Investigations with15N'‐labelled urea were carried out to find out the influence of the amount of fibre on the reflux of15N’ into the caecum to take part in the caecal metabolism. Two pelleted diets, containing 9.7% (group 1 with 23% oat hulls) and 2.2% (Group 2 without oat hulls) crude fibre, with urea with 60 atom%15N‐excess (15N) used as marker were given to three White New Zealand rabbits each group. Group 1 and 2 consumed 109 and 72 g fresh matter per rabbit and day, respectively. Daily15N'‐intake per rabbit was 307 mg in group 1 and 279 mg in group 2. Most of15N’ was eliminated directly via the urine. The daily faecal excretion in group 1 and 2 was 5.3 and 2.3 mg15N’, respectively. Only about 20 to 30% of15N’ and volatile fatty acids in the caecum and higher amounts of15N’ in muscles were found. The animals of this group consumed nearly the total amount of faeces by caecotrophy. Therefore 24 g of group 2 was still satisfying compared to 33 g live weight gain/rabbit and day of group 1. It is concluded that the animals of group 2 could compensate the low fibre level within a period of about 20 days by a more efficient utilization, the consumption of crude protein and starch being 18 and 12% lower than in group 1, respectively. Feed intake and health status were not evidently affected. The results are in contradiction to the common knowledge.