作者：Craig, R. A.
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Common Diseases of Farm Animals试读：
PART I.—INTRODUCTORY
CHAPTER I
> GENERAL DISCUSSION OF DISEASE
Disease is the general term for any deviation from the normal or healthy condition of the body. The morbid processes that result in either slight or marked modifications of the normal condition are recognized by the injurious changes in the structure or function of the organ, or group of body organs involved. The increase in the secretion of urine noticeable in horses in the late fall and winter is caused by the cool weather and the decrease in the perspiration. If, however, the increase in the quantity of urine secreted occurs independently of any normal cause and is accompanied by an unthrifty and weakened condition of the animal, it would then characterize disease. Tissues may undergo changes in order to adapt themselves to different environments, or as a means of protecting themselves against injuries. The coat of a horse becomes heavy and appears rough if the animal is exposed to severe cold. A rough, staring coat is very common in horses affected by disease. The outer layer of the skin becomes thickened when subject to pressure or friction from the harness. This change in structure is purely protective and normal. In disease the deviation from normal must be more permanent in character than it is in the examples mentioned above, and in some way prove injurious to the body functions.
CLASSIFICATION.—We may divide diseases into three classes: non-specific, specific and parasitic.
Non-specific diseases have no constant cause. A variety of causes may produce the same disease. For example, acute indigestion may be caused by a change of diet, watering the animal after feeding grain, by exhaustion and intestinal worms. Usually, but one of the animals in the stable or herd is affected. If several are affected, it is because all have been subject to the same condition, and not because the disease has spread from one animal to another.
Specific Diseases.—The terms infectious and contagious are used in speaking of specific diseases. Much confusion exists in the popular use of these terms. A contagious disease is one that may be transmitted by personal contact, as, for example, influenza, glanders and hog-cholera. As these diseases may be produced by indirect contact with the diseased animal as well as by direct, they are also infectious. There are a few germ diseases that are not spread by the healthy animals coming in direct contact with the diseased animal, as, for example, black leg and southern cattle fever. These are purely infectious diseases. Infection is a more comprehensive term than contagion, as it may be used in alluding to all germ diseases, while the use of the term contagion is rightly limited to such diseases as are produced principally through individual contact.
Parasitic diseases are very common among domestic animals. This class of disease is caused by insects and worms, as for example, lice, mites, ticks, flies, and round and flat worms that live at the expense of their hosts. They may invade any of the organs of the body, but most commonly inhabit the digestive tract and skin. Some of the parasitic insects, mosquitoes, flies and ticks, act as secondary hosts for certain animal microorganisms that they transmit to healthy individuals through the punctures or the bites that they are capable of producing in the skin.
CAUSES.—For convenience we may divide the causes of disease into the predisposing or indirect, and the exciting or direct.
The predisposing causes are such factors as tend to render the body more susceptible to disease or favor the presence of the exciting cause. For example, an animal that is narrow chested and lacking in the development of the vital organs lodged in the thoracic cavity, when exposed to the same condition as the other members of the herd, may contract disease while the animals having better conformation do not (Fig. 1). Hogs confined in well-drained yards and pastures that are free from filth, and fed in pens and on feeding floors that are clean, do not become hosts for large numbers of parasites. Hogs confined in filthy pens are frequently so badly infested with lice and intestinal worms that their health and thriftiness are seriously interfered with. In the first case mentioned the predisposition to disease is in the individual, and in the second case it is in the surroundings (Fig. 2).
[Illustration: FIG. 1.—Side and posterior view of bull showing conformation favorable to the development of disease.]
The exciting causes are the immediate causes of the particular disease. Exciting causes usually operate through the environment. With the exception of the special disease-producing germs, the most common exciting causes are faulty food and faulty methods of feeding. The following predisposing causes of disease may be mentioned:
Age is an important factor in the production of disease. Young and immature animals are more prone to attacks of infectious diseases than are old and mature animals. Hog-cholera usually affects the young hogs in the herd first, while scours, suppurative joint disease and infectious sore mouth are diseases that occur during the first few days or few weeks of the animal's life. Lung and intestinal parasites are more commonly found in the young, growing animals. Old animals are prone to fractures of bones and degenerative changes of the body tissues. As a general rule, the young are more subject to acute diseases and the old to chronic diseases.
