Intensive farms make an ideal breeding ground for bugs.
Antibiotics are used in farmed animals for three reasons: to promote growth, to treat disease (therapeutic use) and to prevent disease (prophylactic use.)
In-feed antibiotics tylosin phosphate, virginiamycin, zinc bacitracin and spiramycin were banned in the EU after June 1999, followed by carbadox and oliquindox (60). A total of 7 out of 11 antibiotic growth promoters have been banned in the EU.
However, spiramycin and tylosin phosphate continue to be used for disease prevention (not as growth promoters). Avalymycin continues to be used as a growth promoter, and may be causing resistant VRE (vancomycin resistant enterococci). Use of lincomycin (cross resistant with clindamycin) in pigs is increasing.
There are detailed reports on why antibiotic use in farmed animals is causing a threat to human health (61, 62, 63, 74, 65). Farm use of antibiotics have caused antibiotic resistance to medical drugs in 3 types of food poisoning (salmonella, campylobacter and E coli) and drugs of last resort for treating two strains of the hospital superbug, VRE, which infects wounds and incisions. (70)
Resistance in the food poisoning bacteria has come mainly from using antibiotics routinely to prevent disease. In the case of VRE, resistance has come from using growth promoting antibiotics in farmed animals.
In simple terms, antibiotics have been massively overused by farmers. This has led to bacteria becoming resistant to the drugs so that when the same drugs are used to treat humans, they no longer work.
Although 7 growth promoting antibiotics have been banned, 4 are still in use and others are used to treat and prevent disease. Writers for Pig Farming magazine are against the banning of antibiotics; they say that it will result in increased therapeutic use of drugs (which is true and a reason why factory farming itself has to end).
MAFF state that antibiotics are used more in indoor systems than outdoor (62). Pigs reared in indoor, intensive systems will receive drug treatment throughout their life until slaughter - usually at under 5 to 6 months old. In healthier pig herds antibiotic use may be restricted to injections and growth promoter use. However, in most conventional herds water and feed medication is also practiced.
Diseases and the drugs used
MAFF state (62) that:
Treatment may be given to sows for metritis, mastitis and for diseases such as erysipelas and leptospirosis. In most indoor herds antibiotic treatment starts soon after birth. Piglets will receive drugs for enteritis and for respiratory disease. From weaning (usually 3 weeks) all piglets are gathered, mixed and then reared to finishing weights. Weaners usually develop post weaning diarrhoea caused by E. coli which occurs on day 3 post weaning.
Post-weaning diarrhoea is quickly followed by a range of other diseases. Glassers Disease (haemophilus parasuis) occurs at 4 weeks, pleuropneumonia at 6-8 weeks, proliferative enteropathy from 6 weeks and spirochaetal diarrhoea and colitis at any time from 6 weeks onwards (MAFF 1998).
At 8 weeks the pigs are termed growers and moved to another house. Here they will develop enzootic pneumonia, streptococcal meningitis (Streptococcus suis) and, possibly, swine dysentery. Respiratory disease may cause problems until slaughter (MAFF, 1998).
Quite an indictment of factory farming!
Use of antibiotics varies from unit to unit. In a survey of pig farms in 1995, farms were found which used only penicillin and streptomycin and, perhaps, tetracycline for wounds. These herds were free of most of the diseases requiring treatment. Other herds were infected with a range of diseases and had been prescribed up to 10 antimicrobials (MAFF, 1998) (62).
In a typical herd there is use of neomycin, apramycin, amoxyclav, ampicillin, enrofloxacin or trimethroprim sulphonamide in the diarrhoeic piglets for E coli enteritis (MAFF, 1998).
From weaning pigs will receive feed medicated with a growth promoter. Avilamycin is commonly used. Copper at 175 ppm will be present in all rations. At weaning pigs will receive medication to treat the post weaning E. coli diarrhoea and any Oedema (swelling) disease which may be present.
In 50% of herds the feed is medicated with zinc oxide at 3000 ppm to prevent this and is usually given for two weeks in the feed (MAFF, 1998) (62).
From two weeks after weaning pig feed may contain antibiotics to treat infection with H parasuis, A pleuropneumoniae, S suis (causes meningitis), L intrecellularis. This feed usually contains a tetracycline and is often a combination of chloretetracycline, sulphadimidine and penicillin (MAFF, 1998). The MAFF review adds 'it is important to realise that although each pig may receive a treatment course of a week at most, medication on the farm is continuous, as new pigs inter that age group every week'.
“Major problems with pig farms are the amount of antimicrobials used, the use of tylosin in the farm which results in the presence of Campylobacter resistant to tylosin at slaughter and the contribution made to antibiotic resistance”... (62)
In evidence to the House of Lords select committee, Peter Watson, NOAH chairman of technical affairs and registration and development manager with drug company Bayer, said it was known that:
'two days after you wean the pigs they will develop diarrhoea, and some will become very ill. You include a therapeutic drug over that period to prevent that happening and that is what we understand as prophylaxis” (1998, Evidence, p.208).
The main use of antimicrobials against streptococci in farm animals is for the treatment and control of S. suis (causes meningitis) infection in pigs. Most isolates of S. suis are extremely sensitive to penicillin but resistance has been identified. Treatment is by using penicillin in feed or water. Recently, amoxycillin or amoxyclav have taken over this role (67).
Mycloplasma treatment is particularly frequent in the pig (M. hypneumoniae) and is the reason for the use of significant amounts of antimicrobial (MAFF, 1998). Mycoplasma is an infective agent distinct from bacteria and viruses. The products used eg: tetracyclines, tylosin, tiamulin, lincomycin. Resistance has been identified to all these microbials (MAFF, 1998).
Copper sulphate is often added to the diet which increases growth rate (EU Directives limit the inclusion to 175 ppm for pigs up to 17 weeks, 100ppm for 17 weeks to 6 months, and 35ppm for pigs over 6 mths and breeding stock). Nitrovin is another non-antibiotic growth promoter which is used in the feed (but not with antibiotics). All substances have withdrawal periods before slaughter to avoid residues in the carcass. Although it is admitted that:
"Drug safety is checked by licensing authorities but there is room for misuse, abuse or carelessness of use". (1)