Pattern of some internal and external markers along the gastrointestinal tract of cattle

The pattern of distribution of some internal and external markers along the gastrointestinal tract of cattle was measured and used to estimate diet digestibility and transit time. On the day before slaughter, part of the cows' hay diet was replaced with chromium and ytterbium mordanted hay. The cows were subsequently slaughtered and their digestive tracts dissected and the contents analysed. Chromium concentrations along the gastrointestinal tract had a lower variability than ytterbium, as had the cutins in comparison with the lignin. The external markers always had lower concentrations than in the feed whilst the internal markers generally had higher concentrations. There was a general decrease of external and internal marker concentrations up to the small intestine; thereafter, internal markers increased and approximated the values observed in the rumen while the concentrations of the external markers remained lower than in the rumen. The estimated rumen rate of passage did not differ between lignin and cutins, with an average value of 0.011 h-1, but these were both significantly lower (P < 0.01) than those estimated with external markers (0.022 h-1 and 0.024 h-1 for chromium and ytterbium, respectively). Calculated rumen digestibility showed significant variations between external and internal markers for crude protein and neutral detergent fibre (NDF), but not for dry matter (DM) and organic matter (OM) degradability; generally, data based on chromium or ytterbium gave higher degradation values in comparison with the internal markers. The rate of digestion (k(d)) digestibility values calculated at the abomasum were more variable and lower than values measured in the rumen. Total tract digestibility (measured at the second section of the colon) varied widely between markers for DM, OM, crude protein and NDF