Homeopathy is widely used in livestock, especially to replace or reduce the use of antibiotics in the treatment of infectious diseases, although its use is often seen as controversial. For organic agriculture, homeopathy is even promoted.
In the review, Dr Caroline Doehring and Professor Albert Sundrum from the University of Kassel, Germany, assessed peer-reviewed studies on the efficacy of homeopathy in cattle, pigs and poultry published between 1981 and 2014.
They analysed a total of 52 clinical trials, 34 with cattle, 12 with pigs and six with poultry. They were published in 48 publications.
Of these, 28 concluded that the homeopathic remedy administered was effective, 22 showed no efficacy and 2 were inconclusive.
Only 10 trials provided information on cure rates for the treatments. These varied to a high degree, while the remedy used did not seem to make a big difference.
Trials on pigs were frequently efficacious, while studies with cattle or poultry had a similar distribution of efficacious and non-efficacious treatment.
Double-blind randomised controlled trials reported efficacy of the homeopathic treatment almost as often as they reported lack of it.
Meanwhile, single-blind and non-blind randomised controlled trials, and observational trials were more likely to present evidence of efficacy, suggesting that positive outcomes may be due to bias.
Other study limitations, such as potential conflict of interests, low sample size, risk for selective reporting and bias, were found in the majority of trials.
While some clinical trials showed effectiveness, the authors of the review question the reliability of the evidence, because all studies had a range of limitations. For example, all clinical trials were conducted under very specific conditions and none were repeated under comparable conditions.
Therefore, the authors say the findings cannot be be used to recommend homeopathy: "The current evidence of studies providing evidence in favour of homeopathy lacks reproducibility and therefore cannot claim to have sufficient prognostic validity."
"Due to a lack of prognostic validity, replacing or reducing antibiotics with homeopathy currently cannot be recommended unless evidence of efficacy is reproduced by RCTs and proven in various farm practice conditions."
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