Nutritional Requirements of Rats
The brown rat has been well studied as a model species for disease in humans. This is both beneficial to our knowledge of their dietary requirements but leaves a bit to be desired. Lab block was developed to be, by nature, consistent. Consistent and affordable. The science depends on its uniformity and accessibility. We know from the science roughly what a rat needs to survive and how much of certain things are toxic. Lab block is just enough, and not too much. However, a rat's needs are dynamic and vary greatly depending on genetics, life phase and environment. We aren't raising lab rats. We want our rats to live long and thrive not merely survive.
Ethology informs us that much of any animals' behavior is shaped by the acquisition and consumption of food. Acquiring food is more than a means to survival, it's a highly ingrained behavior sequence and universally enjoyed experience. The prevailing theory that has led us to a uniform pellet, block or kibble is that an animal cannot self-select an appropriate diet and will overconsume on calorically denser ingredients leaving key nutrients behind. A nutritionally balanced extruded product was thought to be the healthier alternative.
However, research shows that rats are able to self select and will adjust nutrient intake according to their needs. (Link)
In animal behavior studies we look at the power of choice for animals that often have little bodily autonomy. Choice can be a powerful tool for positive behavior change. So too, is the choice to choose what we eat. Experiencing novel textures, smells and tastes is enriching and choosing how, when and what is eaten offers control to creatures usually afforded very little.
So what do rats eat? A little bit of everything! More specifically rats are omnivores and hind-gut fermenters. Meaning that they ferment fiber in the cecum and colon relying on the symbiotic bacteria to utilize the end products of this process. Rats can digest fibrous matter that other mammals cannot. Unlike Rabbits (who are also hind-gut fermenters) rats prefer more protein in their diet. If allowed to self-select, rats eat an average of 25% protein. Rats in coastal areas have been seen hunting fish, while those in wooded areas have been seen consuming small invertebrates or poaching eggs.
While similar in needs to other omnivores such as dogs and humans, (which are not hind gut fermenters and have a reduced ability to use excess fiber) rats do require more calcium than humans, more manganese, vitamin K and Vitamin B12. Rats have a very high metabolism and unique needs to support proper teeth and bone health. A rat's incisors are harder than iron, copper or platinum! They contain iron in the enamel making them yellow in appearance, and the pigment increases with age. Because of the rats ever growing teeth, prolonged growth period compared to lifespan and predisposition to kidney disease, it is important to maintain the proper calcium to phosphorus ratio of 1.3 to 1.