Industry calls for more research into resistance

1 May 1998

Industry calls for more research into resistance

INCREASING pressure to find effective antibiotics for human use is driving the move to ban certain antibiotics for animal use, but more research on development of resistance must be done before action is taken.

The Lords Select Committee report on resistance to antibiotics, released last week, says that antibiotics used in vet medicine and as growth promoters in animal feed pose a continuing threat to human health. It calls for some growth promoters to be phased out and use of certain antibiotics in animal medicine to be controlled.

But SAC vice-principal and past president of the British Veterinary Association, Karl Linklater, explains that increasing resistance concerns in human medicine means that antibiotics previously agreed for use in animals are now being retained for medical use as the last line of attack.

"The Swann report of 1968 identified certain antibiotics for use in humans. Groups which were most removed from these were allowed to be used as growth promoters, but these are now being looked at for medical use – hence the recent ban on avoparcin."

But Prof Linklater says that more research must be done on development of resistance. "We must know more about how infections spread from humans to animals and vice versa, and how resistant strains develop.

"There has been some research, but we need to know under what circumstances resistance develops and quantify the implications of resistance."

According to Prof Linklater, recording the number of incidences of resistance is of little use. "There might be only one case of resistance which spreads through the population. In this case, recording incidence will pick up the diffusion rather than development of resistance."

Glos-based vet Roger Blowey agrees that resistance concerns are far more complex. "Despite long-term use of dry cow therapy – cloxacillin has been widely used for the last 30 years – I am not aware of any resistant strains of staphylococcus or streptococcus. This shows that resistance development is by no means straightforward."

He also backs the use of dry cow therapy on welfare grounds. "We are criticised for getting only two or three lactations out of cows, but dry cow therapy helps to increase longevity."

Antibiotic use – primarily as growth enhancers – is widespread in the pig industry, but declining, explains nutritionist Caroline Bevan. "Growth enhancers are generally used from start to finish, but alternatives such as enzymes, probiotics, acids and herbs are being examined by producers. But none of these is as rigorously tested, which is worrying as we dont know what effect they are having."

Prescription drugs are used to control diseases such as pneumonia, but Mrs Bevan stresses that most producers try to minimise their use because of the high costs involved. "However, if a disease is on farm and cannot be eradicated there may be no option other than in-feed medication as welfare has to be considered."

Poultry producers routinely use antibiotic digestive enhancers to ensure optimum liveweight gain, but there are other benefits, explains British Vet Poultry Association spokesperson Catrina Webster. "These additives produce evenly sized flocks which reduces welfare concerns.

"While some producers are using products such as probiotics or enzymes, these are being used in addition to growth enhancers; there are no products which will replace growth enhancers."

Although the Lords Select Comm-ittee report identified beef production as an area where antibiotic growth promoters are widely used, SAC nutritionist Mitch Lewis disagrees. "Intensive finishers are the most likely users of these products, but the promised liveweight gain benefit is probably 0.05-0.1kg a head a day – not much where cattle are achieving 1.3-1.4kg DLWG."

However, antibiotic use in the sheep industry, where lambs on some farms are routinely given antibiotics at birth, is a concern, and must be tackled, urges consultant Lesley Stubbings.

Reduce disease risk

"Some producers choose to dose all lambs to reduce disease risk, and consequently there are some incidences where resistance has developed and producers have had to select different products.

"These producers must think about why they are dosing lambs – particularly when ensuring they receive enough colostrum soon after birth should help protect against disease. At least wait until you see symptoms before giving antibiotics, or be selective in their use an only dose high risk lambs such as triplets."

Correct use of antibiotics is a concern of the BVA, which has recently drawn up a code of practice for their use, as Prof Linklater explains. "The code recommends use of a narrow spectrum antibiotic initially, coupled with a sensitivity test to ensure correct product selection. If that product does not help control infection, then a broader spectrum product should be the next option."

Antibiotic use – primarily as growth enhancers – is widespread in the pig industry, but is declining. Alternatives are available, but not as well tested.


&#8226 Resistance complex.

&#8226 More research required.

&#8226 Quantify implications.

By Emma Penny

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