Иностранный язык (английский). Учебное пособие
.pdfstock, the breeder seeks a group of birds that will most closely fit the purpose intended.
Purebred breeding aims to establish and maintain stable traits that animals will pass to the next generation. By «breeding the best to the best» employing a certain degree of inbreeding, considerable culling, and selection for «superior» qualities, one could develop a bloodline superior in certain respects to the original base stock. Such animals can be recorded with a breed registry, the organization that maintains pedigrees and/or stud books. However, single-trait breeding, breeding for only one trait over all others, can be problematic. In one case mentioned by animal behaviorist Temple Grandin, roosters bred for fast growth or heavy muscles did not know how to perform typical rooster courtship dances, which alienated the roosters from hens and led the roosters to kill the hens after reproducing with them.
The observable phenomenon of hybrid vigor stands in contrast to the notion of breed purity. However, on the other hand, indiscriminate breeding of crossbred or hybrid animals may also result in degradation of quality. Studies in evolutionary physiology, behavioral genetics, and other areas of organismal biology have also made use of deliberate selective breeding, though longer generation times and greater difficulty in breeding can make such projects challenging in vertebrates.
Feeding dairy cows
In preparing rations for milking cows many factors should be considered. Rations are to provide carbohydrates in a readily available form, have proper amount of good quality protein, provide sufficient fat and mineral substances and contain the necessary vitamins. To obtain much milk is the aim of every cattleman. That is why the farmers are to supply their cows with nutritious feeds. Cows being on good pastures in summer, little or no additional feed are required. If pastures are of low quality, additional roughages and some grain should be fed to most cows.
During winter legume hay is known to be good roughage for dairy cows. Many dairy farmers provide corn silage or grass silage in addition to hay. High-yielding cows need some concentrated feeds to
91
produce much milk. One can include high-protein feed in the grain mixture for such cows. Roughages of low quality being fed, the proportion of high-protein feed should be increased.
A dairy cow is known to require much water, for milk is about 87 per cent water. Three to four gallons of water are required for each gallon of milk produced by a cow.
Thus, cows being fed properly, all the necessary nutrients will be provided: carbohydrates and fats from grains, proteins from legume hay or protein supplements, minerals from good pasture, and vitamins from, a good mixture of feeds.
Mechanization in livestock raising
Further increase in animal productivity is achieved both by the introduction of new machinery and by wider electrification and automation of different processes on livestock farms.
Some kinds of livestock equipment are almost completely automatic, thus eliminating most of the hand labour. Many farms are using now automatic waterers which provide water to livestock at all times. At the press of the button silage unloaders remove silage from the silo and drop it into the conveyer that carries the silage to the feed troughs. The feeding of grain and hay to dairy cattle has also been almost completely mechanized on some farms. On most farms manure is collected and transported automatically.
Different machines are now being used which permit a better digestion of various feeds by livestock. For instance, grain grinders, feed mixers, forage cutters increase the feeding value of grain, roughages and other feeds. Milk pipelines connected to milking machines carry the milk to milk tanks where it is automatically cooled to the proper temperature.
In some poultry houses time clock devices are installed so that chickens can be fed automatically at the desired time of the day. On many poultry farms eggs are cleaned, graded and packed primarily by automation.
92
Economics of animal breeding
For profitable raising of livestock one should select a breed which is adapted to the purpose for which the animals are to be kept. For milk production a dairy breed should be chosen, not a beef breed. Regardless of the breed the livestock farmers choose, they would be most successful if they kept only the best animals. It is known that there are good and poor animals in every breed.
Feeds are known to make up the largest share of the costs in raising livestock. In the production of meat animals, such as hogs, beef cattle and sheep, feed costs amount to about 80 per cent or more of the total expenses. In egg and milk production they amount to half or more of the total costs. Underfeeding, overfeeding, improper combination of feeds, abrupt changes in feeding and irregular feeding are some of the mistakes that may prove to be costly to livestock raisers.
Great changes have occurred in the cattle feeding industry with the arrival of large commercial feedlots which use industrial methods of management, financing and marketing. The aim of feeding in commercial feed-lots is to simplify the feeding process, thus reducing production costs and labour.
