Grass
Any pasture on which horses graze should be well managed and free from poisonous plants.
Grass clippings should not be fed as they can cause digestive disturbances, serious gas or impaction colic.
Hay
Hay is dried grass and any hay fed should be green and free from dust and mould as dusty hay can cause respiratory problems and mouldy hay may cause colic. Bales of hay can be checked for colour - although the exterior may be bleached by the sun, check the inside of the bale for colour. Bales can be checked for mould by placing a hand into the centre of the bale to ensure it is not warm, checking for areas of dark discolouration and by smell (hay should smell like freshly mown grass).
Slices of hay can be shook apart before feeding to shake out dust. Alternatively hay can be soaked to remove dust, although soaking hay also reduces its nutritional value. Steaming hay kills fungal spores, dust mites and bacteria without the loss of nutritional value that occurs during soaking.
If hay is to be stored outside it should be kept dry by keeping it off the ground and thoroughly covered in waterproof material.