Ha. I assume the horses would have gotten pretty sick by eating the oleanders?
Still wouldn’t want to seriously harm the horse because of some jack-wad.
They would have died if they ate it.
Toxicity
Nerium oleander has historically been considered a poisonous plant based on a number of its compounds that may exhibit toxicity, especially to animals, when consumed in high amounts. Among these compounds are oleandrin and oleandrigenin, known as “cardiac glycosides” which are known to have a narrow therapeutic index and can be toxic when ingested.