Final answer:
Calcium is the main mineral secreted in rabbit urine at a higher percentage than average mammal urine. Aldosterone helps regulate calcium concentration in urine.
Step-by-step explanation:
The mineral that is mainly secreted in rabbit urine at 45-60% more than the average mammal urine is calcium.
Calcium is excreted in the urine but only a small amount is actually filtered by the kidneys and appears in the urine. The remaining calcium is absorbed by the body or excreted through other means like feces or sweat.
Aldosterone, a hormone secreted by the kidneys, helps regulate the concentration of calcium in urine.