Read the text given below and express your opinion about the advantages and disadvantages of veterinarian profession in the USA
Private Practice. In the United States, approximately 75 % of all veterinarians are in private clinical practice. Of those, about 58 % are engaged in exclusively small animal practice in which they treat only companion animals. Approximately 18 % limit their practice to the care of farm animals or horses. Another 19 % are involved in what is known as mixed (or general) animal practice. Their patients include all types of pets, horses, and livestock. Veterinarians in private clinical practice are responsible for the health of approximately 53 million dogs, 59 million cats. Bird ownership has risen over the past 5 years from 11 million in 1991 to approximately 13 million birds. The number of pleasure horses in the U.S. is about 4.0 million. Other pets
93
such as rabbits, ferrets, guinea pigs, hamsters, gerbils, other rodents, turtles, snakes, lizards, other reptiles and many other animals primarily kept as companion animals. Rabbits and ferrets are owned by 2.3 % of households in the U.S. with a total population of 5.7 million; 4.8 million rodents are owned by 2.3 % of households and 1.5 % of households own 3.5 million reptiles. The fish population is estimated at 55.6 million owned by 6.3 % of households. Veterinarians in private clinical practice work to prevent disease and other health problems in their patients. They examine animal patients, vaccinate them against diseases, prevent the transmission of animal disease to people ("zoonoses"), and advise owners on ways to keep pets and livestock well nourished and healthy. When health problems develop, practitioners must diagnose the problem and treat the patients. Accurate diagnosis frequently requires the use of laboratory tests, radiography (x-rays), and specialized equipment. Treatments may involve a number of procedures including: emergency lifesaving measures, prescribing medication, setting a fracture, delivering a calf, performing surgery, or advising the owner on feeding and care of the patient.
Teaching and Research. More than 3,800 veterinarians are engaged in educating tomorrow's veterinarians at schools and colleges of veterinary medicine. In addition to teaching, veterinary school faculty members conduct basic and clinical research, provide various services to the public, contribute to scientific publications, and develop continuing education programs to help graduate veterinarians acquire new knowledge and skills.Veterinarians in research seek better ways to prevent and solve animal and human health problems. Many problems, such as cancer and cardiovascular disease, are studied through the use of laboratory animals, which are carefully bred, raised, and maintained under the supervision of veterinarians. Laboratory animal veterinarians help select the best animal models for particular research projects and ensure that the animals receive proper care.In addition to developing ways to reduce or eliminate the threat of animal diseases, veterinarians involved in research have made many direct contributions to human health.
Veterinarians were the first to isolate filterable viruses, slow viruses, the first tumor-causing virus, Salmonella species, Brucella
94
species, and other pathogenic agents. They also helped conquer malaria and yellow fever, solved the mystery of botulism, produced an anticoagulant used to treat some people with heart disease, and defined and developed surgical techniques for humans, such as hipjoint replacement and limb and organ transplants.
Regulatory Medicine.Veterinarians in regulatory medicine have two major responsibilities: the control or elimination of certain diseases, and protection of the public from animal diseases that can affect people.Veterinarians who work for the U.S. Department of Agriculture's Food Safety and Inspection Service (FSIS) and for state and municipal food inspection services protect the public from diseased livestock and unsafe meat and poultry. They ensure that food products are safe and wholesome.To prevent the introduction of foreign diseases, veterinarians employed by state and federal regulatory agencies quarantine and inspect animals brought into the United States from other countries. They supervise interstate shipments of animals, test for the presence of diseases, and manage campaigns to prevent and eradicate many diseases, such as tuberculosis, brucellosis, and rabies, which threaten animal and human health. Department of Agriculture veterinarians in the Animal and Plant Health Inspection Service (APHIS) monitor the development and testing of new vaccines to ensure their safety and effectiveness. These APHIS veterinarians are also responsible for enforcing two major humane laws, the Animal Welfare Act and Horse Protection.
Public Health. Veterinarians also work in the area of public health for city, ounty, state, and federal agencies. They help to prevent and control animal and human diseases and promote good health. As epidemiologists they investigate animal and human disease outbreaks such as food-borne illness, influenza, plague, rabies, AIDS, and encephalitis. They evaluate the safety of food processing plants, restaurants, and water supplies. Veterinarians in environmental health programs study and evaluate the effects of various pesticides, industrial pollutants, and other contaminants on people as well as animals.The U.S. Food and Drug Administration
(FDA) employs veterinarians to determine the safety and the efficacy of medicines and food additives.Veterinarians in government and private laboratories provide diagnostic and testing services. Some
95
veterinarians serve as state epidemiologists, directors of environmental health, and directors of state or city public health departments. Veterinarians are also employed by the Agriculture Research Service, Fish and Wildlife Service, Environmental Protection Agency, National Library of Medicine, and National Institutes of Health.
