Hay is simply grass (or other forage plants) that has been cut and dried for animal feed. Almost any grass can become hay, but certain species are favored because they produce more nutrition, dry well, and store safely. The specific grass used depends largely on climate, the animal being fed, and when the crop is harvested.
How Grass Becomes Hay
Hay isn’t a different plant from grass. It’s grass that has been mowed at a specific growth stage, left to dry in the field (or dried mechanically), and then baled for storage. The drying process drops the moisture content low enough to prevent mold and spoilage. For small stacked bales, moisture needs to be below 20 percent before baling. Large square or round bales need to be under 18 percent. Bale hay too wet and you risk mold growth or, in extreme cases, spontaneous combustion from the heat generated by microbial activity inside the bale.
Sun-dried hay loses some nutrients compared to fresh grass, but it gains vitamin D through ultraviolet exposure, which converts natural plant sterols into the vitamin. As long as hay is stored properly and not kept too long, it retains solid nutritional value for months.
Cool-Season Grasses Used for Hay
In temperate climates, the most common hay grasses are cool-season species that thrive in spring and fall. Timothy is probably the most recognizable hay grass, especially for horse owners. It’s palatable, easy to digest, and moderate in protein, averaging around 9 percent crude protein on a dry-matter basis. Its fiber content is high, which makes it ideal for animals that need steady forage without excess calories.
Orchardgrass is another popular choice. It grows faster than timothy, tolerates shade better, and regrows quickly after cutting, so farmers can often get multiple harvests per season. Tall fescue is extremely durable and drought-tolerant, making it a workhorse hay crop across much of the United States, though some older varieties contain a fungal endophyte that can cause problems for horses and pregnant cattle. Perennial ryegrass rounds out the major cool-season options, producing fine-textured, leafy hay that animals eat readily.
Warm-Season Grasses Used for Hay
In southern and tropical regions, warm-season grasses dominate hay production. Bermudagrass (particularly the Coastal bermudagrass variety) is one of the most widely grown hay crops in the southeastern U.S. It handles heat and humidity well and can be cut multiple times during a long growing season. Bahiagrass is another warm-season staple, though it tends to be lower in nutritional quality than bermudagrass.
Summer annual forages like sudangrass, sorghum-sudan hybrids, and millets are also cut for hay. These grow fast in hot weather and can fill gaps when perennial grasses aren’t producing. They should be harvested at the boot stage, just as seedheads begin to emerge, to capture the best balance of yield and quality.
Legume Hay Is Not Grass Hay
Alfalfa is the other major hay crop, but it’s not a grass. It’s a legume, more closely related to clover and peas. The distinction matters because legume hays and grass hays have very different nutritional profiles. Alfalfa hay contains roughly 127 to 135 grams of crude protein per kilogram of dry matter, while meadow grass hay contains only about 79 to 88 grams. That makes alfalfa roughly 50 to 60 percent higher in protein.
Calcium tells a similar story. Alfalfa hay delivers around 10 grams of calcium per kilogram of dry matter, compared to about 4 to 5 grams in grass hay. Dairy cattle and high-performance animals often need that extra protein and mineral content. For horses doing light work or animals prone to weight gain, plain grass hay is usually the better fit because it provides fiber and forage time without the caloric and protein surplus.
Harvest Timing Changes Everything
The same grass field can produce very different hay depending on when it’s cut. The highest quality hay comes from grass harvested during the vegetative stage, before the plant puts energy into producing seeds. For most grasses, the ideal window is the boot stage, the brief period when seedheads are just beginning to emerge from the stem.
Once a grass plant flowers and sets seed, the stems become woodier, fiber increases, and protein drops. A field of timothy cut at boot stage might test well above 10 percent protein, while the same field cut a few weeks later in full bloom could fall below 7 percent. Farmers often face a tradeoff: cutting early means higher quality but lower total yield, while waiting produces more tonnage of less nutritious hay.
How to Spot Good Hay
You can learn a lot about hay quality before ever sending a sample to a lab. Color is the first clue. Bright green hay generally indicates it was cured under good conditions, dried quickly, and stored out of the weather. Sun-bleached hay that’s lost some green color on the outside may still be perfectly nutritious inside the bale. But hay that’s turned dark brown or black was likely baled too wet, and the discoloration signals heat damage or mold.
Smell is equally telling. Good hay smells like freshly mowed grass, clean and slightly sweet. A musty, mildewed, or sour odor means moisture got trapped in the bale. Hay baled above 20 percent moisture often develops a tobacco-like smell and brown color from internal heating. This kind of hay can harbor mold spores that are particularly dangerous for horses, whose lungs are sensitive to dust and fungal particles. Cattle tolerate dust and mild mold better than horses do, but heavily spoiled hay should be avoided for any animal.
Texture matters too. Soft, leafy hay gets eaten in greater quantities than stiff, stemmy hay. When you handle a flake, check whether the leaves are still attached to the stems or crumbling away. Leaves hold a disproportionate share of the plant’s protein and energy, so hay that’s lost its leaves during rough handling is nutritionally poorer than it looks.
Matching Hay to the Animal
Horses generally do best on clean, dust-free grass hay like timothy or orchardgrass. Their digestive systems are less forgiving than a cow’s, and they’re more susceptible to respiratory problems from moldy or dusty forage. A moderate-protein grass hay in the 8 to 12 percent range meets the needs of most adult horses at maintenance or light work.
Cattle are ruminants with a four-chambered stomach that can extract nutrients from coarser, lower-quality forage. Bermudagrass, tall fescue, and even mature grass hay that would be too stemmy for horses can work well for beef cattle. Dairy cows, on the other hand, need the higher protein and energy found in alfalfa or early-cut grass hay to support milk production. Dairy-quality alfalfa can exceed 25 percent protein, which would be far too rich for most horses.
Small animals like rabbits and guinea pigs thrive on timothy hay, which provides the long-stem fiber essential for their digestive health and helps wear down continuously growing teeth. For these pets, hay isn’t just feed. It’s the foundation of their diet, and timothy’s balance of fiber and moderate protein makes it the standard recommendation.