Pigs account for the majority (approximately 60 per cent) of farm antibiotic use in the UK (108). The Veterinary Medicines Directorate shows that in 2010, an estimated 211 tonnes were sold for use in pigs, 138 tonnes for poultry, 11 tonnes for cattle, one tonne in fish and less than 0.5 tonnes were sold for use in sheep.
Use of antibiotic per animal for pigs, 2007 to 2010 (grammes of active ingredient per animal per year)
Source: Soil Association (108)
Antibiotics are used in farmed animals for three reasons: to promote growth; to treat disease (therapeutic use), and to prevent disease (prophylactic use).
An EU-wide ban on the use of antibiotics as growth promoters in animal feed came into effect on January 1, 2006 (109). On the surface this sounds a positive move; however, antibiotic use remains high.
Intensive farms make ideal breeding grounds for bugs. However, factory farmed pigs are routinely fed antibiotics, even when they are healthy. The high stocking density, the stress of factory farming on animals and the low level of genetic diversity all increase the potential for the spread of diseases amongst animals. To stop the spread of diseases, factory farms usually use high levels of antibiotics, often to prevent disease rather than cure existing conditions.
However, it is widely known that pigs are fed antibiotics to make them grow more quickly. Though growth promoting antibiotics have been banned, more are simply used but under the label of disease prevention.
The use of antibiotics to increase the growth of pigs is most studied of all livestock. This use for growth rather than disease prevention is referred to as sub-therapeutic antibiotic use. Studies have shown that administering low doses of antibiotics in livestock feed improves growth rate, reduces mortality and morbidity, and improves reproductive performance. Although it is still not completely understood why and how antibiotics increase the growth rate of pigs, possibilities include metabolic effects, disease control effects, and nutritional effects (110).
The large amount of antibiotics used in factory farming is a significant cause of the resistance of many common pathogens to the antibiotics used to treat infections in humans.
Antibiotics are administered as standard on factory farms © Viva!
There are detailed reports on why antibiotic use in farmed animals is causing a threat to human health (108, 111, 112, 113). <<we don’t have that 1999 report any more>>
According to the Alliance to Save our Antibiotics, the overall weight of scientific research has led to a consensus (114) that:
· for some bacterial infections, such as Campylobacter and Salmonella, farm antibiotic use is the principal cause of resistance in human infections.
· for other infections, like E. coli and enterococcal infections, farm antibiotic use contributes, or has contributed, significantly to the human resistance problem.
· the emergence of resistance to critically important antibiotics, in particular of ESBL resistance in E. coli and Salmonella, is a major development which has occurred in recent years and has been driven by inappropriate use of these antibiotics in both human and veterinary medicine.
· livestock-associated strains of MRSA infecting humans are also a developing problem, which results from the high use of certain antibiotics in farmed animals.
· some other emerging antibiotic resistant infections in humans may be, in part, due to farm antibiotic use, but while research is ongoing, there is currently insufficient evidence to draw clear conclusions.
The lack of major success over past decades in developing new antibiotics means that it has become ever more important that we preserve the antibiotics that we have by using them only when they are genuinely needed in order to reduce overall use.
On many highly intensive pig (and chicken) farms, the approach is to increase hygiene and ‘biosecurity’ to reduce the spread of disease. However, the widespread use of some disinfectants can also select for antibiotic-resistant bacteria.
A main concern is that agricultural antibiotic use is driving up levels of antibiotic resistance, leading to new "superbugs". Most public health experts agree that resistant bacteria are created in ‘food’ animals by antibiotic use and that some of these are being transmitted to people and one of the major concerns to emerge in connection with such over-use is new E.coli and MRSA superbugs on farms (108).
In December 2015, it was reported that 12 people had been treated for infections linked to virulent strains of salmonella and E.coli carrying a deadly resistance gene (115). In November 2015, scientists sounded the alarm over the dangers of global epidemics caused by infections that doctors would not be able to treat. The warning followed the discovery of a superbug version of E.coli on pig farms in China. It contained the MCR-1 resistance gene that disables the last-line antibiotic colistin, which would normally be used to treat humans after all other drugs have failed. Now this same resistance gene – MCR-1 – has been found in bacteria in people, farmed animals and meat in Britain (116). There is an urgent ongoing review into the alarming discovery, which demonstrates that superbugs are a clear and present danger for British families.
A 2015 report, which was part of an ongoing review of antimicrobial resistance (AMR), produced by an independent body chaired by a British economist, stated that farmers must dramatically cut the amount of antibiotics used in agriculture, because of the threat to human health (113). The report also revealed that 72 per cent or 100 of 139 academic papers found evidence of a link between antibiotic consumption in animals and resistance in humans. Only seven (5 per cent) argued that there was no link between antibiotic consumption in animals and resistance in humans. The review also showed that a considerable amount of antibiotics are used in healthy animals to prevent infection or speed up their growth in confined conditions (113).
For some bacterial infections, such as Campylobacter and Salmonella, farm antibiotic use is the principal cause of resistance in human infections (117). For other infections, like E. coli and enterococcal infections, farm antibiotic use contributes, or has contributed, significantly to the human resistance problem (117). The emergence of resistance to critically important antibiotics, in particular of ESBL resistance in E. coli and Salmonella, is a major development which has occurred in recent years and has been driven by inappropriate use of these antibiotics in both human and veterinary medicine (117).Bacteria that produce enzymes called extended-spectrum beta-lactamases (ESBLs) are resistant to many penicillin and cephalosporin antibiotics and often to other types of antibiotics. The two main bacteria that produce ESBLs are E. coli and Klebsiella species.
E. coli with ESBLs may cause urinary tract infections (UTIs) that can sometimes progress to more serious infections like blood poisoning, which can be life threatening. Resistance makes these infections more difficult to treat.
Farmed animals, particularly pigs, are a reservoir for powerful new bacteria which are a threat to human health, suggests a Government study (118).
Any humans infected through food or contaminated water with these bugs - new strains of E.coli and campylobacter - are at serious risk (118). As a result, a whole raft of drugs will no longer be useful in treating conditions including TB, other lung infections and food-poisoning (118).
Antibiotic Research UK’s Director says the chances of salvaging the most important drugs are 50-50 after resistant bacteria were found in pigs and humans in England and Wales (119). It is “almost too late” to stop a global superbug crisis caused by the misuse of antibiotics, a leading expert has warned. He also stated that said efforts to find new antibiotics are “totally failing” despite significant investment and research. It comes after a gene was discovered which makes infectious bacteria resistant to the last line of antibiotic defence, colistin (polymyxins) (119).
The resistance to the colistin antibiotic is considered to be a “major step” towards completely untreatable infections and has been found in pigs and humans in England and Wales. Resistance is thought to have grown due to colistin being heavily used in pockets of the agricultural industries, particularly in China, often to increase the physical size of livestock (119).
In the UK, nearly half of all antibiotics used are in farming (119); and worldwide the figure is the same (120, 121). The unnecessary prescription and use of antibiotics as a form of treatment is also believed to be an aggravating factor.
The overuse of antibiotics props up factory farming systems in which animals are at a greater risk of illness due to close confinement, early weaning and stress. The underlying reason for food-animal-related antibiotic resistance is the dependence on antibiotics of this type of intensive farming. Animals not in need of treatment are nevertheless dosed with antibiotics to compensate for the suppression of their immune systems – brought on by overcrowding, early weaning, high stress and other aspects of the unnatural production systems in which they are reared. And the desire to force the growth of the animals – to get them to slaughter as quickly as possible, fuels massive antibiotic overuse.