If given the choice, should rabbits eat fresh grass or hay?

Fresh Grass vs. Hay: Which One Should Rabbits Eat?
By Asst. Prof. Dr. Somphoch Weerakul (Ajarn Kaew)

This question has been answered many times—probably for over 20 years—and will likely continue to be answered as long as people are interested in keeping rabbits and as new rabbit owners emerge. When people read recommendations from experts or veterinarians, particularly those from different countries, they may feel either skeptical or inclined to agree. Many wonder why there are differing recommendations.

In reality, veterinary health sciences should follow the same fundamental principles worldwide. However, knowledge is not always disseminated equally, and the strictness of care and health management varies. Most importantly, scientific recommendations should be backed by research and continuous updates to ensure that information remains current.

To understand the reasoning behind choosing between fresh grass and hay, one must delve into the composition of the grass itself. The selection of grass, regardless of its type, should consider its fiber content and protein levels, which vary based on species, maturity stage, harvesting method, cultivation quality, climate, water, and soil conditions. These factors significantly influence the nutritional value of the grass.

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1. The Role of Dietary Fiber

The first and foremost criterion when selecting grass for rabbits is its fiber content. There are two main types of fiber found in grasses:
• Digestible fiber: Includes pectin and hemicellulose, which are utilized by the rabbit’s gut bacteria for fermentation, serving as a primary energy source.
• Indigestible fiber: Includes lignin and cellulose, which play a crucial role in stimulating gut motility and maintaining a healthy digestive system.

The proportion of these fibers must be balanced. Young plants, vegetables, and fruits contain more digestible fiber but less indigestible fiber. Rabbits that consume primarily these foods may suffer from gastrointestinal (GI) stasis, microbial imbalance, and premature death.

15-20 years ago, rabbits in Thailand had significantly shorter lifespans, averaging only 4-6 years. However, with improved dietary awareness, the lifespan of pet rabbits has increased, with many now living beyond 10-14 years.

On the other hand, overly mature plants develop thicker cell walls, leading to lower digestible fiber and higher indigestible fiber, similar to tree bark. Rabbits consuming overly mature hay may experience weight loss and stunted growth from inadequate nutrients, despite large and well-formed feces due to high fiber stimulating gut motility. However, this is not an ideal stage for rabbit consumption.

Additionally, young plants, vegetables, and fruits contain high levels of pectin, sugar, and starch (carbohydrates), which can be rapidly fermented by lactic acid bacteria, leading to excessive lactic acid production. This can cause acidosis, abdominal pain, gut inflammation, and histamine release throughout the body. Affected rabbits may exhibit lethargy, appetite loss, abnormal feces, mucus stools, or cecotrope avoidance. In severe cases, this can escalate to GI stasis and enteritis, leading to fatal outcomes.

Conversely, overly mature grasses and straws (such as late-harvested Pangola grass or rice straw) have excessive lignin and cellulose, promoting bowel movements but offering low nutritional value. This can result in malnutrition, stunted growth, pregnancy issues, and weak offspring. Furthermore, these grasses alter gut pH, making it more alkaline, which favors harmful bacteria over beneficial gut flora, increasing the risk of gut infections.

However, tree bark from mature plants can help naturally wear down rabbit teeth, as it contains silica, keratin, and cutin.

Ultimately, determining the “best” grass is not straightforward—it requires scientific analysis and long-term observation rather than relying solely on marketing claims.

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2. Protein Levels in Grass

Protein content is another crucial factor in assessing grass quality. Different grasses contain varying protein levels, influenced by harvest timing.

In the U.S. and Europe, hay is classified into Super Premium, Premium, or Standard grades, based on nutritional value and harvest frequency (e.g., first-cut, second-cut, or third-cut hay). High-quality hay undergoes nutritional analysis to determine protein levels, which serve as a key indicator of its grade.

For example:
• Timothy hay: Typically contains 8-12% protein (or higher in some cases).
• Oat hay: Contains around 10% protein.
• Alfalfa hay (a legume, not grass): Contains 15-21% protein.
• Poorly cultivated or aged grass: Can have protein levels as low as 1-3%, making it nutritionally inadequate.

High-protein plants promote growth, which is why alfalfa is commonly recommended for young rabbits to support bone development due to its high calcium content. As rabbits mature, they require Timothy hay, which provides moderate protein and high digestible fiber, maintaining optimal gut function and overall health.

Studies have shown that Timothy hay’s digestible fiber is particularly beneficial, with average indigestible fiber at 66.6%, aligning with the ideal fiber ratio for rabbits. (Trocino et al., 2012).

Other grass types can be fed as alternatives, provided their nutritional content is appropriate and the rabbit maintains good health. However, fiber balance should always be a key consideration.

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Fresh Grass vs. Hay: Which is Better?

Both fresh grass and hay have their benefits, and if their nutritional values are comparable, fresh grass may offer additional advantages, including:
✅ Higher palatability (more appealing taste and aroma)
✅ Better retention of vitamins
✅ Supports natural foraging behavior

However, fresh grass also comes with challenges:
❌ Shorter shelf life (prone to spoilage)
❌ Higher moisture content, increasing the risk of mold contamination
❌ Inconsistent quality if sourced from unregulated farms

Rabbits consuming a poorly controlled diet tend to have higher rates of illness. Studies show that rabbits fed vegetables, fruits, and treats have 5.29 times higher chances of health issues (p<0.05) than those fed a well-balanced diet, even when provided with unlimited hay.

Additionally, rabbits consuming less than 75% hay in their diet have a 92% higher risk of GI stasis.

Thus, veterinarians often recommend strict dietary management to prevent health complications and extend rabbit lifespan.

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Conclusion: Which Should You Choose?

Whether you choose fresh grass or hay, close monitoring of your rabbit’s health is essential. A well-maintained rabbit should exhibit:
✅ Consistent, well-formed feces (0.5-1.0 cm in size)
✅ No abnormal mucus or loose stools
✅ No signs of bloating or gas accumulation
✅ No history of GI stasis or dental disease

Veterinary check-ups, including X-rays for gas accumulation, can further confirm dietary suitability.

Most owners prefer hay due to its controlled quality, ease of storage, and lower contamination risk. However, providing carefully selected fresh grass as an occasional supplement can enhance a rabbit’s quality of life, provided it is not too young (high in starch) or too mature (low in nutrition).

Ultimately, the best choice depends on availability, quality control, and the rabbit’s individual health status.