| Kind of grain. | Ash. | Phosphoric acid in ash. | Phosphoric acid in the entire feed. |
|---|---|---|---|
| Per cent. | Per cent. | Per cent. | |
| Wheat bran | 7.3 | 50 | 3.65 |
| Wheat, grain | 3 | 46.38 | 1.3914 |
| Oats, grain | 2.50 | 26.5 | .6625 |
| Barley, grain | 3.10 | 39.6 | 1.2276 |
| Bean, grain | 3.10 | 31.9 | .9864 |
| Peas, grain | 2.75 | 34.8 | .957 |
| Tare, grain | 3 | 36.2 | 1.086 |
| Indian corn, grain. | 1.5 | — | — |
| Rye, grain | 1.6 | 39.9 | .6384 |
Wheat bran, it will be observed, contains three times as much phosphoric acid as is found in any of the other grains, and four times as much as oats, beans, peas, or rye; so that if fed in excess it will readily overcharge the urine with phosphates.
There is another point to be considered, however, in estimating this danger. Wheat bran contains a far greater quantity of albuminoids and other nitrogen-containing constituents than the common grains (these being made up mainly of starch, which contains no nitrogen); and, all nitrogen-bearing products contained in the blood and tissues being expelled from the body mainly through the kidneys in the form of urea and (in cattle) hippuric acid, it follows that the excess of urea formed when such feed is consumed must load the urine with solids and bring it constantly nearer to the point of saturation, when such solids (or the least soluble of them) must be deposited.
The following table will show the relative amounts of the nitrogen-bearing products in wheat bran and some of our common grains:
| Kind of grain. | Albuminoids (nitrogenous). | Woody fiber (nitrogenous). | Total nitrogenous- bearing constituents. |
|---|---|---|---|
| Per cent. | Per cent. | Per cent. | |
| Wheat bran | 16.1 | 8 | 24.1 |
| Wheat, grain | 12.5 | 1.8 | 14.3 |
| Barley, grain | 12.4 | 2.7 | 15.1 |
| Oats, grain | 11.8 | 9.5 | 21.3 |
| Rye, grain | 10.6 | 1.7 | 12.3 |
| Indian corn | 10.1 | 1.7 | 11.8 |
It will be observed that, with the exception of oats, none of the grains contain more than two-thirds of the nitrogenous material present in the wheat bran, while in the case of rye and maize there is practically but one-half. Even in the case of oats the albuminoids, which are the more digestible principles, and therefore those that are the most easily and speedily converted into urea, are present only to the amount of two-thirds of that which exists in the wheat bran. With such an excess of ash, of phosphates, and of nitrogenous (urea-forming) constituents in wheat bran, its tendency to favor the formation of calculi is fully explained. It must not, however, be inferred that wheat bran is not a valuable feedstuff. The inference is only that it should be fed with an abundance of water, as a sloppy mash, or in combination with an abundance of roots, potatoes, pumpkins, or other succulent aliment.
In this connection the presence of magnesia in the feed or water must be named as favoring calculous formations in the urinary passages. The explanation is that while the phosphate of magnesia thrown out in the urine is soluble in water, the compound phosphate of ammonia and magnesia is insoluble, and, accordingly, if at any time ammonia is introduced into urine containing the phosphate of magnesia there is instantly formed the ammonio-magnesium phosphate, which is as promptly deposited in the solid form. The common source of ammonia in such cases is from decomposition of the urea in fermenting urine. In order to produce this a ferment is necessary, however, and therefore, as an additional prerequisite, the presence of bacteria, or fungi, in the urine is essential. These ferments may make their way from without along the urinary passage (urethra), and their propagation in the bladder is greatly favored by the prolonged retention of urine, as in case of spasm of the neck of the bladder or obstruction by an already existing stone. Another mode of entrance of the ferment is an unclean catheter used to draw the urine. Still another is the elimination through the kidneys of the bacteria of infectious diseases, or of such as, without producing a general infection, yet determine fermentation in the urine. The precipitation is favored not only by the production of ammonia, but also by the formation of viscid (colloid) products of fermentation. In this sense bacteria are most important factors in causing gritty deposits in the urine.
Another insoluble salt which enters largely into the composition of many urinary calculi of the ox is carbonate of lime. This is derived mainly from the lime in the feed and water and from the carbon dioxid formed by the oxidation of the organic acids in the fodder. These organic acids, being composed of carbon, hydrogen, and oxygen (without nitrogen), are resolved by the addition of oxygen into carbon dioxid (CO2) and water (H2O). The carbon dioxid unites with the lime in the blood to form carbonate of lime, and in this state passes into the urine. Now, carbonate of lime is soluble in water containing free or uncombined carbon dioxid, but is precipitated whenever the latter is withdrawn. It is only necessary, therefore, to have in the urine sufficient lime or other available base to unite with all the free carbon dioxid in order to bring about the precipitation of the dissolved carbonate of lime in the solid, crystallized form; hence it is that, of all sediments in the urine of herbivora, this is the most frequent and usually the most abundant.
A less common constituent of urinary calculi is the insoluble oxalate of lime. In this case the lime is derived as before from the feed or water, or both, while the oxalic acid is a product of the oxidation of organic acids of the feed, less oxygen having been used than in the formation of carbon dioxid. The final product of the complete oxidation of these acids is carbon dioxid, but when less oxygen is furnished, owing to some disease of the lungs or a disease of the nerve centers, which lessens the activity of the breathing, then oxalic acid may be produced. If this oxalic acid comes into contact with lime, it is instantly precipitated as crystals of oxalate of lime.
Another inorganic substance at times found in urinary calculi is silica (SiO2). This contributes largely to giving stiffness to the stems of growing plants, and in most of our cereals and grasses makes up a large proportion of the ashes of the burned plant. It is found in the soluble form in combination as silicate of potash, but at times is displaced by oxalic or other acid and then appears as gritty, sandy particles in the stem. This gritty, insoluble silica is especially noticeable among the horsetails (Equisetacæceæ), bamboos, and sedges. The per cent of silica in the ash of several common fodder plants is given below: