ACUTE EFFECTS OF AN ANIONIC DIET ON BONE-MINERAL HOMEOSTASIS IN THE BOVINE

Fifteen Friesian oxen between 12 and 18 months of age with a mean body mass of 240.7 kg were randomly assigned to diets containing 0.25% pho sphorus (P) or less, to evaluate the acute effects of an acidiogenic d iet of -11.1 meg/100 g of diet dry matter, compared with a basiogenic diet of +25.6 meg/100 g or a control diet of +16.5 meg/100 g of diet d ry matter calculated as (Na + K)-(Cl + S), on blood, bone and faecal P , calcium (Ca) and magnesium (Mg) for a period of 9 weeks. Blood, bone and faecal responses to an anionic diet are described. An inverse rel ationship existed between bone and blood Ca, in which there was resorp tion from bone with increased blood Ca in response to the anionic diet . The anionic treatment group demonstrated simultaneous increases in b one, blood and faecal P concentrations at various stages of the experi ment compared to the cationic and control treatment groups. Results in dicate independent absorption and resorption of Ca and P into and out of bone. There was wide variation in the bone Ca:P ratio between 2.02 and 1.51 among animals fed the anionic diet, with the Ca:P ratio follo wing Ca values and not bone P values. Bone and blood P had a linear re lationship with dietary cation:anion balance (DCAB), increasing as the diet became more anionic in nature, but faecal P was curvilinear with highest concentrations at -11.1 and +25.6 meg/100 g compared to +16.5 meq/100 g. Concurrent blood, bone and faecal P increases at some stag es of the experiment indicate a P-sparing effect of the anionic diet a nd warrants further research into the long-term effects of anions in t he diet, leading to their use as a possible addition to improved licks in P-deficient areas.