Background Senecio jacobaea contains pyrrolizidine alkaloids that can induce severe hepatic intoxication in horses, either acute when ingested in high amounts or chronic when consumed over a long period. The aim of this study was to determine horses’ rejection behaviour towards the presence of Senecio jacobaea in hay when fed ad libitum. We hypothesized that adult horses can sort Senecio jacobaea out of the contaminated hay when hay is fed ad libitum. Six warmblood geldings with a mean (±SD) age of 15 ± 2 years were included. In a randomized study, Senecio jacobaea contaminated hay (5% or 10% contamination level) was provided at several timepoints over the day for 1 hour to six. Hay was provided ad libitum for the rest of the day. The horses’ rejection behaviour towards Senecio jacobaea was observed. If a horse ingested two Senecio jacobaea plants twice at different timepoints, then the horse was excluded from the experiment. Results Two out of six horses had to be excluded from the study after three out of 12 observation periods due to repeated Senecio jacobaea intake. Two other horses had to be excluded after nine and 11 out of 12 observation periods. Only two horses were able to sort out the various amounts (5 and 10% contamination level) of Senecio jacobaea during the whole experiment. Conclusions Horses’ intake of Senecio jacobaea cannot be avoided despite being fed with hay ad libitum. Due to the risk of chronic intoxication by pyrrolizidine alkaloids intake, feeding Senecio jacobaea contaminated hay must be avoided, and pastures with Senecio jacobaea growth are considered inappropriate for feed production.

Background Extensively used grasslands are frequently utilised for hay production for equines. Especially, extensive meadows have a great variety of plant species, which may include plants that are poisonous for equines such as meadow saffron (Colchicum autumnale L.). To authors’ knowledge investigations about horses` avoidance behaviour towards dried meadow saffron in hay are missing. Reports of farmers are contrary to clinical symptoms described in case reports and associated with meadow saffron in hay. Objectives The aim of this study was to determine the rejection behaviour of horses for hay contaminated with meadow saffron (MS) when fed ad libitum. Study design An 18‐day feeding trial with six adult geldings to observe the rejection behaviour for hay contaminated with MS. Methods The horses were fed a basal diet containing hay ad libitum and a mineral supplement during the feeding trial. At six different daytimes, hay contaminated with 1% or 2% dried MS was provided to the horses over a duration of 1 h. The rejection behaviour was observed personally and by video recordings. If a horse ingested more than two plants of MS during one observation period, the observation was stopped and repeated at another day. When the observation period had to be stopped twice, the horse was excluded from the experiment. Results Five of six horses ingested MS during the first feeding periods. One horse rejected leaves and capsules at the beginning of the study, but it showed repeated ingestion of MS after the seventh observation period. Main limitations Lack of knowledge about secondary plant metabolites affecting taste and their variability between fresh and dried plants. Conclusions The intake of MS in hay by horses could not be ruled out with certainty. Therefore, feeding hay contaminated with MS should be avoided for equids.

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