Animal disease is a deviation from the normal and is revealed by changes in the animal. Any animal that has a disease will show some abnormality. This change in the animal can be observed from the behavior, structure or function of the animal in question.
A sick animal will look dull and weak (lethargy), stay on its own and will refuse to feed (anorexia). A dairy animal that produces milk will have a drop in the quantity of milk produced.
You can also notice a change in shape in areas of the body structure of a sick animal depending on the part or organ of the body that is affected. These changes can be major or minor depending on the severity of the disease condition and it can also be qualitative or quantitative.
The observable changes seen or noticed when an animal is sick is known as symptoms or clinical signs. There are symptoms or clinical signs that are common to most diseases while some are specific to particular diseases. Some of the common symptoms seen in most diseases include: refusal to eat, fever or pyrexia (increase in body temperature), dullness etc.
The changes observed when an animal is sick is a basis for diagnosis or determining what is causing the sickness in the animal, and diagnosis can be defined as the art and science of determining the nature and causes of diseases and differentiating between diseases.
To begin with, the first thing is to observe the clinical signs presented by sick animal(s) in question
Further to this, conduct laboratory tests to arrive at definitive diagnosis.
Recognition of Sick Animals
Diseases result in a disturbance in the normal behavior, activity or performance of the animal or animals. In most cases you can observe this change in behavior, activity or performance. General signs or symptoms of sick animals are:
Anorexia (inappetence): The animal goes off feed or refuses to eat.
Fever (pyrexia): This increase in body temperature of the animal above normal.
Weakness (lethargy).
Depression.
These symptoms or clinical signs may not all be present in all diseases all the times. For example an animal suffering from helminthosis (worm infestation) may not show fever unless this condition has another concurrent infection.
Factors Affecting the Health Status of Animals
1. Environmental factors
These factors which are physical in nature influence the health status of animals to varying degrees and they cannot be controlled on the field. They can however, be controlled in an animal facility depending on the sophistication of the facility and the species of livestock. These factors are:
Temperature: Animals have the ability to withstand severe temperatures but this will significantly affect productivity if the exposure is for a long period. This is because the animal will become stressed and stress increases susceptibility to disease.
Humidity: High humidity will promote the growth of certain microorganisms like fungus whereas too low a humidity will result in irritation of the mucous membrane. Humidity is important in poultry since they do not have sweat glands and heat is lost through the respiratory tract.
Solar radiation: This also plays a role in increasing the heat load on an animal. This takes on special importance in hot humid zones with the importation of exotic animals or use of exotic semen from temperate countries to upgrade indigenous livestock breeds.
Solar radiation can be a problem in animals without pigmentation. However, the effect of radiation can be minimized by the shaded areas or pens.
Air movement – The extent of air movement can help in heat loss through evaporation and conduction/convention. Air circulation assists in the supply of fresh air and removal of toxic air.
Rain: Heavy rainfall can result in excessive cooling for animals and/or marshy conditions where animals are kept. This can predispose animals to conditions such as foot rot in ruminants. Provision of shelter and good flooring with drainage is the method to guide against this problem.
Climate/Season: In addition to the environmental factors mentioned above, the climate or season the year can influence the health status of an animal by having a bearing on the infectious agents or parasites that predominate at any particular time.
For example, helminth infections are common during the rainy season. This is because temperature and moisture to large extent determines the ability of a parasite to survive outside the host.
2. Management Factors
Hygiene: Good hygienic practices are good means of reducing disease risk within a herd or flock. Simple procedures such as cleaning of where the animals stay or changing of bedding/flooring can help reduce the degree of contamination or parasitism.
Cleaning removes faeces and thus disturbs the normal environment of disease-causing agents such as gastrointestinal parasites by preventing them from completing their life cycle. It is important that feed/water sources are not contaminated.
Nutrition: Adequate feeding of all classes of livestock is important in order to increase disease resistance and achieve maximum production.
Poor nutrition leads to poor health. Because of the poor feed resource base for livestock occasioned by the seasonal feed shortage, grazing livestock experience exacerbated condition when exposed to infectious agents.
It is therefore necessary to provide supplemental feeding to livestock especially during the dry season. For poultry and other classes of livestock, the high cost of feed ingredients can lead to the compounding of feeds low in nutrients.
Type of housing: Different categories of people use different housing types and different methods to raise livestock depending on the species, resource availability and level of education.
The particular housing system and method of raising the animals can influence the rate and severity of an infection especially with parasitic infections.
For ruminants, animals that are housed or confined where pasture growth is suppressed or flooring is intact, and feeding/watering troughs are kept above the floor will be at lower risk of diseases of gastrointestinal parasitism.
