Small Mammal Nutrition Calculator

How Small Mammal Nutrition Works

Small mammals span a wide range of species with very different digestive systems, so there is no single diet that fits them all. Rabbits and guinea pigs are hindgut fermenters that depend on a constant supply of grass hay to keep their gut moving and their continuously growing teeth worn down. Hamsters, gerbils, and mice are omnivores that thrive on a seed and grain based mix supplemented with small amounts of fresh produce and protein. Understanding which category your pet falls into is the first step toward feeding it correctly.

Our calculator estimates daily calorie needs using your animal's species, body weight, life stage, and activity level. It applies a resting energy requirement formula and then adjusts for the factors that raise or lower a small mammal's metabolism, giving you a realistic starting point for portioning food each day.

Daily Diet Composition by Species

The table below outlines the typical diet balance for the most common small mammals kept as pets. Use it alongside your calculator results to decide how the daily calories should be split across hay, pellets, and fresh foods.

Key Nutrients Every Small Mammal Needs

Beyond calories, small mammals need the right balance of specific nutrients to stay healthy. Getting these right prevents the most common diet related illnesses seen in pet rodents and rabbits:

• Fiber: The single most important nutrient for rabbits and guinea pigs. Long strand fiber from hay keeps the digestive tract moving and prevents deadly gut stasis.
• Protein: Omnivores like rats, mice, and hamsters need moderate protein for muscle and coat health, while herbivores need far less.
• Vitamin C: Essential for guinea pigs, which cannot synthesize it and will develop scurvy without a daily dietary source.
• Calcium: Needed for bone and tooth health, but excess calcium can cause bladder stones in rabbits, so leafy greens should be rotated carefully.
• Limited fat and sugar: Most small mammals gain weight quickly, so treats, seeds, and sugary fruits should stay a small fraction of the diet.

How Life Stage and Activity Change Calorie Needs

A growing juvenile, a pregnant or nursing female, and a sedentary senior all have very different energy requirements even at the same body weight. Young, growing animals and nursing mothers may need 25 to 50 percent more calories than a resting adult, which is why alfalfa hay (higher in protein and calcium) is often recommended for young rabbits and guinea pigs before switching to grass hay in adulthood.

Activity level matters too. A rabbit with free run of a room burns considerably more energy than one confined to a hutch, and an exercise wheel raises a hamster's daily needs. The calculator lets you select an activity level so the estimate reflects your pet's real lifestyle rather than a one size fits all number.

Example: Feeding a 2 kg Adult Rabbit

Consider a healthy, moderately active adult rabbit weighing about 2 kg (roughly 4.4 lbs). Its diet should be built around unlimited grass hay, which makes up the vast majority of daily intake and provides the fiber needed to keep its gut healthy. On top of that, a rabbit this size typically receives around one packed cup of fresh leafy greens per day and only about 1/8 to 1/4 cup of quality pellets, kept small deliberately to avoid excess calories.

Entering 2 kg, the rabbit species, adult life stage, and a moderate activity level into the calculator above returns an estimated daily calorie target you can use to fine tune pellet and treat portions. Re-check the estimate if your rabbit gains or loses weight, since body condition is the best real world signal that portions need adjusting.

Common Small Mammal Feeding Mistakes to Avoid

Many small mammal health problems trace back to a handful of avoidable feeding errors:

• Too many pellets or seed mixes: These are calorie dense and encourage selective feeding, where a pet picks out the tasty high fat pieces and leaves the balanced portions behind.
• Not enough hay: Skimping on hay is the leading cause of dental disease and gut stasis in rabbits and guinea pigs.
• Sugary fruit as a daily food: Fruit should be an occasional treat, not a staple, because the sugar disrupts gut bacteria and adds unnecessary calories.
• Sudden diet changes: Switching foods abruptly can trigger digestive upset. Transition new foods gradually over a week or more.
• Ignoring body condition: Weigh your pet regularly, since small animals hide weight changes under fur and a scale catches problems early.