top 10 global public health threats to humanity.

And for good reason: 1.2 million people perished directly from antibiotic-resistant infections in 2019 according to a global analysis published this year in The Lancet, more deaths than from either HIV/AIDS or malaria, while another study of AMR predicts 10 million annual fatalities by 2050.

WHO highlights rising resistance to antibiotics used to treat common and preventable diseases such as urinary tract infections, sexually transmitted diseases, sepsis and some forms of diarrhoea. Especially alarming is the rapid spread of multi- and pan-resistant bacteria – the so-called ‘superbugs’.

The global response to the threat has inevitably thrown a spotlight on farming and veterinary medicine. At least 80% of global antimicrobial use is for animals (no surprise, really, given that in many cases ‘the patient’ receiving the dose will be a 500kg cow) and many of those antibiotics are critically important for human health. Mark Bryan, chair of the New Zealand Veterinary Association’s AMR Committee, remembers attending a One Health conference soon after WHO released its 2015 Global Action Plan on Antimicrobial Resistance, which stressed the need for a multi-sectorial, One Health response.

“There was a lot of attention on veterinarians and their prescribing activities. We felt like we were in the firing line. We looked at ourselves and asked, ‘Could we do better?’”

New Zealand is actually relatively light-handed in the use of antimicrobials for animals. We’re one of the three best-performing OECD countries (after Norway and Iceland), reflecting among other things a pastoral farming system that produces less disease than others. “We hold up really well,” says Mark, “but of course you always must do better. At the end of the day we want to be prudent stewards of antimicrobials.”

The NZVA has publicly committed to achieving zero use of antibiotics for the maintenance of animal health and wellness by 2030. Bryan calls it an “aspirational” goal, aimed at raising awareness and pushing everyone to raise their game. “It speaks to the fact that we should be managing diseases better and changing the focus to one of prevention and management techniques,” he says, adding that the vision is that “we have the same suite of antibiotics available in 2030 and they’re still effective”.

Meanwhile, the Ministry for Primary Industries (MPI) and the Ministry of Health have led the development of a national action plan that picks up on WHO’s five AMR objectives to: improve awareness; strengthen the evidence base; improve infection prevention and control measures across human health and animal care; optimise the use of antimicrobials; and establish clear governance and collaboration so that initiatives are sustainable. Warren Hughes, principal adviser for agricultural compounds and veterinary medicines in the Assurance Directorate of New Zealand Food Safety, has been involved in the operational management of AMR for a decade.

“The goal is to preserve what we have, because there aren’t a lot of new antibiotics coming through,” he says, noting that sales data shows a decline in antimicrobial use in NZ.

“You see other countries making huge gains, but that’s because their use was quite high. We’re trending in the right direction, but there will be a plateau stage where it’s difficult to go any lower, because you do need antibiotics. It’s about hitting that sweet spot.”

Reaching that point is going to require better monitoring of AMR and antimicrobial use. Hughes points out that NZ Food Safety has been collecting antibiotic sales figures since 2004, but there’s now a push to get more granular data, right down to the level of antibiotic use at individual veterinary clinics. As well, NZ Food Safety this year received additional funding to extend its AMR surveillance from postmortem to live animals. Improved monitoring will help to identify trends and highlight any potential “hot spots”, he says.

Simultaneously, MPI is doing a deep dive review of all antibiotics used for animals in this country, starting with the tranche that are critically important for human health. The outcome, according to Hughes, is likely to involve changes to controls and to product labelling to underscore the need for prudent use. He notes that NZ’s legislation allows the regulator a fair bit of flexibility to move quickly.

“For example, we removed advertising to the end user for antibiotics of human health importance, and we did that through the controls on individual products rather than having to change legislation.”

Hughes describes veterinarians as “key risk managers in the chain”, not least because antibiotics of human health importance require veterinary authorisations or must be prescribed by veterinarians. But what concrete changes has the veterinary profession made to mitigate the dangers of AMR?

For starters, the NZVA has developed judicious-use guidelines for each farm animal sector, establishing principles on which practices can anchor their prescribing habits. For the dairy sector, for instance, one core principle is that “antibiotics should only be used by a veterinarian when there is evidence of a susceptible bacterial infection, treatment is necessary to maintain animal health and welfare, and no other treatment such as drainage or antisepsis is likely to be effective”.

The association has also instituted a traffic-light system for antimicrobials. The idea is that: green-light antibiotics (less important for human health) should be preferred as first-line therapy; orange-light products are restricted to specific indications or as a second-line approach; and precious red-light antibiotics are only to be used on a case-by-case basis following veterinary diagnosis and with sufficient evidence of need.

Bryan says the focus on reducing the use of red-light antibiotics has proved effective – although it hasn’t been without challenges. “Whether it’s due to convenience or habit, veterinarians and farmers get used to using antibiotic A, even though antibiotic B or antibiotic C would do the job,” he says. “It’s been a matter of demonstrating that these new treatments are just as effective, and that takes time. But it’s been successful. When you go around clinics, a lot have labelled their antibiotics red, orange and green. At the same time farmers have understood why we’re doing this. The red-light antibiotics are hardly ever used now, and when they are it’s only for cases that are sensitive to those antibiotics – which is exactly where we want to be.”

