With so many feed options out there for rabbits, it can be hard to sort through them and find what is truly best for the health of our animals. Many sources will recommend a diet of mostly hay (such as the House Rabbit Society recommending it be 80% of their diet and others even recommending 90%) without citing any scientific basis for the nutritive value of their claims. This type of information gets repeated widely in the rabbit community, ending up in countless articles with continued lack of evaluation of actual nutritional benefit. "A rabbit's diet should be mostly Timothy hay" is so widely said that it is considered common knowledge to many, but my hope with this article is to prove why it is flawed.
To preface this article, I want to acknowledge that nutrition in general is such a broad topic with many different strong opinions out there on what is best and what is bad. Imagine asking 10 random people what the ideal diet for humans is - you will get 10 different answers and many will contradict each other! It is the same in the rabbit world and I want to emphasize that this entire article is centered around making sure we are providing a diet that meets nutritional requirements, not what specific foods should be fed to meet them with. This article is not saying that hay is bad, but simply asking the reader to possibly think about hay differently in how it nourishes their rabbits.
Nutritional Requirements for Age and Productive Status
There is no one-size-fits-all diet for rabbits with nutritional requirements varying by stage of life and production (see table below). There are certainly other factors impacting nutritional requirements with one example being Angora breeds commonly fed a higher protein feed to support fiber growth (Lebas et al. 2010), so other considerations such as that will impact how to balance the rabbit's diet beyond general recommendations.
Below is a simple table including some of the main nutritional considerations (see sources for more expansive list) for four main stages of life and production. Included are the recommendations by the National Research Council (NRC) for rabbits in addition to work done by F. Lebas who reported slightly higher nutritional requirements in many situations.
|
|
|
Growth |
Maintenance |
Gestation |
Lactation |
|
Digestible Energy (kcal/kg) |
NRC (1977) |
2500 |
2100 |
2500 |
2500 |
|
F. Lebas (1980) |
2500 |
2200 |
2500 |
2700 |
|
|
Crude Fiber (%) |
NRC (1977) |
10-12 |
14 |
10-12 |
10-12 |
|
F. Lebas (1980) |
14 |
15-16 |
14 |
12 |
|
|
Crude Fat (%) |
NRC (1977) |
2 |
2 |
2 |
2 |
|
F. Lebas (1980) |
3 |
3 |
3 |
5 |
|
|
Crude Protein (%) |
NRC (1977) |
16 |
12 |
15 |
17 |
|
F. Lebas (1980) |
15 |
13 |
18 |
18 |
|
|
Calcium (%) |
NRC (1977) |
0.4 |
-- |
0.45 |
0.75 |
|
F. Lebas (1980) |
0.5 |
0.6 |
0.8 |
1.1 |
|
|
Phosphorus (%) |
NRC (1977) |
.22 |
-- |
0.37 |
0.5 |
|
F. Lebas (1980) |
.3 |
0.4 |
0.5 |
0.8 |
You can see that "maintenance" rabbits have the lowest nutritional requirements. Maintenance rabbits are rabbits that are fully grown and are not pregnant or raising litters, so pet rabbits would fall under this category as well as adult bucks and does with longer gaps between litters. Growing kits and pregnant does have similar requirements of more digestible energy and higher protein especially. Does that are nursing kits have notably higher requirements as well and it is very important to make sure they are meeting these requirements for adequate milk production and to allow the doe to maintain her body condition.
What happens when these requirement are not met?
While this is by no means an exhaustive list, some symptoms of nutrient deficiency or excess are listed below.
