EXTENT OF DIGESTION AND RUMEN CONDITION AS FACTORS AFFECTING PASSAGE OF LIQUID AND DIGESTA PARTICLES IN SHEEP

Two experiments were carried out at Mt. Cotton, The University of Quee nsland, from November 1992 to July 1993, to study the effect of extent of digestion or feed type (grass or legume) on particle kinetics in t he rumen. Small (0 . 5-1 . 18 mm) Yb-labelled grass or legume particle s, either digested or undigested, were injected into the rumen of shee p fed on different diets, and their retention time in the reticulo-rum inal compartment measured. In Expt I, four intact wethers were fed on either pangola grass hay, chaffed lucerne hay, pelleted lucerne hay or commercial pelleted concentrate. Digested particles from the faeces o f animals fed on pangola or lucerne and undigested material from the s ame diets were wet-sieved and the fraction 0 . 5-1 . 18 mm collected, labelled with Yb-acetate and injected into the animals together with a solution of Cr-EDTA. Faecal samples were taken and analysed for marke r concentrations. In Expt 2, four similar animals, fitted with duodena l and ruminal cannulae, were fed on different proportions of pangola g rass hay and lucerne hay, and Cr-EDTA and the above mentioned labelled particles were injected through the rumen cannula. Samples were taken from the duodenum and analysed for marker concentrations.The results indicated that diet characteristics rather than extent of digestion or particle type had the greatest influence on rates of passage of both liquid and particulate phases. Different proportions of pangola and lu cerne did not result in marked differences in either the volumes of ru men contents or the rates of passage of the solid phase marker but alt ered the rates of passage of Cr-EDTA. Increasing the proportion of leg ume increased intake and decreased retention time markedly, with no ad ditive effects on digestibility. Particles of the same small size esca ped with the same fractional passage rate within each diet, irrespecti ve of type (grass or legume) or status (undigested or digested), indic ating identical kinetics within each rumen type. It was concluded that rumen conditions as influenced by diet type have most influence on wa ter and particle kinetics and that extent of digestion of the small pa rticles used in our experiments was not important. Particles of legume or grass of the same size behaved similarly within a diet type.