Alfalfa hay and timothy hay are different nutritionally
Alfalfa hay and timothy hay are both forage sources commonly used in rabbit and guinea pig diets. Nutritionally speaking, however, they are very different. Alfalfa contains higher concentrations of protein and calcium compared to timothy hay (Table 1). When alfalfa or timothy is used in a complete rabbit feed, the nutrients of the hay source used is taken into account and mixed with other appropriate ingredients to obtain a final diet formula that meets the needs of rabbits or guinea pigs. For example, while calcium is much higher in alfalfa than in timothy, in a complete feed, the amount of additional calcium sources (such as calcium carbonate) would be lower in an alfalfa-based diet compared to a timothy-based formula.
Rabbits and calcium
Calcium metabolism in rabbits is unique compared to other species. Rabbits are efficient calcium absorbers and excrete excess calcium in their urine. For this reason, rabbit urine may leave a white, chalky residue. Because of this unique metabolic system, rabbits are prone to urinary stones if fed too much calcium. Therefore, when feeding an adult rabbit supplemental hay in addition to a complete diet, it is preferable to provide timothy hay to minimize excess calcium.