Uniformed Services. Veterinarians serving as officers in the U.S. Army Veterinary Corps are responsible for biomedical research and development. Officers with special training in laboratory animal medicine, pathology, microbiology, or related disciplines are actively engaged in research programs within the military and other government agencies.In the U.S. Air Force, veterinarians serve in the Biomedical Sciences Corps as "public health officers." These officers manage communicable disease control programs at Air Force bases around the world to halt the spread of human immunodeficiency virus (HIV) infection, encephalitis, tuberculosis, and other infectious diseases. They monitor and control insect-borne diseases, such as Lyme Disease and Rocky Mountain Spotted Fever. They also manage influenza, hepatitis, and other human disease vaccination programs.
Private Industry.Veterinarians working in pharmaceutical and biomedical research firms develop, test, and supervise the production of drugs, chemicals, and biological products, such as antibiotics and vaccines for human and animal use. These veterinarians usually have specialized training in pharmacology, virology, bacteriology, pathology, parasitology, toxicology, nutrition, endocrinology, or laboratory animal medicine. Veterinarians are also employed in management, technical sales and services, and marketing in agribusinesses, pet food companies, and pharmaceutical companies.Veterinarians also are in demand for positions in the agricultural chemical industry, private testing laboratories, and laboratory animal medicine. To profitably fulfill the demand for quality food products, veterinarians who have expertise in nutrition and disease control may seek employment in the feed, livestock, and poultry industries.
96
Animal diseases
Disease is the general term for any deviation from the normal or healthy condition of the body. The classification of animal diseases may be approached from several standpoints. Grouping may be based upon:
I. Etiology or Cause. We may divide diseases into two classes: infectious and non-infectious diseases. The first class has two different branches: proper infectious diseases and parasitic diseases. According to the group of pathogens, proper infectious diseases can be divided into diseases caused by a) viruses: measles, influenza, parainfluenza, viral hepatitis, meningitis; b) prions: BSE (bovine spongiform encephalopathy) or mad cow disease, scrapie; c) bacteria: cholera, plague, dysentery, staphylococcal and streptococcal infections, salmonella, meningitis.
Parasitic diseases are very common among domestic animals. This class of diseases is caused by eukaryotic groups of pathogens: a) fungi: aspergillosis, actinomycosis, candidiasis, ringworm, cryptococcosis; b) protozoa: amebiasis, babesiosis, toxoplasmosis, blastocystosis, malaria, balantidiasis, cryptosporidiosis; c) arthropods: insects (lice, flies, fleas) and acarines (mites, ticks); d) 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.
Non-infectious diseases are diseases caused by abiotic agents, such as a) mechanical agents: injuries, overexertion, pressure, friction, impaction by foreign bodies (calculi); b) irregularity in food and water supply; c) chemical causes (poisons); d) thermal agents such as extreme temperature, heat stroke, frost bite, burns, electrical cause, lightning stroke; e) heredity.
II. Duration of the disease. Diseases may be acute or chronic, depending on the duration of their course and the rapidity of intensification and disappearance of the symptoms. “Acute” denotes a disease that is quick and short-lived. “Chronic” denotes a slow longer-
97
lasting condition. The word subacute is used to describe a condition between acute and chronic while a disease, which kills very quickly, like anthrax, is called peracute. The appearance of additional changes that are unrelated to the direct cause of a disease, alongside its principal manifestations, is called a complication. It may arise at the height of a disease or after the principal manifestations have disappeared. Complications are an aggravating factor, and can sometimes lead to an unfavorable outcome. A disease may end in complete recovery, recovery with residual phenomena, stable changes in organs, the occasional development of new manifestations of the disease in the form of long-range sequels.
III. Localization. A general disease is one in which systematic disturbance receives a local change or is early associated with it. Local disease is one in which local change is primary in some organ or part of the body and remains essential and predominant feature throughout. In such a case, it is implied that the disease condition first involves a single organ or tissue. The disease may however be very extensive and yet designated local disease — as in the case of some skin affections.
