Stringhalt in Brazilian horses caused by Hypochaeris radicata

Two outbreaks of Hypochaeris radicata-induced Australian stringhalt involving two farms and seven horses from southern Brazil are reported here. Subsequently, the disease was experimentally reproduced in a feeding trial with one colt fed H. radicata from the suspect paddocks. Fresh H. radicata was fed to the experimental animal for 50 days at an average daily dosage of 9.8 kg. Initially, the plant was collected from the paddock where the clinical disease occurred and was fed for 19 consecutive days producing mild clinical signs. However, on days 20-23 fresh plant was collected from a neighboring farm where the disease had not been reported and fed to the colt at which time the colt appeared to recover. Therefore, plant collections from the original suspect paddock resumed and feeding trials continued with clinical signs reoccurring by day 36, and increasing in intensity from days 43-50 after which plant administration was stopped. Within 15 days after ending the feeding trial with H. radicata, the colt appeared to have recovered. This experimental reproduction of stringhalt in a single colt fed H. radicata demonstrated that the two outbreaks of the disease resulted from this plant. Interestingly, the change in location for collection of plant material 19 days into the treatment, and the subsequent recovery of the colt, would suggest that plant material may differ in toxicity depending on location.