Effects of dietary mineral acids on voluntary food intake, digestion, mineral metabolism and acid-base balance of sheep.

I . A pelleted grass meal diet alone (control) or supplemented with hydrochloric acid, sulphuric acid or a I : I mixture of these acids, at 320 mequiv./kg, was offered ad Zib. to eight sheep in a double 4 x 4 Latin square design for 20 d. 2. The HCI and HCl-H,SO, treatments each reduced food intake of the sheep by 19 "/o and the H,SO, treatment reduced it by 3076,. Avcrage daily intake of acid was 397, 333 and 299 mequiv. on the HCI, HCl-H,SO, and H,SO, treatments respectively. 3. Rumen fluid pH was decreased by each acid treatment by 0'1-0'2 units without any appreciable changes in total or individual volatile fatty-acid concentrations. Dry-matter digestibility was slightly increased by each acid treatment. 4. Blood pH, plasma bicarbonate and blood base excess were decreased by each acid treatment; sulphateconcentration in serumwas increased bythe HC1-H,SO,and H,SO, treatments. 5 . In urine the acid treatments decreased the pH from a control value of 8.0 to approximately 6.0; associated with this was a large decrease in urinary bicarbonate and a large increase in urinary ammonia-nitrogen and calcium excretions. 6. The chloride and sulphur contributed by the acid treatments were almost entirely absorbed and excreted in the urine. Each acid treatment caused a negative balance of Ca equal to the increase in urinary Ca. Effects on other minerals were small. 7. The effect of the HCl and the HCl-H,SO, treatments on voluntary food intake is ascribed to metabolic acidosis and of the H,SO, treatment to excess dietary sulphate-S.