Flow and passage rate studies at the ileal level in the rabbit

Six female rabbits fitted with a simple glass cannula in terminal ileum and a further 6 non-cannulated rabbits were used to perform digesta flow and transit measurements. The animals received ad libitum a diet based mainly on lucerne meal. Flow and transit measurements were carried out using two particulate markers: ytterbium (Yb) fixed on lucerne meal cell-walls by soaking, and chromium (Cr) fixed by mordancing. Both markers were incorporated in the same diet before pelleting. The digestibility coefficient or total mean retention time (MRTt) in the whole tract was not affected by cannulation. MRT values between cecum and rectum could be obtained in cannulated rabbits: 9.6 h. The MRTt values estimated with Yb were higher than those obtained with Cr because the size of particles labelled with Cr was probably greater and thus the particles were excreted more rapidly in hard feces. Flow measurements were not affected by the choice of marker, confirming indirectly the validity of ileal digesta samples. These first ileal flow measures obtained on cannulated rabbits indicate that about half (49%) of the digestible organic matter and two-thirds of the digestible crude protein apparently disappeared before the cecum. Cell-walls (CW), determined as NDF fraction, were totally recovered at the terminal ileum, although hemicellulose (NDF-ADF) digestion could occur in both the small intestine and the cecocolic parts. These results are discussed in relation to the specificity of the Van Soest method for digesta cell-wall analysis.