Why Rabbits Need Unlimited Hay (And What Happens to Their Teeth Without It)

A rabbit's teeth never stop growing. Under normal conditions they grow about a centimeter a month, and an incisor with nothing opposite it to wear against can grow as much as a millimeter a day. The only thing that keeps pace is chewing, and the only food a rabbit chews long and hard enough is hay. That is why hay is the diet rather than a side dish: 80 to 85 percent of what a rabbit eats, available all day, every day.

What hay does to the teeth

All of a rabbit's teeth are open-rooted, the incisors at the front and the cheek teeth behind them that do the grinding. Eating hay takes long stretches of rapid, repetitive chewing, and that grinding is what wears the teeth down as fast as they grow.

Pellets do not do the same job. They are concentrated food that does not provide the wear hay does, and a rabbit that fills up on them eats less hay. Veterinary guidance names a diet lacking fiber as a main cause of dental disease in rabbits, alongside heredity: dwarf and lop-eared breeds are overrepresented.

When wear falls behind growth, the teeth overgrow and stop meeting properly, and the damage spreads to mouth sores and abscesses. The signs are drooling, difficulty eating, dropping food, weight loss, mouth sores, and pawing at the mouth. Treatment means skull X-rays and trimming the teeth under anesthesia with proper rotary tools, often every 4 to 12 weeks for the rest of the rabbit's life, and in severe cases extraction. None of that can be undone by switching to hay later, which is why prevention is the whole game.

The same open-rooted design is why hay is the staple for other small herbivores too: guinea pigs and chinchillas get dental disease from the same shortfall.

What hay does to the gut

A rabbit's digestive tract depends on a steady flow of fiber to keep moving. Hay keeps the cecum, the fermentation chamber where gut bacteria break down plant material, in balance, and it keeps food moving through. When fiber drops, gut movement slows, the cecal bacteria shift, and the rabbit can stop eating. A rabbit that stops eating or produces fewer droppings needs a vet that day.

Measuring the pellets rather than filling the bowl has a second benefit: it makes a drop in appetite obvious the day it happens.

How much, and which hay

The practical rule is unlimited grass hay, with a rabbit-sized bundle as a rough guide to what one rabbit eats in a day. The rest of the diet is small:

Grass hays suit adults because they are lower in protein and calcium than legume hay. Timothy and orchard grass are the common ones, and bluegrass, brome, fescue, oat and ryegrass hays also work. Mixing types keeps a picky rabbit eating. Alfalfa is a legume hay with too much calcium and protein for a mature rabbit, and it is reserved for young rabbits under about six months and for nursing does.

If I were cutting anything from a rabbit's budget, it would never be the hay. Every other part of the diet can be adjusted later. Teeth that have already overgrown for want of it cannot.

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