A study of the effectiveness of calcined magnesite as a neutralizing agent for hydrochloric acid in the diet of sheep

Abstract

I . Five experimental diets were offered ad lib. for 21 d to five sheep in a 5 x 5 Latin-square design experiment as follows: pelleted grass meal alone (control); pelleted grass meal plus hydrochloric acid (470 mmol/kg dry matter (DM)) ; pelleted grass meal plus 470 mmol HCl/kg DM and either an equivalent amount of calcined magnesite (MgO) (235 mmol/kg DM) or twice the amount (470 mmol MgO/kg DM); pelleted grass meal plus 470 mmol MgO/kg DM. 2.MgO supplementation partly prevented the reduction in food intake caused by HCl, being more effective at the low than at the high level. When fed alone, the high level of MgO had a slight adverse effect on food intake.3. There was no significant treatment effect on either the p H or volatile fatty acid concentrations of rumen fluid. MgO supplementation was only slightly effective in preventing the metabolic acidosis caused by HC1 supplementation, as indicated by blood and urine acid-base measurements. 5. MgO supplementation altered the effect of dietary HCl on faecal calcium excretion and on the balance of Ca, but did not alter its effect on urinary Ca excretion.6. It is concluded that the beneficial effect of MgO supplementation on the intake of the HC1-treated diet was related more to its influence on dietary pH than on conditions in the rumen or the acid-base balance of the sheep.