It is important to understand how nutrients like carbohydrates, proteins, fats, amino acids and fibre affect your rabbit’s health.
Let’s start at the start…
The table below provides details on how much of the given nutrients are required in a rabbit’s diet per day.
Most of these are fulfilled with a proper diet of grass, hay, pellets and salad greens.
| Nutrient | Recommended Level (adult) | Recommended Level (growing, pregnant, nursing) | Description |
|---|---|---|---|
| Protein | 12% – 16% | 16% – 20% | Vary at different life stages. Younger rabbits need the same amount of protein as nursing does. Higher amounts are detrimental to long-term health. |
| Carbohydrate | 20% – 27% | 15% – 25% | Major source of energy. Usually in the form of fibre. |
| Fibre | 43% – 47% | 44% – 50% | Fibre is the most important nutrient. |
| Fat | 2% – 3.5% | 3% – 5.5% | Used for energy and to absorb fat-soluble vitamins. Excessive intake can cause obesity, hepatic lipidosis and atherosclerosis in the aorta. |
| Ash | 4% – 6.5% | 4.5% – 6.5% | Vitamins and minerals are important, should include limestone, vitamin C, or mineral premix. Salt should be max. 0.2%. |
Nutrient list
This table breaks down each vitamin, mineral and nutrient into the required amounts for a rabbit’s daily diet.
| Nutrient | Recommended daily allowance per 100g of feed for > 6 months (adult) | Recommended daily allowance per 100g of feed for < 6 months (growing) | ||
|---|---|---|---|---|
| Minimum | Maximum | Minimum | Maximum | |
| Crude Fibre | 140 | 250 | 140 | 160 |
| Fat | 25 | 50 | 30 | 50 |
| Starch | Nil | 200 | Nil | 135 |
| Protein | 120 | 170 | 150 | 180 |
| Macro-minerals | ||||
| Calcium | Nil | 5 | Nil | 5 |
| Phosphorus | Nil | 4 | Nil | 4 |
| Ca / P ratio | 2:1 | 2:1 | ||
| Sodium | 1 | 2 | 1 | 2 |
| Magnesium | 0.3 | 3 | 0.4 | 0.7 |
| Potassium | Nil | 6 | 2 | 6 |
| Chloride | Nil | 1.7 | 1 | 5 |
| Micro-minerals | ||||
| Copper | 0.005 | 0.02 | 0.003 | 0.006 |
| Zinc | 0.05 | 0.15 | Nil | 0.04 |
| Manganese | 0.008 | 0.015 | 0.20 | 0.40 |
| Iron | 0.03 | 0.4 | 0.1 | Nil |
| Iodine | 0.0004 | 0.0005 | Nil | Nil |
| Selenium | 0.00005 | 0.00032 | 0.0001 | Nil |
| Cobalt | Nil | 0.00025 | 0.0001 | 0.001 |
| Vitamins – fat soluble | ||||
| Vitamin A | 0.010 | 0.012 | 0.006 | 0.01 |
| Vitamin D | 0.0008 | 0.001 | 0.0005 | Nil |
| Vitamin E | 0.05 | 0.16 | 0.05 | Nil |
| Vitamin K | 0.001 | 0.002 | Nil | Nil |
| Vitamins – water soluble | ||||
| Vitamin B Complex | Not required as body makes it | |||
| Vitamin C | Not required as body makes it | |||
| Vitamin E | Vitamin E and C must be the same levels | |||
Protein and Amino Acids
Rabbits require quality protein to maintain a healthy diet. When rabbits are growing they rely on having substantial quantities of dietary essential amino acids; however, them proteins re-digested in thee cecum does not make a large contribution to the essential amino acid needs of the young rabbit. Poor quality proteins like zein and gelatin do not support normal growth. Studies showed that rabbits that had a diet with a no or low protein diet did not grow as much as other rabbits.
Amino acids help bunnies grow. Arginine is essential for growth, methionine and lysine are also vitally important. According to several studies, arginine at 0.6%, lysine at 0.65% and sulfur amino acids (methionine and cystine) at 0.6% supported a rapid growth rate in young rabbits of 35-40g a day.
