Antimicrobial substances have played a very important role in pig production for decades, whether originally used for just growth promotion but also for therapeutic purposes. I am delighted to have been asked to comment on this subject as we are facing another onslaught of regulations in the EU over the next couple of years. Let us hope they have learnt from their previous mistakes. In this column I will focus on what has happened in the past, what the situation is today – and what might be ahead of us in the years to come.
I think it is useful to look at the past and see if we can learn from some of the 'precautionary principle' changes that were made on the basis of very little scientific evidence or understanding. Back in the 90s there was concern that antimicrobial resistance could be transferred from animals to man and that the use of prescription-free antimicrobials was the potential cause of such things as vancomycin resistance in Enterococci species and the growing threat of methicillin-resistant Staphylococcus aureus (MRSA) in man, which was being treated by vancomycin (similar to Avoparcin) and streptogramins (similar to Virginiamycin).
Antibiotic growth promoters were included in feed by feed compounders without a veterinary prescription and in some countries were very popular. I think it was not understood by the authorities that most of these antibiotics were also active against disease causing pathogens in the gut. Denmark was the first to ban all growth promoters in the EU, unilaterally, in 1999.
This led to a tremendous switch from a usage of growth promoters of about 107 tonnes and therapeutic antimicrobials 56 tonnes in 1997 to 0 tonnes of GPs (-100%) in 2000 and 81 tonnes of therapeutic antibiotics (+45%) (see Figure 1). This continued to increase to 94 tonnes (+68%) with a doubling of tetracyclines and trimethoprim/sulphas and a trebling of macrolides, lincosamides and tiamulin use. Presumably, this was to compensate for the increase in enteric diseases reported. In the UK, when growth promoters were banned in the EU in 2006, a different picture was seen. (see Figure 2)
There was little change in the therapeutic use of antibiotics, as they knew the ban was coming for a number of years and had had time to experiment with alternatives to be able to compensate, unlike in Denmark. I think this was pretty much the same position in most of the EU countries. Later, there was a reduction of therapeutic use of antibiotics in pigs, which was probably associated with the introduction of PCV2 vaccines at the time.
Several countries have introduced monitoring of antimicrobial use such as Denmark, the Netherlands, France, Belgium and Germany. ESVAC is developing an EU position on this. Benchmarking and in some cases targets for antimicrobial use, based on political whim/dogma, rather than science-based assessments, have also been introduced. Some antimicrobials have been voluntarily banned from use like the 3rd and 4th generation cephalosporins and fluoroquinolones in some countries.
Now we are under threat from the EU Commission to introduce further regulations to change the way veterinarians use antibiotics therapeutically. In-feed medication is their major target for reducing overall use of antibiotics, especially in pig production. In-feed medication accounts for 85% of antibiotic use in pigs in the UK. The Dutch have banned its use and this has brought their antibiotic consumption down dramatically by over 50%. Has this had any effect on the major concerns of transmission of resistance from animals to man? It is possibly too early to say, but the human equivalent (Nethmap 2013) reported that there had been no effect on human resistance, which was still increasing.
I still strongly believe that most of the antimicrobial issues in humans relate directly to human use of antibiotics and the EC admits that they do not know what contribution of resistance to human health is from animal use. My own work shows that the contribution of critically important antibiotic resistance to human cases from pigs, including MRSA, is 0.00038% and poultry 0.135% - please prove me wrong. It must be remembered that both the cephalosporins and fluoroquinolones are not approved for in-feed use in the EU; hence I think the EC approach potentially is flawed.
It is hard to predict, but there is a strong political lobby to reduce the use of antimicrobials in veterinary medicine and in pigs in particular. The current EC regulation proposals want vets to stop using antimicrobials for prevention. In-feed use and prevention do tend to go hand in hand, to get the best response from feed medication the pigs must be eating. From an animal health and welfare perspective, a complete ban on using antibiotics for preventing bacterial infections is crass. A metaphylactic approach, when you know animals are infected and likely to break with disease must be permitted. To wait for infected animals to develop clinical disease and some possibly die before you treat them makes no sense and against all veterinary principles.
Yes, vets and farmers must use antibiotics more responsibly and effectively and try to adopt production systems that can reduce antibiotic use. I believe monitoring and examining our use is an important part of this but if we have to follow the current over-restrictive regulation proposals without prior preparation, I can see a disaster looming, similar to that which the Danes saw when they first banned antibiotic growth promoters.