|
Nutrient |
Deficiency |
Excess |
|
Digestible Energy |
Weight loss, poor growth, reduced milk production, ketosis, ketoacidosis, fatty liver |
Enteritis, obesity, reduced reproduction |
|
Fiber |
GI stasis, wool block, enteritis |
Reduction in digestible proteins creating an energy deficit |
|
Fat |
Dull coat, reduced energy intake, reduced milk yield, reduced vitamin absorption |
Reduced growth and reproduction, enteritis, heart disease |
|
Protein |
Muscle loss, stunted growth, fatty liver, reproductive disorders |
Excess excreted through urine, kidney damage |
|
Calcium |
Hypocalcemia, osteoporosis, rickets, impaired zinc and phosphorus absorption |
Excess is excreted through the urine which may cause bladder or kidney stones |
|
Phosphorus |
Rickets, osteomalacia, infertility, abnormal behavior |
|
|
Magnesium |
Wool block, poor growth, alopecia, convulsions |
Excess is excreted through the urine |
|
Copper |
Anemia, reduced growth, bone abnormalities, greying of black hair, wool block, enteritis |
Copper poisoning |
|
Vitamin A |
Infertility, abortion, weak newborn kits, ocular lesions, hydrocephalus |
Infertility, abortion, weak newborn kits, hydrocephalus |
|
Vitamin K |
Muscle weakness, paralysis, respiratory distress, abortion, placental hemorrhage |
Nephritis |
|
Vitamin D |
Dental problems, weakened immune systems, cardiovascular problems |
Impaired movement, anorexia, infertility |
|
Vitamin E |
Reproductive failure, myopathy |
|
Nutritional Content of Hay
Let's look at how hay compares to the nutritional requirements of rabbits above. Timothy hay, which is very commonly specifically recommended for rabbits, averages only 8% protein which is below requirements for all stages of life and production including a maintenance rabbit. It also averages 1800kcal/kg of digestible energy which is also below requirements for maintenance. Alfalfa hay, on the other hand, tends to be 12.9-18% protein depending on maturity which can perfectly meet protein requirements depending on quality of the hay, although the calcium content of alfalfa can be too high at 1.2% on average, causing it to be avoided or limited by many.
Quality of hay makes a huge difference in how nutritious it is. If you feed packaged hay from the store or buy tested hay, you can check the feed label for nutritional content. If you feed untested hay, you can try to estimate what it may contain based on the grass/legume content, the quality of the hay, and compare to averages for hay of that type and quality. When the plant matures past its peak quality, the cell walls become more lignified and increasingly less digestible, especially including a pretty significant drop in protein content after plants move from a vegetative state to seed head production. You want to look for young, tender leaves, stems that aren't super thick, and less maturity of seed heads in the hay. You will also want to look for a lot of leaves compared to stems as those are the most nutritious component. First cutting hay is generally lower quality because the plants grow super quickly in the spring and the weather conditions are often too cool/moist to harvest on time in late spring or early summer, delaying harvest to when the crop is losing nutritive value. That isn't to say that you can't have a high quality first cutting or a low quality second cutting though, so talk to the farmer, pay attention to how mature the hay looks, and try to get tested hay if possible. Also, if you have had a particularly wet year, chances are the hay will be lower quality, as farmers have to wait for dry windows of time to harvest with plants growing very quickly in the mean time.
Feeding of Pellets with Hay
Pellets are often what is compared to hay or fed in addition to hay, so important to discuss in this context. A good quality pellet is composed of mostly "hay" itself (alfalfa, grass, or both) and also is balanced to meet a rabbit's daily requirements including vitamins and minerals. These pellets are known as "complete" pellets and as the name implies, they are designed to be fed as the complete diet. It is important to follow the feeding directions on the bag for these pellets, as nutritionists have done the hard work of making sure they contain everything needed for your rabbit to have a balanced diet as long as the pellets are fed as directed. Most complete pellets will list how much pellet to feed daily according to your rabbit's body weight. Some hay can be fed on top of that, but if you feed less pellet than the daily recommended serving and replace it with hay, the rabbit is likely not meeting requirements.
Balancing Diets
Many people feed their rabbits some proportion of both hay and pellets, while some feed veggies and greens, specifically exclude pellets, or feed only pellets, but how do you make sure that your rabbit's diet is meeting its nutritional requirements? With any feed, the quality of the feed matters. There are good quality pellets and cheap ones full of fillers, good quality hay and overly mature hay that is so low in nutrition it is like feeding straw, and veggies and greens that offer good nutrients while others offer little at all. It is important as rabbit raisers that we evaluate the nutritional content of what we are feeding our rabbits and the individual quality of the feed. If you feed a complete pellet, but only provide a portion of the recommended serving and fill up the rest with Timothy hay, the rabbit will not be getting enough protein and will likely also not be meeting other requirements such as digestible energy and vitamins. Continuing to use an average 8% protein Timothy hay as the example, the more hay you feed, the richer the rest of the diet needs to be to make up for it. Half a daily serving of a complete diet and the rest Timothy hay will not provide enough protein, but supplementing with a "concentrate" like grain could help make up for the difference. Nutrients like vitamins are a lot harder to balance this way and shouldn't be overlooked.
If wild rabbits eat grass, how can feeding natural grass diet not be providing enough nutrition?
