Influence of passage model and caecal cannulation on estimated passage kinetics of roughage and concentrate in the gastrointestinal tract of horses

The objectives of this study were to evaluate the use of non-linear passage models to estimate total tract retention time and hindgut fractional passage rates of hay and concentrate, and to investigate the effect of caecal cannulation on passage parameters in horses. Animals were four geldings of Norwegian Cold-blooded Trotter fed a hay and concentrate diet at a dry matter intake of 1.7% of body weight. Marker studies were conducted one month before and three and 15 months after caecal cannulation using Cr-mordanted hay and Yb-labelled concentrate as markers. Faecal marker excretion curves were fitted either to one-compartment models with gamma time dependency (Gn) or to two-compartment models (GnG1), with gamma time dependency in the first compartment (Gn) and time independency in the second one (G1). Lowest error mean square was observed for the G4 and G4G1 models. Caecal cannulation increased total tract mean retention time (TMRT). No differences were observed between hay and concentrate in TMRT or fractional passage rates. It is concluded that using time dependent passage models will improve our understanding of passage kinetics in horses and that there is only minor differences between hay and concentrate in hindgut retention time.