Comparison of gut fill in sheep (Ovis aries) measured by intake, digestibility, and digesta retention compared with measurements at harvest
Gut capacity is an important factor in digestive physiology and is often measured as dry matter fill (DMF) following dissection, which prevents repeated measures in the same animal. It was proposed to calculate DMF from food intake, digestibility, and gut mean retention time (MRT), but empirical tests of this are few. We calculated DMF from intake, digestibility, and the MRT of small-particle (1 mm) and large-particle (20 mm) markers in 20 sheep (Ovis aries L., 1758) fed at different intake levels and compared results with DMF at dissection at the end of the feeding trial. MRT for smaller particles was significantly shorter than for larger particles (34.4 ± 6.1 vs. 42.5 ± 7.6 h, respectively). Correspondingly, DMF calculated from smaller particles (0.98 ± 0.27 kg) was significantly lower than DMF calculated from larger particles (1.20 ± 0.30 kg). The latter was not significantly different from DMF measured at dissection (1.18 ± 0.34 kg). These results suggest that DMF can be estimated from measures of digestive physiology. The choice of particle marker to determine MRT is crucial for the accuracy of the proxy. In ruminants, where small particles are consistently eliminated faster than larger particles, considerations of marker particle size are particularly important.