Deadly Nightshade is also known as Belladonna which means ‘beautiful lady’. This name comes from one of its active ingredients, Atropine, which causes dilation of the pupil but also sometimes death if the lady wasn’t careful with the dosing!
All parts of the plant, but especially the berries, are toxic to many mammals including dogs and horses. Cattle are thought to be less susceptible to toxicity than some animals but if they eat enough, signs include bloat, dilated pupils, laboured breathing and a weak pulse progressing to paralysis and death.
If a cow were to survive a bout of poisoning, her milk would be contaminated and therefore unfit for human consumption.