[Illustration: FIG. 2.—Insanitary yards.]
The surroundings or environments are important predisposing factors. A dark, crowded, poorly ventilated stable lowers the animal's vitality, and renders it more susceptible to the disease. A few rods difference in the location of stables and yards may make a marked difference in the health of the herd. A dry, protected site is always preferable to one in the open or on low, poorly drained soil. The majority of domestic animals need but little shelter, but they do need dry, comfortable quarters during wet, cold weather.
Faulty feed and faulty methods of feeding are very common causes of diseases of the digestive tract and the nervous system. A change from dry feed to a green, succulent ration is a common cause of acute indigestion in both horses and cattle. The feeding of a heavy ration of grain to horses that are accustomed to exercise, during enforced rest may cause liver and kidney disorders. The feeding of spoiled, decomposed feeds may cause serious nervous and intestinal disorders.
One attack of a certain disease may influence the development of subsequent attacks of the same, or a different disease. An individual may suffer from an attack of pneumonia that so weakens the disease-resisting powers of the lungs as to result in a tubercular infection of these organs. In the horse, one attack of azoturia predisposes it to a second attack. One attack of an infectious disease usually confers immunity against that particular disease. Heredity does not play as important a part in the development of diseases in domestic animals as in the human race. A certain family may inherit a predisposition to disease through the faulty or insufficient development of an organ or group of organs. The different species of animals are affected by diseases peculiar to that particular species. The horse is the only species that is affected with azoturia. Glanders affects solipeds, while black leg is a disease peculiar to cattle.
QUESTIONS
1. What is disease?
2. How are diseases classified? Give an example of the different classes.
3. What is a predisposing cause? Exciting cause?
4. Name the different predisposing and exciting causes of disease.
CHAPTER II
> DIAGNOSIS AND SYMPTOMS OF DISEASE
The importance of recognizing or diagnosing the seat and nature of the morbid change occurring in an organ or group of organs cannot be overestimated. Laymen do not comprehend the difficulty or importance of correctly grouping the signs or symptoms of disease in such a way as to enable them to recognize the nature of the disease. In order to be able to understand the meaning of the many symptoms or signs of disease, we must possess knowledge of the structure and physiological functions of the different organs of the body. We must be familiar with the animal when it is in good health in order to be able to recognize any deviation from the normal due to disease, and we must learn from personal observation the different symptoms that characterize the different diseases. Stockmen should be able to tell when any of the animals in their care are sick as soon as the first symptom of disease manifests itself, by changes in the general appearance and behavior. But in order to ascertain the exact condition a general and systematic examination is necessary. The examiner, whether he be a layman or a veterinarian, must observe the animal carefully, noting the behavior, appearance, surroundings, and general and local symptoms.
Before making a general examination of the animal it is well, if the examiner is not already acquainted with the history of the case (care, feed and surroundings), to learn as much about this from the attendant as is possible. Inquiry should be made as to the feeding, the conditions under which the animal has been kept, the length of time it has been sick, its actions, or any other information that may be of assistance in forming the diagnosis and outlining the treatment.
The general symptoms inform us regarding the condition of the different groups of body organs. A careful study of this group of symptoms enables us correctly to diagnose disease and inform ourselves as to the progress of long, severe affections. These symptoms occur in connection with the pulse, respirations, body temperature, skin and coat, visible mucous membranes, secretions and excretions, and behavior of the animal.
The local symptoms are confined to a definite part or organ. Swelling, pain, tenderness and loss of function are common local symptoms. A direct symptom may also be considered under this head because of its direct relation to the seat of disease. It aids greatly in forming the diagnosis.
Other terms used in describing symptoms of disease are objective, which includes all that can be recognized by the person making the examination; indirect, which are observed at a distance from the seat of the disease; and premonitory, which precede the direct, or characteristic symptoms. The subjective symptoms include such as are felt and described by the patient. These symptoms are available from the human patient only.
