Overfeeding is not without its influence, especially when on animal food, which charges the kidneys with excreting an excess of the irritating urea and uric acid, and this is one reason why it is far more frequent in house dogs than in other domestic animals. When the meat is already decomposing and putrid there is the added evil of a quantity of toxins and even of microbes to be eliminated from the system by the much abused kidneys. Add to these that the dog’s urine is even in the normal condition more dense and contains more irritating ingredients than that of herbivora, and that owing to the slight activity of his perspiratory apparatus he can obtain less relief from the skin, and we find a substantial ground for the prevalence of chronic nephritis in this animal.
Disease of the valves of the right heart or dilatation with insufficiency of the auriculo-ventricular valves is a potent cause of nephritis, the reflux of blood into the veins and the increased venous tension, speedily producing passive congestion and a slow type of inflammation in the kidney. This factor is especially liable to operate in dogs, which are particularly obnoxious to rheumatism and valvular ulceration, and are very subject to nervous cardiac disorders; in horses that have contracted heaves; and in beef breeds of cattle which suffer from fatty degeneration of the heart with dilatation.
The influence of calculi must not be overlooked, whether they are lodged in the pelvis, the chalices, or the uriniferous tubules. Their tendency is to induce local irritation and exudation, with fibroid degeneration and thickening of the walls of the tubules or pelvis and of the adjacent tissue.
When to one or more of the above conditions there are added overfeeding or what is worse a low condition from starvation or unwholesome food (permeated by bacteria or cryptogams or containing vegetable acids), and when to crown all there are frequent exposures to cold or wet, we have a vicious combination especially conducive to kidney trouble.
Habitual retention of urine in mares in harness, in house dogs, or in horses in railway cars, and violent exertion, or sprains of the back are among the remaining accessory causes.
Symptoms. These are often slight or obscure, so that not only owners and attendants but even veterinarians are liable to overlook them. Loss of flesh, flabbiness of the muscles and a lack of spirit and energy are among the first symptoms. The horse appears stiff, especially in his loins and hind limbs, and fails to advance the hind feet as far under the belly as formerly, and straddles more. When put to work he is early fatigued and appears unfit for sustained exertion. His movements are slow and if urged to a trot he may even groan with every step and quickly settles back to his sluggish pace. If turned sharply round on himself he does so with difficulty and often groans. When he is mounted or when the loins are pinched he may droop to excess. If you come on him lying down, and urge him to rise he may rise on his fore limbs and sit on his haunches until urged before he makes any attempt to raise himself on his hind. The dog may spend most of his time in the kennel, and show little disposition to run, play or hunt. On the contrary the owner may have to call him several times before he will come out and then he moves listlessly, wearily and even weakly.
In all animals the appetite is poor or capricious, and the patient gradually loses condition, at first slowly and later, after a few weeks or months, more rapidly. The advance of anæmia is also steadily progressive.
Dropsical effusion is not uncommon. It is often prominent in the horse as stocked limbs, but may be absent for a length of time. In other animals it is more likely to appear later in the disease and under the chest or abdomen or in one of the internal serous cavities. Trasbot has found it absent for months in the nephritic dog.
The exploration of the kidney through the flaccid abdominal walls in small animals, and through the rectum in small horses and cattle, may reveal renal tenderness and even swelling. If there is a tendency to frequent passage of urine in small quantities, or to straining without micturition, the indication is of value.
There may be little or no fever, and, when left at rest, little evidence of discomfort.