Wild animals instinctually seek out the nutrients that they need. Besides eating grass and other greens, they also seek out bark, twigs, buds, fruits, seeds, and more. Every year I see young cottontails licking the gravel in our driveway. Could they be seeking out salt left behind from the previous winter roads or maybe minerals, I don't know, but the rabbits know that they need something that is there. This kind of foraging based on the rabbit's own instinct is simply not possible with feeding of domestic rabbits. Domestic rabbits only have access to the the feed that you provide them in the quantity that you provide as a daily ration. Where a wild rabbit will select only the tastiest and most nutritious bits of feed and leave the rest, the domestic rabbit only has the quantity provided to eat. This is why it is so important to make sure that the feed you are providing your rabbit with, whatever feed that may be, is meeting their nutritional demands.
Why feed hay?
During digestion, larger (indigestible) fiber particles are moved through the colon where they are later excreted as hard fecal pellets while smaller (digestible) fiber particles (<0.3mm) are moved through the cecum where they are fermented and excreted as cecotrophs (night droppings) which the rabbit then consumes again. These larger particles mechanically stimulate motility of the cecum and colon. Very fine particle size feeds lead to increased retention time in the gut, lowering GI motility. The question then becomes: how fine is too fine? Obviously particle size of long stem hay is greater than that of a pelleted feed, but is the particle size of a coarsely ground pellet large enough? There have been several research studies (some referenced below) on the effect of pellet particle size with somewhat inconclusive results on GI health, but fairly consistent results of increased growth and nutrient utilization by rabbits fed a finer particle feed. While I don't have an answer to if average pellets contain large enough particle size for optimal GI health, I do know that quite a few rabbit raisers feed pellets exclusively with no issues. For someone feeding exclusively pellets, I would personally suggest that they try to find a coarsely-ground pellet or feed just a little bit of long stem hay in addition to the full daily ration of complete pellet. Pellets manufactured by an extrusion process may also tend to retain longer particle length.
A common misconception is that hay is required to wear down a rabbit's teeth. Rabbits have constantly growing teeth, but proper dentition or "bite" is largely genetic and will prevent teeth from overgrowing. If a rabbit has a bad "bite" the teeth will not get worn down properly even on a diet heavy in hay. Many rabbit raisers who feed no hay (exclusively pellets) never encounter malocclusion because they breed for proper dentition in their animals. Müller et al. (2014) studied diet form effect on dental growth and wear and concluded that diet alone is not likely to cause dental problems due to flexible growth that reacts to wear and found no difference between animals fed hay or pellets.
Hay has value as behavioral enrichment for rabbits, helping to relieve boredom and encourage natural behavior. While there are many things that can be provided as behavioral enrichment, rabbits do love to chew on and make a mess of hay. This is an additional benefit of feeding hay outside of nutrition.
Conclusion
While there are many different types of food that can be fed to rabbits, the most important consideration is that the total ration meets the nutritional demands of the rabbit. Timothy hay which is
most commonly recommended for rabbits, in addition to other grass hays,
do not contain enough nutrients on their own to meet nutritional
demands. Common recommendations of large quantities of hay in the diet without proper instruction on balancing the remaining nutrients can be very harmful to the health of these animals. It is very important to balance the nutrients in the entire ration and not just one component of it.
As always, please feel free to contact me or leave a comment below with any questions or comments!
-Barbara
References
NRC Requirements for Rabbits: https://www.nap.edu/catalog/35/nutrient-requirements-of-rabbits-second-revised-edition-1977.
Nutritional pathology in rabbits: http://www.caza-narg.ca/ref/ref200806-7.pdf
Digestive disorders: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7149370/
Evaluation of nutritional content of hay: https://extension.usu.edu/rangelands/ou-files/Deter_forage_value_hay.pdf
General Nutrition of Rabbits: https://www.merckvetmanual.com/exotic-and-laboratory-animals/rabbits/nutrition-of-rabbits#v5625687
Nutrient requirements: https://pdfs.semanticscholar.org/0985/0f88ae2a5af2ccd02d41456991b6128dfac0.pdf
Particle size of feed: Vincenzo Tufarelli , Salvatore Desantis , Sara Zizza & Vito Laudadio(2010) Performance, gut morphology and carcass characteristics of fattening rabbits asaffected by particle size of pelleted diets, Archives of Animal Nutrition, 64:5, 373-382, DOI:10.1080/1745039X.2010.496945
Sogunle et al. 2014 - Feed forms of different particle sizes: growth response, carcass yield and intestinal villus morphology of growing rabbits -
Bulletin UASVM Agriculture 71(1) / 2014Print ISSN 1843-5246; Electronic ISSN 1843-5386
Bulletin UASVM Agriculture 71(1) / 2014Print ISSN 1843-5246; Electronic ISSN 1843-5386
Effect of diet on wear of teeth:
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