Rate of passage of digesta in sheep

1.Five sheep were given 400, 625, 850, 1075 and 1300 g lucerne chaff/d according to a 5 × 5 Latin square design to perturbate a mathematical model describing the rate of passage of digesta in terms of rate constants for the reticulo-rumen (k1) and caecum and proximal 2.colon (k2), and a transit time (TT) for the intestines. These values were obtained from the concentration curves of51Cr EDTA and144Ce-144Pr (144Pr) excretion in faeces for comparison with similar measurements obtained directly. 3.The retention times of markers in the reticulo-rumen, caecum and proximal colon and intestines all decreased by approximately 50% as intakes were increased from 400 to 1300 g/d. For both markers, the direct and indirect measures of half-time in the reticulo-rumen were essentially identical. The predicted (indirect) values for half times in the caecum and proximal colon were smaller than the direct values (P < 0.005) but the correlations between them were significant (P < 0.01) for51Cr EDTA (r 0.66) and144Pr (r 0.78). The direct measures of transit time were smaller (P < 0.025) by 5–10% than the predicted values but correlations between them were significant (P < 0.01) for51Cr EDTA (r 0.91) and for144Pr (r 0.93). Thus the model predicted the changes produced in the rate of passage of digesta and its usefulness and limitations are discussed. 3.With144Pr 1/2k1 for the reticulo-rumen and T1/2k2 for the caecum and proximal colon were both positively correlated (P < 0.025) with the organic matter digestibilities. T1/2k2 decreased at half the rate of T1/2k1 with increasing intakes. This would have favoured compensatory digestion in the large intestine.