Metabolic Bone Disease in Squirrels
Metabolic bone disease, or MBD, is usually a preventable problem that can occur with captive squirrels that are not eating well (are sick) or are eating an improper diet - such as one limited to seeds, nuts, and corn – all foods that are high in phosphorous and low in calcium.
The squirrel's body needs phosphorous, but in the right proportion to calcium. When the ratio is too high in phosphorus and too low in calcium, the phosphorus blocks the absorption of calcium – resulting in MBD. Unfortunately, Squirrels LOVE nuts, seeds, and corn and will eat them exclusively like candy if given the choice.
Squirrels can be just like small children, who might prefer to live off of cookies, candy and sugary drinks – but must be encouraged to eat a balanced diet. You must not give them this choice! Since MBD can get started in less than a week, any animal that is not eating needs to be watched.
Beginning signs of disease can be subtle such as aggressiveness, excessive sleeping, reluctance to move (lethargy), reduced appetite, or labored breathing. It’s a painful disease so watch for any signs of discomfort! As the disease progresses, the squirrel may experience seizures, swollen joints, improper bone growth, paralysis and fractures.
If caught early, MBD can be treated through correcting the diet by ensuring access to foods with the correct calcium to phosphorus ratio or adding additional calcium, along with providing access to natural sunlight or full spectrum lighting.
Vitamin D Supplementation should only be done under the supervision of veterinarian. Vitamin D is a fat soluble and can build up, quickly becoming toxic.
The squirrel's diet should be composed of 80% balanced squirrel or quality rodent block and 20% fruits and vegetables with the proper Ca/pH ratios (ideally 2:1, reference the 'Calcium Rich Foods' link).
Sunlight & Vitamin D
MBD is most often caused by improper diet that does not include sufficient Calcium and Vitamin D. Vitamin D is naturally produced in response to sunlight and is essential to absorb calcium. If the squirrel does not have access to at least twenty minutes per day of unfiltered sunlight, it’s body cannot produce the Vitamin D it needs, which impedes calcium absorption. If you cannot provide a safe outside enclosure for ‘sunning,’ then either supplementation or all/full spectrum bulbs can be used.
Supplementation with Vitamin D must be done with care since too much vitamin D will kill squirrels. Supplement using drops formulated for rats or other small animals and closely follow directions. If you are feeding the squirrel 80% quality rodent block and a variety of fruits and vegetables, supplementation should be unnecessary.
Understanding the Ca to P Ratio
Calcium, combined with phosphate, forms hydroxylapatite, which is the mineral portion of bones and teeth needed to sustain life in mammals. For every milligram of phosphorus consumed, another milligram of calcium must be present or it will be pulled from existing calcium reserves in the body, such as teeth and bones. In other words for every part phosphorus present, there must be calcium and if it's not provided in the food, it will be pulled from the bones .