Here, absence of pasture makes the environment not conducive for parasite multiplication. For animals on pasture, the level of pasture contamination depends on factors like concentration of animals, duration of time spent by animals on the pasture, climate or weather condition among others.
It is important that the choice of housing and method of raising livestock be such that it decreases the risk of infection or enhances the health status of animals.
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3. Ecology/Pest and Wildlife
Most parasites that transmit diseases utilize intermediate host to complete their life cycle. This intermediate host can be a pest or wildlife. It is therefore essential not to unnecessarily expose livestock to pest and wildlife.
This is the problem with ruminant owned by nomads as close contact between these animals and wildlife leads to exchange of parasites.
4. Introduction of New Animals/Animal Number
There always exists the risk of introducing new parasites into a herd or flock when adding new animals to a herd. This can be problem where replacement animals are bought from the open market or neighbor’s farm.
Any new animal to be added to an existing stock should be quarantined and treated appropriately before addition. The ease and risk disease transmission increases with increase in animal numbers.
Increase in animal numbers increases contact between animals and consequently ease of transmission.
An increase in animal numbers can also lead to an increase in accumulation of faeces within confined areas and this is not good for endoparasitism except where insecticidal ear tags are used.
In poultry, it is advisable to always clean and disinfect houses before bringing new birds or allowing the house/pen to be empty for some time.
Classification of Livestock Diseases
Livestock diseases can be classified using different criteria depending on what best satisfies the situation under consideration.
Consequently, diseases can be classified based on species of animals (Avian Diseases, bovine diseases, equine diseases, caprine diseases etc.); system of the body affected (Cardiovascular diseases, respiratory diseases, reproductive diseases etc.) and the causative organism.
However, the etiology or causative organism is the most widely used method of classification. Here they are classified as:
Bacterial diseases: example, Anthrax, Mastitis, Salmonellosis, Fowl typhoid, etc.
Viral diseases: example, foot and mouth disease, rinderpest, African swine fever etc.
Protozoan diseases: example, Coccidiosis, Trypanosomoses, Babesiosis etc.
Rickettsial diseases: example, Anaplasmosis, Cowdriosis, Infectious keratoconjuctivitis
Fungal diseases – example, Aspergillosis, Ringworm, Epizootic lymphangitis
Endoparasitic diseases (caused by worms): example, Fascioliosis, Haemonchosis etc.
Ectoparasitic diseases (caused by ticks, lice, fleas): example, Mange, fleabite dermatitis, etc.
Deficiency diseases: Vitamin deficiencies, pregnancy, tooxaemai, etc.
Toxicoses: examples – Nitrate poisoning.
Livestock diseases can also be classified on the basis of disease prevention into six categories which are:
Neonatal diseases: diseases that affect very young animals, mainly diarrhea in nature.
Vector-borne diseases: diseases transmitted by a living vector such trypanosomosis
Soil-borne diseases: disease mostly caused by aerobic and anaerobic spore-forming bacteria (e.g. botulism).
Contact diseases: usually responsible for serious epidemic diseases in livestock in the tropics such as Rinderpest, Foot and Mouth disease etc.
Parasitic diseases: similar to contact diseases examples include haemonchosis, fascioliosis etc.
Nutritional and metabolic diseases.
Animal Disease Diagnosis
To arrive at a diagnosis, you have to get some information or facts about the animal. The information you gather or collect should be as comprehensive as possible and these can be regarded as components of diagnosis. These include:
History taking: This is gathering some information about the animal such as identity of the animal (specie, name or tag no., age, sex, breed, color of the animal etc.), when the animal was first noticed to have changed in behavior or performance, how long this condition has been on etc.
Physical examination: This is done by observing the animal itself for any sign of abnormality, taking the temperature, pulse rate, respiratory rate.
If this done on a farm, it can include looking at the housing and environment where the animal is kept, the type of feed given to the animal or animals etc.
Laboratory examination: This is carried out on samples or materials collected from the animal or the environment where the animal is kept. The sample collected is subjected to several laboratory procedures to detect the presence or absence some disease-causing agents or substances.
Examples of samples collected from a sick animal include blood, faeces, skin scrapings, urine or even organs of a dead animal (especially, where there are many animals on a farm) etc. Also, some part feed of the given to the animal can be collected for laboratory examination.
Laboratory examination of samples collected from sick animals is important in arriving at a definitive diagnosis.
In summary,animal disease diagnosis is to improve animal health not only for production purposes but for the entire area they serve including that of human wellbeing, as some of these animal diseases may be zoonotic in nature.
The practical components of this guide requires that students identify diseases commonly encountered in various livestock animals on the farm they are currently serving and seek for a systematic means of diagnosing disease conditions in them; as well as proffer appropriate treatment/control measures.
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