A dog suffering from acute diarrhoea (under 14 days) has been brought to your clinic and no cause is identified. The owners suggest the feeding of a probiotic to shorten the recovery time, based on their findings on the internet. You have no experience in recommending a probiotic supplement as diarrhoea management. What evidence exists to support this approach?
Five placebo-controlled studies were identified that have assessed the clinical outcomes of administering a daily oral probiotic supplement in dogs that have acute diarrhoea with no identifiable cause.
Significant findings were reported for various outcome measures: the time to diarrhoea resolution; improvement in diarrhoea severity; change in the microbiota; and the percentage of dogs that required additional treatment.
Three studies presented a shorter time to diarrhoea resolution in the probiotic group, ranging from 15 hours to 2.7 days. However, detailed investigations of the underlying aetiology of the diarrhoea were either incomplete or patients with identified causes were included.
The studies may not be sufficiently strong to support a faster clinical recovery by the probiotic supplement, because baseline variations between the probiotic and placebo group were not evaluated, a standardised definition of abnormal stool was not given to owners and clinicians, there was an unexplained mismatch between the number of dogs that completed one study and the number of dogs included in the analysis of diarrhoea resolution and a validated stool scoring system was not used.
Two studies measured improvement in diarrhoea severity in the probiotic group. One reported a greater improvement in stool consistency score in the probiotic group than the placebo on day seven. However, the improvement differed from the placebo group by such a small degree that it was questionable whether there was an observable difference in stool quality, and whether the improvement in consistency score was clinically relevant. Also, this study did not evaluate baseline variations between the probiotic and placebo group.
The second study that measured improvement in diarrhoea severity reported that the probiotic group took one day less to achieve a statistically significant improvement in the “Canine Haemorrhagic Diarrhoea Severity Index”. Given that clinicians and owners may have different standards when they evaluate the costs and benefits of a one day improvement, the clinical relevance of this study is unclear.
The probiotic group in the first of these two studies presented a greater decrease of faecal C. perfringens on day seven, while the probiotic group in the second study presented a lower abundance of faecal C. perfringens. The clinical relevance of these findings is affected by the undefined relationship between C. perfringens and acute diarrhoea.
It is unclear whether a reduction of C. perfringens in faecal samples can be regarded as a clinical benefit, given that one study reported an association between increased C. perfringens in faeces and acute diarrhoea, while another was unable to find an association between the two.
Two studies showed a lower percentage of dogs in the probiotic group received additional treatment than the placebo group, and a large sample size of 118 was included in one of these.
In conclusion, the participating dogs in all the studies presented a better clinical improvement in the probiotic group than the placebo. This suggests a daily supplement of oral probiotic may provide better clinical outcomes to dogs experiencing acute diarrhoea without an identifiable cause. One study offered fairly strong evidence for a reduced requirement of additional treatment in dogs administered a probiotic.
The clinical relevance of the reduction in faecal C. perfringens and improvement in diarrhoea severity was uncertain, and the strength of the studies supporting a shorter time to diarrhoea resolution was limited.
Additional studies would be beneficial to validate the better clinical outcomes brought by probiotic supplementation, given there were variations in several factors, which can lead to different clinical outcomes.