Rabbits are able to get protein efficiently out of plants. As an example, when eating alfalfa, pigs could get less than 50% of protein from it, while rabbits get about 75%. That is why they like feeding rabbits alfalfa/lucerne, because it helps them put on weight as they are growing. If a growing rabbit is given a diet that consisted of about 10-60% alfalfa, they had a growth rate of about 34g a day. While a diet of 90% alfalfa put on only 23g a day. That means a diet with a lot of alfalfa/lucerne is not necessarily a good thing.
Protein
Rabbits can digest protein quite well and microbial protein plays a minor role in meeting the bunny’s amino acid and protein requirements. Low protein diets increase caecotrophy, where as high levels decrease caecotrophy.
What are proteins and amino acids?
Proteins are macromolecules that are made of long chains of amino acid residues that are linked together by peptide bonds, together they form polypeptide chains.
The properties of each amino acid depend on the structure of its chain, determined by the size and electric charge. There are 8 amino acids that are essential for proper nutrition:
- isoleucine
- leucine
- lysine
- methionine
- phenylalanine
- threonine
- trytophan
- valine
Proteins are considered nutritional when they have the right amino acid composition and they allow the gut to absorb the amino acids.
If the chemical structure of the proteins is wrong, they become non-digestible and more resistant to being absorbed, which makes them resistant to enzyme activity.
Plant proteins are divided into two major groups:
- seeds
- leaf
Seeds have an endosperm (the main large squishy part that is the food for the germ), the germ (where the plant comes from) and the shell (or bran). The average endosperm has about 0.7% of protein in it. The germ and bran have the remainder.
When rabbits are fed cereals, like wheat, barley, oats, maize, beans, peas, or soy, they will only get about 0.13 of their daily crude protein. Proteins are different between cereals, and are put into two categories:
- soluble – albumins and globulins
- insoluble – prolamins and glutelins
The grain of legumes and the oils in the seeds contain much more soluble protein than cereal grains. Legume proteins are richer in essential amino acids (especially lysine) and should be more digestible than than cereals.
When unprocessed, seeds can have anti-nutritive factors that inhibit absorption of amino acids and may even contain tannins and lectins.
Lectins are plant proteins that bind to certain sugars and cause agglutination in some cells.
Agglutination is the clumping of cells.
Tannins is organic bitter-tasting yellowish or brownish chemical that is found in some plant tissues. Consists of gallic acid, which is used as a colouring dye, and is found in tea.
Rabbit diets that include soybean or sunflower meals, have concentrated protein levels and can make up between 3.5-4% of the daily dietary protein.
Plants have concentrated proteins in the leaves, unlike grains, where they are concerned with the growth and biochemical functions of the cells. If a rabbit’s diet is 90% lucerne hay, it is getting 25% of it’s daily dietary protein from it, but that only matters if it is good quality lucerne hay.
Protein and Amino Acid Balance
It is important to feed foods to your bunny that meet the protein and amino acid requirements. That depends on which nitrogen unit was used, crude protein (albumins and globulins) and methionine (prolamins and glutelins).
These two graphs show the value of different foods and their nitrogen unit.
To understand these graphs, think of 100 as 100%. The blue Soybean meal is regarded as 100% protein, and other foods are compared to it.
The first graph, is calculated to show crude protein, while the second graph shows methionine. Crude protein and amino acids are the most common way to show nitrogen and nutritional values of foodstuffs.
That means sunflower meal has 80% of the protein that soybean meal does if using the crude protein scale, and it has 140% of the protein soybean does if using the methionine scale.
When choosing dry foods, you have to be certain of the scale they are using to calculate the protein, because manufacturers could be using either scale.
It can get confusing, very quickly.
Nitrogen Metabolism in the Caecum
When food travels through the digestive system, it is broken down to get nutrients from it. Certain chemicals and urea are recycled through the blood which allow caecal bacteria to get energy and nitrogen for growth. There is about 70% of total dry matter left when food gets to the end of the ileum, but keep in mind that it is made up of about 30% digestible fibre (no need to pass it through the caecum) and about 15% nitrogen residues.
