Which characteristic does Laburnum possess that is harmful to horses?

Laburnum is known to possess toxic seeds and foliage, making it harmful to horses. The plant contains alkaloids such as cytisine, which can be dangerous if ingested by horses. Even small amounts of the leaves or seeds can cause severe symptoms, including gastrointestinal distress and respiratory failure. This toxicity is a crucial reason why horse owners must be cautious about the plants available in pastures or around horse facilities.

The sugar content or supposed benefits to digestion and coat condition mentioned in the other choices do not accurately reflect the nature of Laburnum. The sugar content in flowers is not a known characteristic of Laburnum that would impact horses negatively, nor is it recognized for any beneficial digestive properties or enhancements to coat condition. Therefore, recognizing Laburnum's toxicity helps ensure the safety and health of horses in environments where this plant might be present.