Fiber is the single most important nutrient in your rabbit's entire diet — and it is not even close. Rabbits are hindgut fermenters with a specialized organ called the cecum, where billions of beneficial bacteria break down plant fiber into volatile fatty acids that provide the majority of your rabbit's energy. This fermentation process is the engine that powers everything else in a rabbit's body. Without a constant supply of long-strand fiber (primarily from hay), the cecum's bacterial population collapses, gut motility slows, and the entire digestive system can grind to a halt — a condition called GI stasis that can kill a rabbit within 24 to 48 hours. Fiber also plays a critical role in dental health: a rabbit's teeth grow continuously at a rate of about 2 to 3 millimeters per week, and the lateral grinding motion required to chew hay is the only thing that keeps those teeth worn to a healthy length. Pellets and soft vegetables do not provide the same abrasive action. This is why veterinarians and experienced rabbit keepers will tell you the same thing: unlimited timothy hay, available around the clock, is the absolute foundation of rabbit nutrition. Everything else — pellets, greens, treats — is supplementary to that hay pile.
Your rabbit should eat a body-sized pile of timothy hay every single day — that is roughly 80 to 120 grams for a standard 2kg rabbit, providing about 25 to 30 grams of crude fiber. Think of it as a haystack roughly the same size as your rabbit. Hay should make up at least 80% of the total diet. Timothy hay, orchard grass, and meadow hay are ideal for adults; alfalfa hay is reserved for growing kits under 6 months and pregnant or nursing does because of its higher calcium and calorie content.
29.45% of daily nutrient intake
Fiber makes up 29.45% of your domestic rabbit's total daily nutritional requirements by weight.
GI stasis is the most dangerous and common result — your rabbit stops eating, produces small or no droppings, sits hunched and still, and may grind their teeth in pain. You may also notice soft, mushy, or misshapen cecotropes (the special nutrient-rich droppings rabbits re-ingest), dental overgrowth leading to drooling and difficulty eating, chronic soft stools or diarrhea, bloating, and a generally dull or lethargic demeanor. GI stasis is a veterinary emergency.
Excess fiber from hay is essentially impossible in a healthy rabbit — their digestive system is specifically designed to handle enormous quantities of plant fiber. A rabbit eating too much hay is not a real scenario. The only concern would be a diet of exclusively hay with zero fresh greens, which could lead to mild deficiencies in other nutrients over time, but the hay itself will not cause harm.
| Life Stage | Size | Min | Max | Unit | Notes |
|---|---|---|---|---|---|
| Adult | — | 20 | 30 | % of diet | Crude fiber should be at minimum 20% of total diet dry matter. Unlimited timothy hay is the foundation — 80% or more of the diet. |
| Juvenile | — | 18 | 25 | % of diet | Growing kits need slightly less fiber percentage as they eat more calorie-dense alfalfa hay and pellets, but hay should still be unlimited. |
| Pregnant / Nursing | — | 15 | 25 | % of diet | Pregnant and nursing does need more calories and protein, so fiber percentage may be slightly lower, but hay should still be available unlimited. |
| Senior | — | 20 | 30 | % of diet | Senior rabbits need the same high-fiber diet as adults. Hay remains essential for gut motility and dental health. |
Source: NRC 1977, general veterinary consensus
The fiber-to-protein ratio is critical for rabbit digestive health. A high-fiber, moderate-protein diet supports healthy cecal fermentation, while a low-fiber, high-protein diet can cause cecal dysbiosis, obesity, and GI problems.
What this means: Adult rabbits need a diet that is roughly 20-30% fiber and 12-14% protein. Timothy hay provides the ideal ratio. Avoid alfalfa-based feeds for healthy adults, as they are too protein-rich and tip this balance unfavorably.
