Studies on the alimentary tract of the merino sheep in South Africa. XVI. The fate of nitrate in ruminal ingesta as studied in vitro

Abstract

1. In vitro experiments have been conducted on the disappearance of potassium nitrate in ruminal ingesta from sheep on different diets. 2. Nitrate disappears more rapidly from ingesta of lucerne-fed sheep than from that of sheep on grass hay. 3. Nitrite is formed from the nitrate. It appears very soon after the addition of nitrate to the ingesta, reaches its maximum concentration at the moment of complete disappearance of the nitrate and subsequently itself disappears. Nitrite thus formed represents an intermediate stage in the conversion of nitrate to more fully reduced compounds. 4. The ratio nitrite disappearance time / nitrate disappearance time is constant for varying quantities of nitrate (Constant A). 5. The nitrite formed also disappears more rapidly from ingesta of lucerne-fed sheep than from that of sheep on grass hay. 6. The disappearance of nitrate from ingesta is represented graphically by plotting quantity of nitrate against time of disappearance. The resulting curve is a half parabola, with values varying for different ingesta. Daily variation for ingesta can be plotted from a series of such curves. 7. Nitrate disappearance rate can be used as an additional measure of ruminal activity. 8. The addition of glucose shortens the time of nitrate disappearance; the maximum effect for a fixed quantity of nitrate is produced by as little as 15 to 30 mg. of glucose per 20 c.c. of ingesta. 9. The "nitrate disappearance curve" is shifted in position, but remains unaltered in relative proportions, by the addition of a fixed quantity of glucose to the tube in each reading. The percentage reduction of time of disappearance of different quantities of nitrate due to a fixed quantity of glucose is a constant (Constant B). 10. The time of disappearance of nitrite formed from the nitrate is similarly affected by the presence of glucose. The percentage reduction of nitrite disappearance time due to a fixed quantity of glucose is also constant (Constant C). 11. "Nitrite persistence" is defined as the interval of time between the disappearance of nitrate and of nitrite. The percentage reduction of nitrite persistence due to a fixed quantity of glucose constitutes a fourth constant (Constant D). 12. An in vivo experiment confirmed the in vitro findings on the effects of nitrate, supplied either alone or in conjunction with sugar, on the ruminal ingesta of sheep. It demonstrated clearly the effect of diet and of sugar on nitrate persistence and therefore on nitrite poisoning. 13. Further work on this subject, both from the toxicological and the nutritional aspects, is in progress.