The question are daffodils poisonous to horses? Poses a serious problem to horse owners. If left to over graze an area, horses are potentially placed at risk of serious illness. The problem is you have no idea what grew on the land in the dim and distant past.
On the surface its just grazing, but amongst the roots there could be lurking a dangerous poison. Bulbs could be lying dormant for many years, possibly buried too deep to produce flowers. Not yet rotted away, these bulbs can be, depending on the plant… Poisonous.
Common Questions Related to Horses and Daffodils
Yes. Daffodils can make horses seriously ill. They contain a compound called lycorine, an emetic that can cause problems with the nervous system, heart related issues, and gastrointestinal problems.
They also contain calcium oxalate which can cause kidney complications. This applies to all types of daffodils including narcissus, jonquil, and paper whites.
Signs to look for include, dehydration, diarrhoea, convulsions, abdominal discomfort, seizures, excessive salivation, tremors, low blood pressure, abnormal heart rate, sensitivity to sunlight, or skin inflammation. 
Keep an eye on the animal, remove any sources of daffodil from the animals living area. Most horses will not eat daffodils through choice, it is more likely that they come into contact accidentally or because of a lack of fresh food.
Contact your vet and seek their advice, if possible show the vet the daffodil. Either in part or ideally the whole plant bulb included.
All of the daffodil is poisonous, the most dangerous part is the bulb but the roots, leaves, stalks, flowers and even the dust from the skin of the bulb is also harmful to horses.
Depending on the amount consumed and the size of the horse, daffodil poisoning is not usually fatal. Your horse will suffer serious discomfort but should recover. Horses can come into contact with daffodils accidentally and this will usually lead to inflammation of the skin.
Prevention is Better Than Cure
Never allow your horses to come into contact with any part of the daffodil. Make sure they have an adequately varied diet, with enough greenery, and if they are accidentally exposed to daffodils contact your vet at once. If they have enough variety in their diet they won’t need to go grubbing through the soil looking for food.
If possible don’t exercise your horse in an area where you know daffodils are growing. they are a lovely welcome to Spring but daffodils and horses should be kept separate at all times.