Horses fail to reject toxic plant in hay trial, researchers find

The autumn crocus, Colchicum autumnale, flowers in a meadow in Lauterbourg, in the Alsace region of France. Photo: Aloxe, Free Art License, viat Wikimedia Commons
Meadow saffron (Colchicum autumnale), also known as the autumn crocus, flowers in a meadow in Lauterbourg, in the Alsace region of France. Photo: Aloxe, Free Art License, via Wikimedia Commons

Hay contaminated with meadow saffron, also known as autumn crocus, poses a risk to horses, the findings of fresh research show.

Meadow saffron (Colchicum autumnale) is a common plant species in extensively used grasslands.

It is found across mainland Europe from Portugal to Ukraine, as well as in Great Britain and Ireland. It is also reportedly naturalized in Denmark, Sweden, European Russia, the Baltic states, and New Zealand.

In spring, its leaves develop with a tulip-like capsule that contains seeds. Due to this, leaves and capsules of meadow saffron are usually found in hay. Late harvesting favours the dispersal of seeds.

Meadow saffron contains the alkaloid colchicine and its derivatives. Colchicine inhibits cell division in tissues and causes a wide range of symptoms in horses, such as colic, blood in the urine, or coughing.

Clara Mueller and her fellow researchers, writing in the Journal of Animal Physiology and Animal Nutrition, noted that although horses have been observed to avoid meadow saffron in pastures, it is unclear whether this is the case with horses fed hay-based diets.

On one hand, Austrian farmers have reported that horses avoid the plants in hay. On the other hand, case reports have linked clinical symptoms in horses with meadow saffron contamination in hay.

The study team, therefore, set out to assess the ability of horses to reject meadow saffron in hay.

A feeding trial with six adult geldings was conducted to observe the rejection behaviour for hay contaminated with meadow saffron.

The horses were kept in individual stalls, with daily turnout to a paddock for several hours.

They had free access to good quality hay, as well as receiving a mineral supplement.

In the feed trial, the horses were offered hay manually contaminated with 1% or 2% of meadow saffron, but never for more than an hour. Their rejection behaviour was observed personally and through video recordings.

If a horse ingested more than two meadow saffron plants during one observation period, the observation was stopped and repeated another day. Once observation periods had to be stopped twice, the horse was excluded from the experiment. Withdrawal after the second ingestion of meadow saffron was designed to ensure there were no toxic effects. Blood parameters before and after the experiment were also found to be within normal physiological ranges.

The authors found that five of the six horses ingested meadow saffron during the first feeding periods.

One horse rejected leaves and seed capsules at the beginning of the study, but it showed repeated ingestion of meadow saffron after the seventh observation period.

Hunger as a cause of intake can be rejected, they said, because the horses had access to plenty of hay.

The authors said that the intake of meadow saffron by horses cannot be excluded even when they have unlimited hay access. “The reasons for the intake of meadow saffron are not fully understood in horses.

“Four horses even preferred the intake of meadow saffron compared to hay.”

The authors noted that EU regulations state that feed shall not be marketed or fed to any food-producing animal if it is unsafe. Feedstuffs are unsafe if they are considered to have an adverse effect on animal health. Such feedstuffs would include hay contaminated with meadow saffron.

The EU Regulation (EC) 767/2009 extended the ban to non-food-producing animals. Additionally, colchicine is considered a prohibited substance for food-producing animals based on EU Regulation 37/2010, which may also be applied to slaughter horses.

“Since intoxication by meadow saffron cannot be excluded from the routine feeding practice in horses, meadows containing MS are not suitable for hay production.”

The study team comprised Mueller, Louisa Sroka, and Ingrid Vervuert, with Leipzig University in Germany; Marie-Lena Hass and Sabine Aboling, with the University of Veterinary Medicine Hannover in Germany; and Anja These, with the German Federal Institute for Risk Assessment.

Rejection behaviour of horses for hay contaminated with meadow saffron (Colchicum autumnale L.)
Clara Mueller, Louisa Sroka, Marie-Lena Hass, Sabine Aboling, Anja These, Ingrid Vervuert
Journal of Animal Physiology and Animal Nutrition, 18 October 2021,

The study, published under a Creative Commons License, can be read here.

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