Consider it a small-animal superfood—at least for rabbits, guinea pigs and chinchillas. Grass hay is, and should be, the core component of these animals’ diets. Although there are pellets on the market for these herbivores, they are best served by well-portioned servings of hay, with pellets being mostly supplemental.
Knowing the nitty-gritty of these animals’ digestive functions is key to understanding why hay needs to be on their menus.
Most people know that rabbits, guinea pigs and chinchillas only eat plants, but there is much more to their specialized digestive systems than most people realize. The most important fact is that they are designed to eat a lot of fiber. The first evidence of this is in their molars, which grow constantly. If they didn’t, the tough fiber in their diets would quickly wear away their teeth.
After the food is chewed and swallowed, it passes through the stomach and small intestines, and then reaches the next specialization: the cecum. A large sack attached where the small and large intestines meet, the cecum is the equivalent to our appendix. But unlike our tiny appendix, the cecum is so large it takes up most of the space in the abdomen. This is where much of the actual digestion occurs. The cecum contains special bacteria and other microorganisms to help digest fiber that mammals cannot digest themselves. Because of this, these herbivorous rodents are called “hindgut fermenters.”
Another specialized feature of their digestion is the production of pellets called cecotropes, which pass out of the anus and are eaten by the animals. Although this sounds gross, the cecotropes act like the cud of a cow, allowing the food to pass through the system a second time for better absorption of nutrients. The cecotropes are passed mostly at night, and most owners of these pets never know they exist. This has led to their common name of “night feces,” but they are very different than the animals’ normal feces.
Because the digestive tracts of these animals are designed to process a lot of fiber, it is important that they eat lots of it. Fiber keeps the digestive system working normally, effectively moving food through the digestive tract. A lack of fiber can cause sluggish digestion, resulting in bloating, gastric stasis and cecal impaction leading to enteritis, a potentially fatal bacterial infection of the intestines.
In rabbits, a low-fiber diet can also contribute to the formation of hairballs from the fur they ingest while grooming, which can cause blockages. A fiber-riche diet maintains the proper balance of bacteria in the cecum and large intestines. If the diet contains too many starches or sugars, such as those found in grains or fruit, it can upset the balance of these bacteria and result in enteritis.
Lots of fiber is also required to keep small animals’ molars from overgrowing. Overgrown molars can damage the inside of the mouth, causing pain, difficulty eating, slobbering or drooling and weight loss.
Grass is Good
Rabbits and guinea pigs also have a unique way of metabolizing calcium that is different than other animals, including chinchillas. These animals absorb all the calcium in their food and then excrete excess amounts in their urine. It is this excreted calcium that makes the urine of rabbits and guinea pigs appear cloudy.
The kidneys of rabbits and guinea pigs have to work extra hard to filter out excess calcium, so it’s important that they do not get too much calcium in their diet. Excess amounts of protein in the diet also require their kidneys to work harder. A diet too high in calcium and protein can result in kidney failure and death.
Fortunately, there is a very simple way to make sure the digestive tracts of these herbivores function properly to keep them healthy: feed them free-choice grass hay. Grass hay has the proper amount of fiber to keep digestion healthy. It is also low in calcium and protein.
In comparison, alfalfa hay—which is a legume (a plant in the bean family), not grass—is high in both calcium and protein, and therefore should be fed to adult guinea pigs and rabbits in small amounts as a treat only. Growing rabbits and guinea pigs can have more alfalfa hay in their diets.
The importance of giving grass hay free-choice to all the rodent herbivores cannot be emphasized enough. It is almost impossible for these herbivores to have too much fiber in their diet. Retailers need to pass this knowledge on to their customers who own rabbits, guinea pigs, chinchillas and other small herbivores. Grass hay should be the main diet of these animals, and pellets should be considered a supplement. This one rule of husbandry will help to prevent these serious health problems and go a long way toward keeping these pets healthy.
Debbie Ducommun has a B.A. in animal behavior and has worked in the animal field since 1982. She is the author of the book Rats!, the booklet Rat Health Care and, her most recent book, The Complete Guide to Rat Training: Tricks and Games for Rat Fun and Fitness.