Horses’ rejection behaviour towards the presence of Senecio jacobaea L. in hay

Despite having a distinctive smell, horses were poor discriminators of hay containing the toxic weed Tansy Ragwort. It should not be incorporated into hay.
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Horses’ rejection behaviour towards the presence of Senecio jacobaea L. in hay
BMC Vet Res. 2022 Jan 7;18(1):25.
Authors
Louisa Sroka 1 , Clara Müller 1 , Marie-Lena Hass 2 , Anja These 3 , Sabine Aboling 2 , Ingrid Vervuert 4
Affiliations

1 Institute of Animal Nutrition, Nutrition Diseases and Dietetics, Faculty of Veterinary Medicine, Leipzig University, Leipzig, Germany.
2 Institute for Animal Nutrition, University of Veterinary Medicine Hannover, Hannover, Germany.
3 Department Safety in the Food Chain, German Federal Institute for Risk Assessment, Berlin, Germany.
4 Institute of Animal Nutrition, Nutrition Diseases and Dietetics, Faculty of Veterinary Medicine, Leipzig University, Leipzig, Germany. ingrid.vervuert@vetmed.uni-leipzig.de.

Abstract

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.

Keywords: Ad libitum; Pyrrolizidine alkaloids; Selection behaviour; Tansy ragwort; Toxic plants.