16d • Rabbit Nutrition
Rabbits and Long Fiber .
A lot of the confusion around rabbit diets comes from how the term “long fiber” gets passed around without context.
In the actual nutrition research, “long” or “structural” fiber is not defined by hay strands.
It’s defined by measured particle size — in millimeters.
In the post-weaning rabbit fiber study (Pakistan Journal of Nutrition, 2019), fiber was classified by particle length, not by whether it came from hay or pellets. The optimal outcomes occurred when rabbits received:
• Adequate NDF fiber
• Medium particle size: 0.5–1.5 mm
That combination produced: – 0% mortality
– Lower E. coli counts
– Lower immune stress markers
– Better overall gut stability
When fiber particles were larger and more heterogeneous, outcomes got worse — even when total fiber was high. Larger particles increased immune activation, stress, and disease susceptibility.
This matters because what is often promoted as “long fiber” in pet advice is actually coarse, loose, lignified hay, which is not how fiber is defined in the studies being cited.
It is not false to say rabbits need medium to longer NDF fiber.
What is misleading is implying that rabbits can only get that fiber from long-stem, loose hay, particularly timothy hay.
In the research, the “longer” fiber fraction is still measured in millimeters, not inches.
That fiber is routinely delivered inside pellets, where particle size, digestibility, and nutrient ratios are controlled.
Timothy hay, by contrast, is:
– Very low in protein
– Extremely high in mostly non-fermentable fiber
– High in lignin and cellulose
– Nutrient-diluting when added to an already balanced diet
The problem isn’t veterinarians or owners acting in bad faith. It’s that much of the advice circulating today comes from advocacy materials and summaries, not from direct engagement with the primary nutrition literature. As that information gets repeated, “long fiber” quietly turns into “hay,” even though the studies themselves never make that leap.
Rabbits need structural fiber, not hay by default.
And in the research, that fiber is defined by particle size (0.5–1.5 mm) and balance, not by loose strands of timothy.
Loose hay is great when fed selectively and carefully as an enrichment item but it does carry more risks .
Feeding pellets that already meet species-level fiber requirements is not “ignoring fiber.”
It’s following the data — precisely.
If you want deeper dives into nutrition check out the nutrition course .
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Rabbits and Long Fiber .
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