Antibiotic growth promoters will be banned from use in the EU from December the 31st 2005, will their loss have a major impact on UK pig production and will we see the same level of disease surge as the Danes?
Concerns arose after Denmark banned growth promoters in March, 1998, as there was a surge in intestinal diseases (diarrhoeas) in weaners and growers and as a result a worrying increase in the use of therapeutic antimicrobials. Proactively the Veterinary Medicines Directorate, an agency of DEFRA, sponsored an on-going research project with Aberdeen University to see what was the likely effect of the removal of antibiotic growth promoters in pigs, as they are the major consumers of antimicrobials.
So what did happen in Denmark when they removed all of the growth promoters? (See Graph 1.)
Graph 1. Growth promoter and therapeutic antimicrobial use in food-producing animals in Denmark
Ref: Danmap 2003
There was a cut off in growth promoter consumption and a steady rise in therapeutic antimicrobial use. Both had been very high during the early 1990's but the therapeutic use was dropping until the ban and it has now risen to its original usage level. Pigs account for 70% of antimicrobial use in food-producing animals in Denmark.
What were the major product groups that were used instead? (See Graph 2.)
Graph 2. Therapeutic antimicrobial use in Danish pigs
Ref: Danmap 2003
Tetracyclines and trimethoprim/sulphas, the two major broad-spectrum antimicrobials for enteric and respiratory disease have grown, aminoglycosides (neomycin and apramycin) for controlling E. coli scours has also increased, this may also be due to the restrictions on the use of zinc oxide at the same time. Surprisingly, use of macrolides almost trebled. This grouping includes tylosin, spiramycin (real macrolides), the lincosamide, lincomycin and the pleuromutilins tiamulin and valnemulin, which all have activity against enzootic pneumonia but more importantly swine dysentery, colitis and ileitis.
So what were the growth promoters doing, other than growth promoting? (See Table 1.)
Most growth promoters have an effect on post-weaning scours, although they are not specifically active against E. coli and would not control it if the environmental conditions were bad. Olaquindox and carbadox were very useful for E. coli control and carbadox is indicated for salmonella control in the US. All of the banned products were very active against Clostridium perfringens, which can cause diarrhoeas in young pigs.
In the UK, what has happened since the partial ban of the growth promoters? Growth promoter figures appear to be fairly static around the 40 tonne mark and overall antimicrobial consumption in food-producing animals is approximately 400 tonnes. There has been a shift though in some of the antimicrobials groups. There are no comparable figures for pig use only. (See Graph 3.)
Graph 3. Changes in the antimicrobial use in UK food-producing animals
Ref: VMD, 2003; (Macrolide figures include tylosin, lincomycin, tiamulin and valnemulin figures for comparison)
The macrolide group (tylosin, lincomycin, tiamulin and valnemulin) has increased quite steadily in comparison with the others. This is mainly due to a switch from tylosin as a growth promoter to a therapeutic for ileitis.
What will happen when growth promoters are withdrawn? For growth promotion alone there are already new products such as potassium diformate and other acidifiers, which will help compensate. As long as zinc oxide is retained, then post-weaning scours should be controlled without an increase in aminoglycoside or trimethoprim/sulpha use. Withdrawal of salinomycin should herald an increase in the use of macrolides for grower pig diarrhoeas. Use of tylosin is likely to increase for ileitis control. Use of tiamulin and valnemulin, the most effective therapeutics for spirochaetal infections such as swine dysentery and colitis, should increase due to the removal of the risk of ionophore interaction, coupled with substitution for lincomycin where tolerance/resistance is a problem. This will have an additional benefit as the pleuromutilins are not used in human medicine and therefore will not compromise antimicrobial therapy in man.
Conclusion
Overall, I think it is likely that the removal of antimicrobial growth promoters will have a relatively minor impact on both pig production and patterns of use of therapeutic antimicrobials by the time it is introduced. Research efforts should be made now to understand our disease problems more, improve our nutrition, management, hygiene and biosecurity, to minimize any impact once a ban is in place.
More on Pig Diseases & Medication: Octagon Technical Papers