A huge review of scientific papers on homeopathy in livestock animals dating back to 1981 has concluded that there is insufficient evidence to support its use to treat diseases. Though the review, published in the Veterinary Record, revealed that most clinical trials showed homeopathy to be effective, the authors questioned the reliability of their evidence.

Homeopathy is based on the idea that ‘like cures like’ - so a substance that would cause certain symptoms in a healthy body could be used to treat the same symptoms in a sick one - and treatments involve diluting an active substance in water so that its ‘memory’ remains. It is fairly widely used to treat livestock, and supporters of homeopathic methods tout it as one means of reducing antibiotics use. Earlier this year, Defra figures showed there were 500 farmers trained in homeopathy and 38 vets, though the British Veterinary Association (BVA) does not endorse the practice.

Even so, homeopathy does have some influential adherents. Prince Charles uses homeopathic treatments on cows and sheep on his 360 ha Home Farm estate. In May this year the Prince told medical experts assembled in London “I converted my farming operation to an organic system over 30 years ago and… we have been successfully using homeopathic – yes, homeopathic – treatments for my cattle and sheep as part of a programme to reduce the use of antibiotics.”

In the past, MPs with ministerial briefs including Jeremy Hunt and a number of Labour front benchers have courted controversy by expressing support for the approach.

In their review, Dr Caroline Doehring and Professor Albert Sundrum from the University of Kassel, Germany, assessed studies on homeopathic treatment of cattle, pigs and poultry published over a period of more than 30 years (1981-2014). They studied reports on homeopathic remedies, which were suggested to replace or prevent the use of antibiotics or promote growth in food producing animals. These included 52 clinical trials, with 34 in cattle, 12 in pigs and six in poultry.

Overall, 28 trials were in favour of homeopathy, 26 showed significantly higher efficacy in comparison to a control group, and 22 found the approach had no discernible effect. However, as all the trials were conducted under very specific conditions, and none were properly repeated, the reviewers said they “Cannot be be used to recommend homeopathy.”

Only 10 trials provided information on cure rates for the treatments and these varied greatly, while the remedy used did not seem to make a big difference. The researchers did note that trials on pigs seemed to work the best.

Interestingly, Double-blind randomised controlled trials - the gold standard approach in medical research - found that homeopathic treatment was effective almost as often as they showed no effect. However, less stringent single-blind and non-blind trials were more likely to show that treatments worked, which the reviewers suggested may indicate bias. They also found other issues with studies, including potential conflict of interests, low sample sizes, and potential selective reporting and bias in “the majority” of cases.

"A considerable number of studies demonstrated a significantly higher efficacy for homeopathic remedies than for a control group," the authors said. "Therefore, the potential medical efficacy of homeopathy under certain conditions cannot be ruled out."

However, they added, ”The current evidence… in favour of homeopathy lacks reproducibility and therefore cannot claim to have sufficient prognostic validity."

Reacting to the review in a joint statement, Professor Peter Lees of the Royal Veterinary College and Prof Pierre-Louis Toutain from the European Board of Veterinary Specialisation underlined the importance of replicating results in medial and veterinary science (none of the studies were replicated). They remarked that “Conclusions based on single clinical trials (either positive or negative) cannot be conclusive."

The pair said, “It is the most comprehensive review on homeopathy in farm animals yet published,” but highlighted that “Of 48 publications identified, 33 were published in homeopathic journals. In contrast to homeopathic journals, [12 out of 18 trials in] journals with a broader focus on veterinary medicine found the homeopathic treatment was ineffective.”

They concluded, “The review authors emphasise that animal welfare considerations demand that treatments applied should always be the most effective to avoid unnecessary suffering.  Justifying homeopathic products on grounds of concerns with conventional/pharmacological-based treatments is not justified.”

Dr Martin Whitehead, a vet at Chipping Norton Veterinary Hospital, agreed that the review showed indications of bias in a number of papers. Dr Whitehead said, “Part of the study does show that better designed trials were less likely to show a positive effect of homeopathy. Some of the 28 positive trials will be ‘false positive’ due to bias.” However, he added, “Some of the trials demonstrating no benefit will have been in comparison to conventional treatment, and may possibly have demonstrated benefit relative to placebo-treated control group.”