Though not a common disease in the horse yet a large number of cases are
on record, and accidental and experimental cases alike show that this
animal is peculiarly receptive to the disease. The early symptoms depend
on the location of the primary lesions, yet the general phenomena of
debility, languor, early fatigue, unfitness for violent efforts,
perspiration on slight exertion, irregular appetite, occasional rises of
temperature and emaciation may usually be noted. The advance is usually
slow, almost imperceptible, with periods of improvement and aggravation.
Some cases have appeared in the submaxillary and pharyngeal lymph glands
with sore throat and were for a time mistaken for glanders (Ehrhardt,
McFadyean). Others show a swelling of the appearance of cold abscess in
the seat of the prepectoral glands (Johne, Röbert). One showed widely
distributed lymph nodes and enlarged and indurated lymph glands
(prepectoral, inguinal, etc.) with thickening of the intervening lymph
vessels (Cadiot). This last suffered from bronchitis two months before.
A number of cases reported by McFadyean showed special stiffness of the
neck, with swelling and distortion of the vertebral joints, due to a
tubercular osteitis and periostitis, and associated as necropsy showed
with internal tuberculosis. Cases of this kind occurred in the practice
of McConnell, Dawes, Insall, Malcolm and Hill, so that tuberculosis may
well be suspected in cases of disease of the cervical vertebræ. In all
of these cases post mortem examination, performed at once, or after a
long delay, showed generalized internal tuberculosis.
When the chest is extensively affected, the symptoms are those of
broncho-pneumonia or heaves (broken wind), there is hurried breathing
with paroxysmal cough sometimes dry and wheezy, at others moist or
mucous, a double lift of the flank in expiration, and a muco-purulent
discharge from the nose, sometimes streaked with blood. Auscultation
detects a varying force of the respiratory murmur at different points,
with more or less wheezing. Blowing and other sounds conveyed to the ear
through the solidified lung tissues are more rare or less marked.
Percussion may show general resonance, encreased at emphysematous
points, and diminished in small circumscribed areas, the seats of
tubercle or consolidation. There are of course the attendant debility,
inappetence, fever and steadily advancing emaciation. In some cases the
enlarged tracheo-bronchial glands are seen to bulge forward between the
two first ribs, and by the sides of the trachea. Stocking of the limbs
is frequent.
Abdominal tuberculosis is most common in the young foal and when not
secondary, may be due to feeding on tuberculous milk, especially in
those brought up by hand on cow’s milk. There is debility, emaciation,
anæmia, irregular appetite, digestive disorder, constipation alternating
with diarrhœa, colics, pot-belly, falling in beneath the lumbar
transverse processes, dry, harsh, scurfy skin and advancing marasmus.
Rectal exploration will usually detect the enlarged sublumbar and
mesenteric glands, and the simultaneous manifestations of disease of the
lungs, superficial lymph glands, throat, or bones serve to identify the
disease.
In the advanced stages of tuberculosis in solipeds polyuria is a
frequent phenomenon (Nocard) tending to hasten the general anæmia and
marasmus.
The patient often works for months or years but with gradually
encreasing debility, which is soon fatal after the occurrence of
generalized tuberculosis.
In estimating the nature of the disease, indications may often be drawn
from the environment, feeding, etc. Nocard as the result of a careful
study of the morphology and habits of the bacilli has shown that the
more purely abdominal form of equine tuberculosis is near akin to that
of the chicken, while the pronouncedly pulmonary form resembles the
human type. McFadyean on his part adduces a number of cases of
tuberculosis in horses that had been fed largely on cows’ milk, a most
significant fact considering that such a ration is rare for this animal,
and that few horses contract tuberculosis casually. Exposure therefore
to the sputa of man, of the nasal or bowel products of birds or to the
milk of cows, may suggest the probability of tuberculosis in a horse
with chronic anæmia, debility and wasting.
The discharges from the nose of the affected horse are more available
than those of cattle for examination and experimental inoculation, yet
in many occult cases the diagnosis by tuberculin is the only reliable
resort.