The caecum has more ammonia and true protein (enriched by essential amino acids), and it ferments nitrogen up to 91%. Left over nitrogen is cycled through the blood and then if there is any left, it is passed through urine.
Caecotrophs and Protein Digestion
Rabbits eat their caecotrophs to obtain protein from it. The mucous layer that covers the caecotroph contains nitrogen, and that nitrogen can be up to 0.05g a day, if the rabbit is making 20g of caecotrophs a day. Rabbits can redigest about 18% of the crude protein from a caecotroph.
Starch and Sugar
Here’s an infographic about carbohydrates!
Having a high-fibre diet usually causes food to be incompletely digested in the small intestine because it has a fast gastrointestinal transit time. This means that the incomplete chemical digestion makes starch available to organisms in the hindgut. This can cause microbes to grow exponentially, create a carbohydrate overload and lead to enteritis or possible death.
Grains and feeds high in starch and sugar are not recommended. If grains are fed, they should be coarsely ground and contain low energy – oats are preferred more than corn or wheat.
Simple Sugars and Oligosaccharides
Sugars and starch are carbohydrates and are classified under a simple term: the sugars. But in science they are kept separate because they are not digested the same.
- Oligosaccharides are hydrolised by bacterial enzymes.
- Sugars are hydrolised, really quickly, by enzymes and absorbed by the intestinal mucosa.
Hydrolised is the splitting of a chemical compound into two or more new compounds by reacting to water.
In animal feed, sugars are generally at low concentrations, although sucrose can reach 500g/kg, especially in molasses.
Oligosaccharides are defined as molecules with little ability to polymerise and are not digestible by the fermentation enzymes. Oligosaccharides are mainly found in legume seeds.
Polymerise is when small molecules combine chemically together to produce a large chain or network molecule.
Starch is the second most abundant carbohydrate in nature. Cellulose is number one. In nature starch is found as granules in either seeds, roots or tubers. The shape of the starch depends on the plant as many different sizes and shapes can be found, from tiny granules in oats and rice (5-6μm), and larger granules in bananas (38-50μm).
Starch is almost completely digested in rabbits in the small intestine, usually around 0.02% of the intake will pass through to the large intestine to be digested further, although depending on the age of the bunny or the food, it can reach 10% of the intake.
According to a study conducted between 1995 to 2019, it was found that starch did not affect the mortality of young rabbits, from the time they start eating food until they are completely weaned. Starch is passed from the doe to the baby through the milk, and it is an important part of nutritional intake and contributes to health protection. When baby rabbits were weaned at 28 days of age, they passed away during week 6 of age due tot he lack of nutritional value in the feed. When babies were suckling until 42 days old, the mortality rate increased during 8 weeks of age. That is because feed is not manufactured to suit the needs of young rabbits in this situation.
Growing rabbits are more likely to get digestive problems after weaning due to the amount of physiological changes that happen during that time. It is suggested that an overload of carbohydrates that can be fermented quickly in the large intestine, increases he risk of digestive disorders in weaned rabbits. Some studies suggest that to lower the mortality rate, reduce the amount of starch and provide enzymic supplements containing amylase, which will reduce the starch in the ileum. Another study says that amylase had no effect on mortality rates, rather it depends on the source of the starch. It has been shown that digestive health was increased and mortality was decreased by increasing the amount of fibre in the diet.
Digestive issues in adult rabbits is very limited if kept within the usual dietary starch levels.
Carbohydrates
When looking at a Nutrition Analysis panel on the back of feed, the fibre fraction is the structural carbohydrates of the plant material. In the past, it was measured as crude fibre. Recently, the terms cell wall constituents (CWC) and acid-detergent fibre (ADF) have become used.
CWC consists of hemicellulose, cellulose, lignin and silica.
ADF consists of cellulose, lignin and silica.
There aren’t many ADF and CWC calculations available for rabbits as on the back of feeds it is still shown as crude fibre.
Despite the fact that crude fibre is not a sufficient energy for rabbits, dietary fibre has beneficial effects. Non-digestible fibre is necessary for a normal functioning digestive tract. Crude fibre levels less than 12% promotes diarrhoea.