Milch cows are probably more open to the attacks of the germ because their systems are reduced by simultaneous milking and breeding through a number of years. Exertion or fatigue has a potent influence in developing the symptoms, so that it is a common practice in the vicinity of infected localities to subject animals to a good run before purchasing. Paradoxically enough the infected milch cow which is distributing the infecting element freely in her dairy products usually shows, in herself, no distinct symptoms of the disease. If she is dry or farrow she suffers like any other animal, but if in full milk, the toxins, and even the hypothetical microbe, seem to escape in that secretion, which proves highly poisonous to other animals, while the cow retains her spirits, vigor and outward appearance of health. Steers, bulls and heifers, on the other hand, show violent symptoms.
Calves suffer so long as they suck the milk. The dead calf is eaten by swine, which suffer in their turn, and the dog contracts the disease by eating one of these animals, or by taking infected milk or cheese. The buzzard eats the dead dog and dies as the result.
Incubation is from 8 to 12 days, though it may be reduced to two. (Beach.)
Symptoms. In the domestic animals the first indication of illness is a lazy, tardy disposition, The subject stands apart from the herd, with drooping head and ears, listless, indifferent to all around him, and often without appetite; or, in cattle or sheep, rumination. There is usually extreme thirst, but without correspondingly free urination or defecation. Peristalsis is virtually abolished and nothing whatever passes from the bowels. The patient is likely to be found lying down and it is difficult to get him up, and when raised he moves stiffly and with reluctance.
In milking cows there may be no symptoms until the animal is excited or fatigued by violent or continued exercise, as a hard run, or a drive of four or five miles. This developes the tremors alike in milch cows and in the mild cases in dry cattle or sheep. The subject stands still and trembles in a striking way, the action resembling the muscular contractions seen after the removal of the hide in an animal newly killed. The head and ears are drooped, movements are uncertain and stiff, and the animal may even drop dead on the spot.
As the disease advances the muscular debility becomes so great that the animal lies down if possible, and if once down he seldom rises again. The decubitus is extended, the head being stretched on the ground. There is a most complete apathy, the subject showing no fear, no apprehension, no disposition to escape or resent injury. The wildest or most timid steer can be freely handled, and there is no disposition to flight or retaliation. The eyes are bloodshot and become fixed and glazed, winking ceases, the breathing is slow, pulse infrequent, and temperature often subnormal. The extremities and surface of the body are cool, the muzzle dry, the coat usually stares, the apathy merges into a complete hebetude, torpor and coma, in which condition the animal often dies on the eighth or tenth day. Violent exercise precipitates the death at once. Recoveries are infrequent and attended by no critical discharge from bowels or kidneys, only by a slow, at first almost imperceptible, resumption of natural action.
The milder cases, those that show no appreciable symptom when at rest, are seized with trembling or rigor when made to undergo the slightest exertion; they appear haggard, stupid and spiritless, drag their limbs slowly and stiffly and quickly stop from pure weariness and debility.
The prostration is even more marked in sheep, which often seem unable to rise, or lack the nervous energy to do so.
Calves tremble while sucking, and will sometimes leave the teat, vomit the contents of the stomach, fall down and perish.
In Vomiting Animals (pig, dog,) emesis usually occurs, and torpor of the bowels or obstinate constipation is present. Pigs burrow under the litter and are driven out with difficulty, and dogs when called on to follow, do so reluctantly, slowly and stiffly and fail to keep pace with their master (“the Slows”).