Phosphorus works hand-in-hand with calcium to build and maintain strong bones and teeth, and it plays a vital role in energy metabolism and cell membrane integrity. For rabbits, the calcium-to-phosphorus ratio is arguably more important than the absolute amount of either mineral alone. A healthy ratio of about 1.5:1 to 2:1 (calcium to phosphorus) helps ensure that both minerals are used efficiently and that excess calcium is managed properly. When phosphorus is too low relative to calcium, more calcium gets deposited in places it should not be, like the kidneys and bladder. Phosphorus is generally well-supplied by a standard hay and greens diet.
A day's portion of timothy hay naturally provides about 150 to 250mg of phosphorus — your adult 2kg rabbit needs approximately 250 to 400mg of phosphorus per day (about 0.25 to 0.4% of the diet). Timothy hay has a naturally balanced Ca:P ratio, making it the ideal foundation for keeping both minerals in line.
0.48% of daily nutrient intake
Phosphorus makes up 0.48% of your domestic rabbit's total daily nutritional requirements by weight. That's a tiny amount — but it matters.
Poor bone development in young rabbits, weakness, reduced appetite, and impaired growth. True phosphorus deficiency is uncommon in rabbits eating a varied diet with hay and greens.
Excess phosphorus can interfere with calcium absorption and disrupt the critical Ca:P ratio, potentially weakening bones. Very high phosphorus intake is uncommon from natural foods but can occur with grain-heavy or legume-heavy diets.
| Life Stage | Size | Min | Max | Unit | Notes |
|---|---|---|---|---|---|
| Adult | — | 250 | 400 | mg | Maintain Ca:P ratio of 1.5:1 to 2:1. Timothy hay provides well-balanced phosphorus. |
Source: NRC 1977, general veterinary consensus
The calcium-to-phosphorus ratio is one of the most critical nutritional ratios for rabbits. A ratio of 1.5:1 to 2:1 (Ca:P) ensures both minerals are used efficiently for bone health and that excess calcium is minimized. An imbalanced ratio can worsen bladder sludge or weaken bones.
What this means: Feed timothy hay as the base diet — it has a naturally balanced Ca:P ratio. Avoid feeding too many high-calcium greens without corresponding phosphorus sources. If your rabbit has a history of urinary calcium issues, ask your vet about adjusting this ratio downward.
