Effects of chronic hydrochloric and lactic acid administrations on food intake, blood acid-base balance and bone composition of the rat.

In experiment 1, weanling rats were given, for 7 weeks, a commercial rat diet supplemented with hydrochloric acid at levels up to 560 mmol.kg-1 dry matter. The supplement increased water intake but did not significantly affect food intake, live-weight gain, blood haemoglobin and haematocrit values or acid-base balance. In experiment 2, adult rats were given, for 9 weeks, a commercial rat diet supplemented with hydrochloric acid at levels up to 1250 mmol.kg-1 dry matter. Food intake and liveweight gain were not affected by hydrochloric acid concentration up to 625 mmole but at 938 mmol.kg-1 they were considerably reduced and there was 100% mortality of the rats. In experiment 3, weanling rats were given, for 12 weeks, a commercial rat diet supplemented with hydrochloric or lactic acid each at 300, 600 and 900 mmol.kg-1 dry matter. Lactic acid at the three levels and hydrochloric acid at the two lower levels did not affect food intake or live weight gain and had only a slight effect on blood acid-base balance. At a dietary concentration of 900 mmol.kg-1 dry matter, hydrochloric acid decreased food intake, induced a mild degree of metabolic acidosis and resulted in 30% mortality of the rats. In the three experiments, the acid treatments dnot directly affect the length or composition of the femur of the rats.

Effects of dietary hydrochloric acid on voluntary food intake and metabolism of sheep in relation to the use of mineral acids as silage additives.

1. In Expt I, a pelleted grass-meal diet was supplemented with hydrochloric acid, added to the grass pellets before feeding, at five levels from 0 to 628 mmol/kg dry matter (DM). Each diet was offered ad lib. for 21 d to five sheep in a 5 x 5 Latin-square design. 2. Voluntary food intake decreased rectilinearly with increasing HCl supplementation (P less than 0.001), to 42% of the control value for sheep on the high-HCl diet. The decrease in food intake was related both to dietary pH and to the extent of metabolic acidosis induced by the HCl treatment. Although the pH of rumen fluid decreased slightly with increasing HCl supplementation, effects of the HCl treatment on volatile fatty acid concentrations in rumen fluid were not significant (P greater than 0.05). 3. In Expt 2, palatability and metabolic effects of dietary HCl were studied by comparing its effect when mixed into the pelleted grass meal before feeding, with and without a supplement of an equivalent amount of sodium bicarbonate given intraruminally, or when HCl was given intraruminally while the sheep consumed pelleted grass meal alone. Each of the three treatments was given at two levels of HCl, 280 and 560 mmol/kg DM. At each level of dietary HCl supplementation, the three treatments and the control diet (pelleted grass meal alone) were each given to four sheep, in a Latin-square design, for 11 d. 4. At the low level of supplementation, HCl, when mixed into the pelleted grass meal, reduced food intake by 17%, this effect was not altered by NaHCO3 supplementation, but when HCl was given intraruminally food intake was not reduced. At the high level of HCl supplementation, food intake was reduced by about 40% by each method of HCl supplementation; and NaHCO3 supplementation did not appreciably alter the effect of HCl on food intake, but prevented metabolic acidosis associated with the HCl treatments. Food intakes for the low-HCl treatments were significantly higher than those for the high-HCl treatments (P less than 0.01) and the level of dietary HCl x treatment interaction was also significant (P less than 0.01). DM digestibility, and the pH and volatile fatty acid concentrations of rumen fluid were not significantly affected by the different treatments. 5. It is concluded that at a low level of HCl supplementation the adverse effects of dietary HCl on voluntary food intake of sheep is determined by palatability associated with low dietary pH, whereas at a high level of HCl supplementation the effect is determined by palatability and by a metabolic response.

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

1. 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 (OM); 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 pH or volatile fatty acid concentrations of rumen fluid. MgO supplementation was only slightly effective in preventing the metabolic acidosis caused by HCl supplementation, as indicated by blood and urine acid-base measurements. 4. With the MgO-supplemented diets, values for the faecal and urinary excretion of magnesium were approximately 70 and 10% respectively of Mg intake and were not significantly affected by HCl supplementation. For rumen fluid, the water-soluble Mg concentration as a percentage of the total Mg concentration was similar for each treatment, approximately 90%. For faeces, the corresponding value was also similar for each treatment, approximately 30%. 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 HCl-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.