2.2. Digestibility trial
The coefficients of total tract apparent digestibility (CTTAD) of dry matter and nutrients and the digestible energy (DE) concentration of each experimental diet were measured in an in vivo digestibility assay carried out on 60 rabbits among those being tested (10 animals of both sexes per diet) according to the European standardized method ( Perez et al., 1995). The digestibility trial started at 52 d of age with a 4-d collection period.
2.3. Sampling of caecal content and intestinal mucosa
A total of 36 rabbits (6 rabbits per experimental diet) out of the 246 initial rabbits were slaughtered at 51 d of age to sample caecal content and intestinal mucosa. The slaughtered animals were representative of the corresponding experimental group in terms of average live weight and variability. The rabbits were slaughtered between 08:00 and 12:00 h. They were weighed immediately before slaughtering by cervical dislocation. Thereafter, the full gut and then the stomach and the caecum were separated and weighed. The caecum was removed and the pH of the caecal content was immediately measured. The caecal content was diluted with a 15% HPO3 solution (25%, w/w), and stored at −20 °C pending chemical analysis.