When looking for hay for a rabbit, three names come up above all: timothy, alfalfa and meadow hay. They're not interchangeable, and choosing well depends mainly on the animal's age and condition.
Timothy hay
Timothy is a grass, a fibrous hay, low in calcium and with a moderate amount of protein. That profile makes it a very suitable choice for a healthy adult rabbit: plenty of fiber for digestion and tooth wear, without excess calories or calcium.
Alfalfa
Alfalfa is a legume, considerably richer in calcium and protein. It's not what's needed for a healthy adult rabbit, because that excess favors excess weight and urinary problems. It makes sense in specific cases —growing pups, pregnant or nursing females, animals recovering from illness— and always best under veterinary guidance.
Mountain meadow hay
Meadow hay brings together many different species, a mix of grasses and legumes growing side by side in the meadow. That diversity gives a varied, balanced hay, with the fiber of grasses and an aroma animals readily accept. It's the hay closest to what a herbivore would choose to eat on its own.
Which to choose
For a healthy adult rabbit, the usual answer is a grass or meadow hay available at all times, such as high-mountain hay. Alfalfa remains the exception for specific stages or situations. If you're unsure about your rabbit's condition, your vet is best placed to advise you.
