Effect of intraruminal osmolality changes arising from administration of sodium chloride on transfer of blood urea to rumen in sheep (Kesan perubahan osmolaliti intraruminal lanjutan daripada pemberian natrium klorida terhadap pemindahan urea darah ke dalam rumen biri-biri)

A single injection of 15 g NaCl into the rumen, which increased the osmotic pressure of rumen fluid from 369 to 474 mOsmol/kg, resulted in a decrease in the transfer of blood urea into rumen fluid from 2.3 to 1.6 g N/day in sheep fed 50 g of chaffed oaten hay every hour. It is concluded that the reduced urea transfer was the result of a reduced urea input via saliva. The rumen wall remained virtually impermeable to urea throughout the study. *Livestock Research Division, Headquarters Station, MARDI Serdang, P.O. Box 12310, 50774 Kuala Lumpur, Malaysia **Department of Biochemistry, Microbiology and Nutrition, University of New England, Armidale NSW, 2351, Australia Authors’ full names: Yusof Hamali Ahmad, John V. Nolan and John Kent ©Malaysian Agricultural Research and Development Institute 1995 Introduction The osmolality of rumen contents has not received much attention as a potential factor influencing urea transfers to the rumen (Egan et al. 1986).The osmolality of rumen contents is quite variable, being influenced by factors such as the type of feed and time of feeding (Warner and Stacy 1965). Net water flux out of the rumen changes with rumen osmolality (Warner and Stacy 1972) and saliva production decreases with increased rumen osmotic pressure (Warner and Stacy 1977) and presence of salts in the drinking water. After a ruminant has eaten, the release of salts and catabolism of polymers increase the rumen concentration of osmotically active compounds and the rumen contents become hypertonic. Under these conditions, water tends to diffuse into the rumen and urea which is also diffusible, may enter together with the inflow water. The permeability coefficients for passive diffusion of urea and water across lipid bilayer membranes, i.e. 5 x 10-2 and 7 x 10-4 cm/s, respectively, are highly relative to many other compounds. It is thus possible