IV. Number of Affected Animals per Particular Area at a Particular Time.
The diseases can be classified into: sporadic - isolated incident in a single animal; enzootic - disease occurs repeatedly in a particular locality (within 30-mile radius); epizootic - disease that affects a large number of animals in a short period of time in a particular area (larger area than enzootic); panzootic disease that spreads rapidly over a very large area and affects many animals in a short period of time.
V. Contagiosity. Contagious disease is one which is caused by a germ, either bacterium or virus and is usually capable of transmission from one animal to another. As these diseases may be produced by indirect contact with the diseased animal as well as by direct, they are also infectious. Non-contagious disease is one, which is not transferable from one animal to another. Despite a large number of affected animals, the disease can be “non-contagious” (for example, poisoning or dietary deficiency).
98
Parasitic worms
Helminths, also known as parasitic worms, are multicellular eukaryotic invertebrates, which live in the gastrointestinal tract of their host, or may burrow into other organs, such as lungs, heart, kidneys, liver. Helminths important in veterinary medicine are classified into two phyla: Platyhelminthes and Nemathelminthes.
The first group is commonly known as flatworms and is subdivided into cestodes or tapeworms and trematodes or flukes. Nemathelminthes has only one class named nematodes or roundworms.
Cestodes have tape-like, flattened, segmented bodies. Anatomically, they are divided into a scolex, or head, carrying suckers and/or hooks, a neck and a chain of segments called proglottids. They vary in length from 2 to 3 mm to 10 m, and may have three to several thousand segments. Cestodes lack alimentary system, and nutrients are absorbed through the body covering. Body cavity is absent. Tapeworms are hermaphroditic, it means that they have both male and female reproductive organs in the same individual. The adults of most species live only in the intestinal tract of their hosts.
Trematodes are leaf-shaped, unsegmented worms, ranging in length from a few millimeters to 7 to 8 cm. All of them have an oral sucker around the mouth, and another on their ventral surface. They possess an alimentary canal, but it is incomplete. Except for the blood flukes, trematodes are hermaphroditic. Adults of most trematodes live in the gastro-intestinal system, including the liver, gall bladder and bile ducts. Other species parasitize the lungs, the vascular system or the urinary tract.
In contrast to platyhelminths, nematodes are cylindrical rather than flattened, and vary with species from a few mm to more than 50 cm in length. They possess a relatively well-developed complete alimentary canal, with mouth surrounded by lips and armed with teeth or cutting plates, and anus. Most nematode species form two separate sexes, with male and female individuals, males are usually smaller than females. Roundworms may inhabit not only intestinal tract, but also the heart, arteries, lungs. All parasitic worms are obligate parasites, which means that they cannot complete their life cycle
99
without spending some time on their host. The life cycles of helminths are either direct or indirect. The worms with direct life cycles reach maturity and reproduce in a single host that is called definite or final host. Many nematodes have direct life cycles. Typical for flukes and tapeworms indirect life cycles require one or more intermediate hosts in addition to the definite host. Inside these intermediate hosts, the worms complete certain development stages and may reproduce asexually.
In general, helminths exist in three morphological forms – 1) eggs, 2) larval form and 3) adult form (or the worm). Adult worms reach sexual maturity and reproduce inside their host and produce thousands (some species millions) of eggs that are expelled mostly through the feces. Eggs have a strong shell that protects them and let them remain viable for months in soil, fresh water or sewage, and even for years in feces. Larvae hatch out of these eggs and undergo several metamorphoses (molts) depending on the species. The duration of each development stage vary with ecologic and climatic conditions. Knowledge of the life cycle is very important for establishing and managing preventive measures.
Some parasitic worms are host specific, it means that they can complete development only on that particular host species or closely related ones. If infective larvae get into an unsuited host, they will mostly die without causing any harm. But some worm species can be very harmful for such non-final hosts, also called facultative or transport hosts. Typical facultative hosts are small vertebrates such as frogs, lizards, rodents, squirrels. The final hosts get infected by ingestion these facultative hosts.
The signs and symptoms of worm infection, which is known as helminthiasis, depend on a number of factors, including the site of the infestation within the body, the type of worms and the number of them, the immunological response of the animal involved. Some parasitic worms are live threatening for livestock and pets, other species are well tolerated by their hosts without apparent damage. Often helminths are competitors for food, which is virtually "stolen" by the worms living in the host's digestive system. This causes significant productivity losses in livestock: weight loss, insufficient growth, reduced milk or egg production, impaired fertility.
100