Pulse.—The character of the intermittent expansion of the arteries, called the pulse, informs us as to the condition of the heart and blood-vessels. The frequency of the pulse beat varies in the different species of animals. The smaller the animal the more frequent the pulse. In young animals the number of beats per minute is greater than in adults. Excitement or fear, especially if the animal possesses a nervous temperament, increases the frequency of the pulse. During, and for a short time after, feeding and exercise, the pulse rate is higher than when the animal is standing at rest.
The following table gives the normal rate of the pulse beats per minute:
Horse 36 to 40 per minuteOx 45 to 50 per minuteSheep 70 to 80 per minutePig 70 to 80 per minuteDog 90 to 100 per minute
In sickness the pulse is instantly responsive. It is of the greatest aid in diagnosing and in noting the progress of the disease. The following varieties of pulse may be mentioned: frequent, infrequent, quick, slow, large, small, hard, soft and intermittent. The terms frequent and infrequent refer to the number of pulse beats in a given time; quick and slow to the length of time required for the pulse wave to pass beneath the finger; large and small to the volume of the wave; hard and soft to its compressibility; and intermittent to the occasional missing of a beat. A pulse beat that is small and quick, or large and soft, is frequently met with in diseases of a serious character.
[Illustration: FIG. 3.—The X on the lower border of the jaw indicates the place where the pulse is taken.]
The horse's pulse is taken from the submaxillary artery at a point anterior to, or below the angle of the jaw and along its inferior border (Fig. 3). It is here that the artery winds around the inferior border of the jaw in an upward direction, and, because of its location immediately beneath the skin, it can be readily located by pressing lightly over the region with the fingers.
Cattle's pulse is taken from the same artery as in the horse. The artery is most superficial a little above the border of the jaw. It is more difficult to find the pulse wave in cattle than it is in horses, because of the larger amount of connective tissue just beneath the skin and the heavier muscles of the jaw. A very satisfactory pulse may be found in the small arteries located along the inferior part of the lateral region of the tail and near its base.
The sheep's pulse may be taken directly from the femoral artery by placing the fingers over the inner region of the thigh. By pressing with the hand over the region of the heart we may determine its condition.
The hog's pulse can easily be taken from the femoral artery on the internal region of the thigh. The artery crosses this region obliquely and is quite superficial toward its anterior and lower portion.
The dog's pulse is usually taken from the brachial artery. The pulse wave can be readily felt by resting the fingers over the inner region of the arm and just above the elbow. The character of the heart beats in dogs may be determined by resting the hand on the chest wall.
RESPIRATION.—The frequency of the respirations varies with the species. The following table gives the frequency of the respirations in domestic animals:
Horse 8 to 10 per minuteOx 12 to 15 per minuteSheep 12 to 20 per minuteDog 15 to 20 per minutePig 10 to 15 per minute
The ratio of the heart beats to the respirations is about 1:4 or 1:5. This ratio is not constant in ruminants. Rumination, muscular exertion and excitement increase the frequency and cause the respirations to become irregular. In disease the ratio between the heart beats and respirations is greatly disturbed, and the character of the respiratory sounds and movements may be greatly changed (Fig. 4).
[Illustration: FIG. 4.—Auscultation of the lungs can be practised to an advantage over the outlined portion of the chest wall, only.]
Severe exercise and diseased conditions of the lungs cause the animal to breathe rapidly and bring into use all of the respiratory muscles. Such forced or labored breathing is a common symptom in serious lung diseases, "bloat" in cattle, or any condition that may cause dyspnoea. Horses affected with "heaves" show a double contraction of the muscles in the region of the flank during expiration. In spasm of the diaphragm or "thumps" the expiration appears to be a short, jerking movement of the flank. In the abdominal form of respiration the movements of the walls of the chest are limited. This occurs in pleurisy. In the thoracic form of respiration the abdominal wall is held rigid and the movement of the chest walls make up for the deficiency. This latter condition occurs in peritonitis.
A cough is caused by irritation of the membrane lining the air passages. The character of the cough may vary according to the nature of the disease. We may speak of a moist cough when the secretions in the air passages are more or less abundant. A dry cough occurs when the lining membrane of the air passages is dry and inflamed. This may occur in the early stage of the inflammation, or as a result of irritation from dust or irritating gases. Chronic cough occurs
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