Effect of decreasing dietary @entity3151 supply on net recycling of inorganic XXXX in lactating dairy @entity291 .

@entity2198 @entity58273 @entity3151 @entity1391 @entity4959 @entity3918 @entity291
Five ruminally cannulated lactating Holstein @entity291 , fitted with permanent indwelling catheters in the mesenteric vein, hepatic vein, portal vein, and an artery were used to study intestinal absorption and net recycling of inorganic @entity1391 (P(i)) to the gastrointestinal tract. Treatments were low P (LP; 2.4 g of P/kg of @entity3918 ) and @entity2198 ( @entity2198 ; 3.4 g of P/kg of @entity3918 ). The dietary total P (tP) concentrations were obtained by replacing 0.50% @entity4959 in the LP diet with 0.50% @entity58273 in the @entity2198 diet. Diets were fed for 14 d and @entity291 were sampled on d 14 in each period. @entity291 were fed restrictively, resulting in equal dry matter intakes as well as milk, fat, and protein yields between treatments. Net P(i) recycling (primarily salivary) was estimated as the difference between net portal plasma flux (net absorption of P(i)) and apparently digested tP (feed - fecal tP difference). @entity3151 intake, apparently digested tP, and fecal tP excretion decreased with LP. An effect of decreased tP intake on net portal plasma flux of P(i) could not be detected. However, despite numerically minute net fluxes across the liver, the net splanchnic flux of P(i) was less in LP compared with that in @entity2198 . Though arterial plasma P(i) concentration decreased, net P(i) recycling was not decreased when tP intake was decreased, and recycling of P(i) was maintained at the expense of deposition of P(i) in bones. Data are not consistent with salivary P(i) secretion being the primary regulator of P(i) homeostasis at low tP intakes. On the contrary, maintaining salivary P(i) recycling at low tP intakes indicates that rumen function was prioritized at the expense of bone P reserves.
