There are a wide variety of different hay types – each with its own benefits (a few even have drawbacks) for your animals. Always consult your vet or an equine nutritionist before you decide which hays to feed your horse, as their results can vary widely from breed to breed.
A palitable hay that horses like the taste of, this is the hay often used to make cubes & pellets. Alfalfa is easy to digest & high in protein, energy, vitamins & minerals. It is also produced & sold in every state of the US.
Has been thought to cause impaction in horses when low in quality, so buyer should be very aware of the product they are purchasing. This is a good flavored hay & generally animals like the taste of it.
When dried, clover hay doesn’t preserve the green color & becomes dry looking. This is normal. Clover is often mixed with grass hay & comes in red, white, crimson, alsike & landino. *Be aware when you feed clover hay that if it becomes damp, the mold can make horses very sick.
Oat hay has thicker, tougher stalks than the other options available (which some horses won’t eat). It is a hardy hay & seems to take a while for them to eat. Can be higher in sugar – not a good option for insulin resisting animals.
Orchardgrass hay is not as sensitive to time of cutting with regards to end-stage nutrient content. While it is not as nutrient rich as alfalfa hay, it has good flavor & is high in fiber.
Fescue – both in pasture & hay form – can be damaging to pregnancy in mares. This is a long, soft hay which also yellows as it dries.
Timothy hay is easier on the digestive system than some of the others, it is high in fiber & low in calcium content. Timothy has a tendency to be more expensive, but high in nutrients for aged animals, lactating mares & growing young.
Some more in-depth reading about hay.
University of Maryland Horse Hay Quality & Selection