CURRENT UNDERSTANDING OF THE ROLE OF THE RETICULUM AND RETICULOOMASALORIFICE IN THE CENTRAL OF DIGESTA PASSAGE FROM THE RUMINORETICULUM OFSHEEP AND CATTLE

Simultaneous abolition of the motility of the ruminoreticulum (RR) and digesta passage from the RR by bilateral vagotomy indicate that the m otility of the RR coordinated with quiescence of the reticulo-omasal o rifice (ROO) are prerequisite for caudal movement of digesta from the RR and forestomach. Rate of passage is of importance in ruminant anima ls since it is related to maximal voluntary feed intake, extent of dig estion of the diet, amount of protein which bypasses the rumen, effici ency of microbial growth, extent of methane loss, and susceptibility o f animals to bloat. In a series of studies, we clarified the roles of frequency, pressure and duration of reticular contractions and the fun ction of the ROO in controlling digesta flow from the rumen in respons e to changes in diets, environmental conditions and physiological stat us. Variability in amount of NDF and OM transferred per contraction su ggests that frequency of reticular contraction is not the rate-limitin g step in digesta passage from the rumen. This concept is supported by our finding that the relaxation of the ROO is not always coincidental with reticular electromyographic activity in solid meal-fed relative to milk fed sheep. The magnitude of reticular pressure may not precise ly control digesta passage through the ROO as the amount of OM and NDF associated with each centimetre of pressure during contraction varies from 1.2 to 1.4 and from 0.9 to 2.5 g. On the other hand, the amount of OM and NDF passed per second of reticulum contraction varies only f rom 0.3 to 0.6 and from 0.2 to 0.3 g, respectively, in cattle. In addi tion, a 38% decrease in mean retention time of particulate matter in t he rumen was associated with a 14% increase in duration of reticular c ontraction in cattle. Similarly, quiescence of the ROO increased from 2.9 to 3.3 s in sheep when feed intake increased from maintenance to t wice maintenance. We suggest that duration of reticular contractions m ay be more closely related to digesta flow than is either frequency or pressure changes. We also suggest that the ruminant animal can influe nce reticular contraction characteristics and duration of the quiescen ce of the ROO in response to various stimuli and that reticular contra ctions are coordinated with other diet and physiological demands for o ptimal transfer efficiency of digesta from the RR.