The cecum is a blind sac, or pouch, that comes off the junction of the small and large intestines. It is located where the appendix is in humans. The large intestine, or colon, is the section that continues from the small intestine to the anus of the animal.
The material that cannot be broken down any further, such as indigestible fiber, passes directly into the large intestine. This indigestible fiber is important in the diet of the rabbit as it helps to stimulate intestinal contractions, which keeps the chyme moving through the gastrointestinal tract.
Rabbits that do not consume enough fiber from hay are more likely to develop gastrointestinal blockages, or stasis. The material that can be broken down further, primarily soluble fiber and proteins, moves into the cecum, a large blind sac. The cecum may be the most important part of the digestive system of the rabbit. The cecum has 10 times the capacity of the stomach of the rabbit. Here massive quantities of bacteria and microorganisms reside.
These bacteria ferment, or digest, the material that passes into the cecum and use it to produce their own cells, proteins, and vitamins.
The bacteria turn the indigestible fiber into digestible nutrients — some of which are directly absorbed across the wall of the cecum for use by the animal, while others are excreted. About eight hours after a meal, the material from the cecum is packaged into a small moist pellet called a cecotrope. This allows the material to go through the entire digestive system again and let the rabbit get additional nutrients from the plant material.
This process, called cecotrophy, allows rabbits to utilize high-fiber plant material that other animals may not be able to. The diet should be high in fibrous materials to provide for proper dental health, as well as to ensure movement through the digestive system and for fermentation in the cecum to occur to produce cecotropes. This fiber should come from high-quality plant materials to allow for sufficient nutrient utilization as the passage rate in the rabbit is relatively rapid.
Choosing a high-quality pelleted diet and hay will be optimal for proper gastrointestinal health in the rabbit.
Skip to content The rabbit, as an herbivore, is uniquely designed to consume large amounts of plant material. Functions of the digestive system: It is important to consider the roles of the digestive system before looking into its parts in more detail.
Esophagus Once food is swallowed, it passes through the esophagus. Stomach Rabbits have a relatively large stomach to allow for holding of large meals because they are crepuscular, meaning they eat primarily at dawn and dusk. Small intestine The chyme passes into the small intestine from the stomach. Large intestine and cecum The final sections of the digestive system are the large intestine and cecum. Healthy microbial populations in the cecum are critical for proper digestion and optimal gut health.
Path of digestion Food travels from the stomach to the small intestine, where it encounters enzymes which aid in digestion and absorption of nutrients from proteins, sugars and starches. From there it travels to the cecum, where the microbial breakdown of fiber occurs.
It then enters the large intestine, where there is significant water resorption, followed by excretion of the feces. If the cecum occurs at the end of the digestive tract, how do the nutrients released from the fiber get absorbed? Volatile fatty acids, which are the energy component of fiber digestion, can be absorbed directly through the cecal epithelium.
We never see them because rabbits practice coprophagy — they eat these special night feces directly from the anus. Like all animals, rabbits need a balance of all the necessary nutrients in order to be optimally productive and healthy. Animals obtain their nutrition from the consumption of other organisms.
Depending on their diet, animals can be classified into the following categories: plant eaters herbivores , meat eaters carnivores , and those that eat both plants and animals omnivores. The nutrients and macromolecules present in food are not immediately accessible to the cells. There are a number of processes that modify food within the animal body in order to make the nutrients and organic molecules accessible for cellular function.
As animals evolved in complexity of form and function, their digestive systems have also evolved to accommodate their various dietary needs. Herbivores are animals whose primary food source is plant-based.
Examples of herbivores, as shown in Figure 1 include vertebrates like deer, koalas, and some bird species, as well as invertebrates such as crickets and caterpillars.
These animals have evolved digestive systems capable of handling large amounts of plant material. Herbivores can be further classified into frugivores fruit-eaters , granivores seed eaters , nectivores nectar feeders , and folivores leaf eaters. Figure 1. Herbivores, like this a mule deer and b monarch caterpillar, eat primarily plant material. Carnivores are animals that eat other animals. Obligate carnivores are those that rely entirely on animal flesh to obtain their nutrients; examples of obligate carnivores are members of the cat family, such as lions and cheetahs.
Facultative carnivores are those that also eat non-animal food in addition to animal food. Note that there is no clear line that differentiates facultative carnivores from omnivores; dogs would be considered facultative carnivores. Figure 2. Carnivores like the a lion eat primarily meat. The b ladybug is also a carnivore that consumes small insects called aphids.
Omnivores are animals that eat both plant- and animal-derived food. In Latin, omnivore means to eat everything. Humans, bears shown in Figure 3a , and chickens are example of vertebrate omnivores; invertebrate omnivores include cockroaches and crayfish shown in Figure 3b.
Figure 3. Omnivores like the a bear and b crayfish eat both plant and animal based food. Animals have evolved different types of digestive systems to aid in the digestion of the different foods they consume. The simplest example is that of a gastrovascular cavity and is found in organisms with only one opening for digestion.