In tandem with reducing antibiotic use, the veterinary profession is working with industry to develop alternative ways of managing animal health and wellbeing, with an emphasis on improving infection prevention and control. In the poultry sector, for instance, there’s been a significant shift to vaccinate against various diseases, helped by the development of new vaccines since 2015.

“Poultry have some specific diseases that are really challenging to manage, and a switch away from antibiotics was always going to be difficult. But we’ve seen leaps in reduced use as the sector has made progress,” Bryan says, adding that other measures include mitigating stress and finding new ways to boost immune systems. “Lots of things are being done to make a difference.”

In dairy the big challenge is mastitis, which is responsible on a daily-dose basis for 85% of antibiotic use in the sector. Once upon a time so-called dry cow therapy was applied at the end of lactation on a whole-herd basis, but in the 1990s the emphasis shifted to a more selective approach with subsequently some mission creep.

“We saw a period in which there was an increase in herds and cows being treated with antibiotics for drying off, partly driven by milk processors saying we needed to keep our bulk milk somatic count [an indicator of mastitis] down,” says Scott McDougall, a veterinarian and Professor of Dairy Cattle Health at Massey University, whose area of expertise includes the treatment of mastitis and antimicrobial usage and resistance.

“In the past five years there’s been a concerted effort by veterinarians and DairyNZ to move back more strongly to selective dry cow therapy. The message is, you should only be using antibiotics on cows who really need them.”

As part of this, agreement was reached between the NZVA’s Society of Dairy Cattle Veterinarians branch, DairyNZ, and milk processors for a unified message about the need for selective dry cow therapy.

Simultaneously, there’s been a big push for prevention. The use of teat sealants as an alternative to antibiotics is an obvious example of prevention in practice, but McDougall also notes a raft of smaller improvements in farming practices.

“It could be as simple as making sure there’s no pooling of water or faeces in raceways. When cows are walking to a milking parlour, the idea is that they walk calmly and quietly and don’t have to stop at right angles where they all pile up and defecate.

“Where standoff or feed pads are used, it’s about making sure they’re really clean. Another important area for mastitis control is teat spraying – putting an antiseptic on a teat after a cow has been milked.”

Improved veterinary communication on the issue with farmers has also made a difference. “The introduction of dry cow therapy consultations, with veterinarians having structured conversations with farmers at least once a year and working to identify where improvements can be made, has been really important,” he says, remarking that having DairyNZ and dairy processors on board hasn’t hurt.

“It’s useful for veterinarians when they’re talking to farmers to be able to say, ‘It’s not just veterinarians saying this – it’s the whole industry’.”

As for optimising use, that’s been helped by getting a clearer picture of onfarm AMR.

“We’ve seen the development and commercialisation of tools that allow veterinarians to know the resistance patterns of the mastitis bugs on the farms they deal with. Now a veterinarian can say to an individual farmer, ‘Look, you have resistance to this particular drug on your farm, so we’re not going to use it because it won’t be effective.

“We’ve seen behaviour change as a result, including a reduced use of drugs such as Tylosin, a red-light antibiotic.” So how much further can we reduce antibiotic use in dairy? “One thing we need to be clear about is that this is not about reducing drug use for the sake of it,” McDougall says. “By international standards, our drug use in the dairy industry is reasonably good, and we need to be careful not to go too far. There are international examples, such as in veal calves in the Netherlands, where use was reduced to such a level that we saw welfare issues – the pendulum swung too far. I think we can make improvements by doing more in terms of prevention and getting a better uptake of known disease-control programmes.”

Vaccination is an important part of that.

“For instance, we have vaccines for pregnant cows that protect their calves against some of the common causes of diarrhoea. There’s bovine viral diarrhoea [BVD], too. It’s a viral disease but also an immune suppressant, so if we can use vaccines and testing programmes to get BVD out of herds it has a flow-on effect.”

Whatever further steps are taken on antimicrobial use, farmers will need to be convinced, Mark Bryan says. “You don’t get behavioural change by telling people what to do; it’s much better to have some co-designed processes where they’re involved in the change.”

He cites a recent three-year initiative to reduce antimicrobial use in southern NZ, which focused on encouraging farmers to develop antimicrobial use-reduction strategies.

“By the end of it we had 160 farms using various strategies and their antibiotic use had reduced by 40%. Many of the strategies took account of things we’d been saying for years, but because the farmers had articulated them and developed the practical applications, their adoption was better.” The programme has since been rolled out nationally.

Finally, what about antimicrobial use and companion animals? Mark notes that while the volume of antibiotic use may be lower, there are proportionally more red-light drugs in play.

“The focus has really been on managing those red- and orange-light antibiotics, getting them used as judiciously as possible. From what I can see, companion animal veterinarians have taken it to heart. There’s been an improvement in disease prevention, even in things like routine surgery. For example, we no longer give desexed cats antibiotics because if we’re practising sterile surgery we shouldn’t need to. It makes a big difference.”

• First published in the NZVA VetScript Oct/ Nov 2022.