Platyhelminthes flatworms , Ctenophora comb jellies , and Cnidaria coral, jelly fish, and sea anemones use this type of digestion. Ingested material enters the mouth and passes through a hollow, tubular cavity. Cells within the cavity secrete digestive enzymes that break down the food. The food particles are engulfed by the cells lining the gastrovascular cavity. The alimentary canal , shown in Figure 4b, is a more advanced system: it consists of one tube with a mouth at one end and an anus at the other.
Earthworms are an example of an animal with an alimentary canal. Once the food is ingested through the mouth, it passes through the esophagus and is stored in an organ called the crop; then it passes into the gizzard where it is churned and digested.
From the gizzard, the food passes through the intestine, the nutrients are absorbed, and the waste is eliminated as feces, called castings, through the anus. Figure 4. Vertebrates have evolved more complex digestive systems to adapt to their dietary needs.
Some animals have a single stomach, while others have multi-chambered stomachs. Birds have developed a digestive system adapted to eating unmasticated food. Humans and many animals have a monogastric digestive system as illustrated in Figure 5a and 5b. The process of digestion begins with the mouth and the intake of food. The teeth play an important role in masticating chewing or physically breaking down food into smaller particles.
The enzymes present in saliva also begin to chemically break down food. The esophagus is a long tube that connects the mouth to the stomach. Using peristalsis, or wave-like smooth muscle contractions, the muscles of the esophagus push the food towards the stomach. In order to speed up the actions of enzymes in the stomach, the stomach is an extremely acidic environment, with a pH between 1. The gastric juices, which include enzymes in the stomach, act on the food particles and continue the process of digestion.
Further breakdown of food takes place in the small intestine where enzymes produced by the liver, the small intestine, and the pancreas continue the process of digestion. The nutrients are absorbed into the blood stream across the epithelial cells lining the walls of the small intestines. The waste material travels on to the large intestine where water is absorbed and the drier waste material is compacted into feces; it is stored until it is excreted through the rectum.
Figure 5. However, in the rabbit the small intestine and cecum are enlarged to allow more time to digest plant material. The enlarged organ provides more surface area for absorption of nutrients. Rabbits digest their food twice: the first time food passes through the digestive system, it collects in the cecum, and then it passes as soft feces called cecotrophes. The rabbit re-ingests these cecotrophes to further digest them. Birds face special challenges when it comes to obtaining nutrition from food.
They do not have teeth and so their digestive system, shown in Figure 6, must be able to process un-masticated food. Birds have evolved a variety of beak types that reflect the vast variety in their diet, ranging from seeds and insects to fruits and nuts. Because most birds fly, their metabolic rates are high in order to efficiently process food and keep their body weight low. The stomach of birds has two chambers: the proventriculus , where gastric juices are produced to digest the food before it enters the stomach, and the gizzard , where the food is stored, soaked, and mechanically ground.
The undigested material forms food pellets that are sometimes regurgitated. Most of the chemical digestion and absorption happens in the intestine and the waste is excreted through the cloaca. Figure 6. The avian esophagus has a pouch, called a crop, which stores food. In the avian digestive system, food passes from the crop to the first of two stomachs, called the proventriculus, which contains digestive juices that break down food.
From the proventriculus, the food enters the second stomach, called the gizzard, which grinds food. Some birds swallow stones or grit, which are stored in the gizzard, to aid the grinding process. Birds do not have separate openings to excrete urine and feces. Instead, uric acid from the kidneys is secreted into the large intestine and combined with waste from the digestive process.
This waste is excreted through an opening called the cloaca. Birds have a highly efficient, simplified digestive system. Recent fossil evidence has shown that the evolutionary divergence of birds from other land animals was characterized by streamlining and simplifying the digestive system.
Unlike many other animals, birds do not have teeth to chew their food. In place of lips, they have sharp pointy beaks. The horny beak, lack of jaws, and the smaller tongue of the birds can be traced back to their dinosaur ancestors. The emergence of these changes seems to coincide with the inclusion of seeds in the bird diet. Seed-eating birds have beaks that are shaped for grabbing seeds and the two-compartment stomach allows for delegation of tasks.
Since birds need to remain light in order to fly, their metabolic rates are very high, which means they digest their food very quickly and need to eat often. Contrast this with the ruminants, where the digestion of plant matter takes a very long time. Ruminants are mainly herbivores like cows, sheep, and goats, whose entire diet consists of eating large amounts of roughage or fiber. They have evolved digestive systems that help them digest vast amounts of cellulose.
They use their lower teeth, tongue and lips to tear and chew their food. From the mouth, the food travels to the esophagus and on to the stomach. To help digest the large amount of plant material, the stomach of the ruminants is a multi-chambered organ, as illustrated in Figure 7. The four compartments of the stomach are called the rumen, reticulum, omasum, and abomasum.
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