Larvae of cattle grubs also cause losses to the leather industry by dam-aging the hides of cattle. The different kinds of botflies are serious pests because the animals are extremely annoyed while the flies lay their eggs or while they deposit living larvae, as does the sheep botfly. Animals react about the way you would expect if the insects were stinging the host. Actually, however, there is no pain associated with egg laying the animals just have an instinctive fear of the fly that is probably Nature's way of helping them avoid excessive parasitism.
The screwworm fly is about three times as large as the housefly. Eggs are deposited on wounds, and the tiny maggots that hatch feed on the flesh until they are about one-half inch long and as big around as a match. Infested wounds begin bleeding and attract more flies. Thousands of maggots maybe feeding in the wound after a few days. The destruction of tissues and the loss of blood and lymph soon cause the death of the animal if it is not treated. This pest normally occurs only in the southern part of the United States, although local outbreaks occur elsewhere in the summer.
Fleeceworms are caused by flies similar to the screwworm fly. They lay eggs on soiled wool of sheep. The maggots feed on the surface of the skin and cause severe annoyance. Infestations of fleeceworms are often associated with screwworm infestations in sheep. Like the screwworm, the fleeceworms can kill infested animals unless infestations are treated promptly.
Elimination of the cattle-fever tick has solved the most important arthropod disease carrier among livestock.
There are, however, other diseases, among farm animals that are transmitted by arthropods. Anaplasmosis, another important protozoan disease of cattle, may be transmitted in several ways, but ticks, horseflies, and other bloodsucking arthropods can transmit the causative agent. Equine encephalomyelitis, a virus disease of horses, is transmitted by mosquitoes, the principal vector being Culex tarsalis. Blue-tongue, a virus disease of sheep, is carried by culicoides sandflies. Leucocytozoon, a malarialike disease affecting turkeys and ducks, is transmitted by blackflies.
NONINFECTIOUS DISEASES are the ones that are not caused by viruses, microorganisms, parasites, or insects. They are noncommunicable and are commonly found wherever livestock and poultry are raised.
Some of them often are not considered real diseases. But that they are if one defines "disease" correctly: In order to have health, all organs and systems of organs in the animal body must function in unison. When they do not, a disturbance in function may develop and sickness or death may result. Such conditions are common in livestock and poultry on all our farms.
METABOLIC DISEASES are an important group of noninfectious diseases.
Physiology has gone wrong; pathology, or disease, has resulted.
Some of the cells have not carried on their special function, or they have not had normal metabolism in the building up of their protoplasm and the elimination of their waste products. There may have been an interference with the production of cell secretions or the secretion of their products into the body fluids. Chemical substances may be absorbed that stimulate or retard other cells or organs. Chemical substances needed are not produced or are produced in excess; the excess may stimulate or retard other cells or organs. Deficiencies or imbalance of hormones or endocrines may result because there is a disturbance in the glands of internal secretion.
Metabolic diseases are so complex that the explanation of their causes often are only matters of theory.
Some of the important metabolic diseases are ketosis, or acetonemia, of cattle; lambing paralysis of ewes; milk fever of cattle; hypoglycemia of baby pigs; azoturia of horses; blue comb, or pullet disease, of poultry; and some types of sterility.
THE FEED may cause many diseases. Overeating, particularly of unaccustomed feeds, often results in such digestive disorders as bloat, diarrhea, scours, colic, and constipation. Some feeds, such as green legumes, may cause bloat in cattle, sheep, and goats. Nutritional anemia may follow a deficiency in iron, copper, or cobalt in the feed; rickets from a deficiency of phosphorus, calcium, or vitamin D; and the avitaminoses from deficiencies of vitamins.
The feed may cause disease when an imbalance exists in nutrient materials. Metabolic disorders may occur at the same time and complicate matters.
The real cause is often unknown. Research work has been started on the cause of some of these diseases, such as grass tetany of cattle, wheat poisoning of cattle, and urinary calculi, or water belly, of cattle and sheep.
POISON IN FEED may also cause disorders and death.
Grease that contains a poisonous chemical may get into feed when feed mills are lubricated. Many chemicals are used in the manufacture of greases. No mechanical equipment has been developed by which a feed may be pelleted without some of the lubricant going into some of the pellets. This amount is usually too small to produce ill effects in livestock, unless the chemical additive to the grease is very poisonous. Grain that is treated for use as seed may be used later, instead, as feed and produce poisoning.
Almost any chemical eaten in excess even common salt may cause poisoning and varying types of disorders. New agricultural chemicals and paints are used every year, and some of them cause disorders if animals eat or lick them.
FLUORINE POISONING in livestock may result from air pollution in areas surrounding industrial plants that use products containing fluorine. Materials discharged from the factories into the air contaminate forage, which animals may eat. The occurrence and distribution of fluorosis in livestock have coincided with the development and expansion of certain manufacturing processes, mainly in the phosphate and aluminum industries. Cement plants and enameling works may be involved to a limited extent. The fluorine in rock phosphate occurs as a natural fluoride and escapes as dust or gas; in aluminum manufacture, the fluorine is derived from the cryolite and fluorspar used as flux. In the production of cement, the fluorides are carried out mostly as dust.
The feed may cause disease in livestock when some ingredient in it has been processed by some industrially developed method. For example, the trichloroethylene method, which formerly was used in the extraction of soybean oilmeal, caused considerable disease in cattle (called Tesom disease, stockman disease, duren disease, or aplastic anemia) in 1947-1952 in the United States, in 1916 in England, and in 1923-1925 in Germany and the Netherlands.
POISONOUS PLANTS are important causes of animal sickness and losses. Hungry animals that are placed on ranges or pastures, when there is a shortage of feed, or are trailed or moved across ranges are especially likely to eat excessively of poisonous plants, and heavy losses may result.
Poisonous plants are not confined to ranges and pastures. They also grow in meadows, along irrigation ditches, and in hay fields. Some of the common ones are larkspur, lupine, waterhemlock, deathcamus, locoweeds, arrow-grass, and bracken.
Diseases may be caused by some plants that are not ordinarily poisonous but have become so: They have absorbed some chemical from the soil or have built up an excess of some substance during the process of growth. Oat hay from some soils and in some climates has contained excessive amounts of nitrate and has produced heavy death losses in livestock. In some years on some soils, Sudan-grass builds up enough hydrocyanic acid so that it is quite poisonous. Woody aster growing on nonselenious soil is not poisonous, but when it grows on soil high in selenium it absorbs enough selenium to cause it to produce selenium poisoning when it is eaten.
An animal may develop an unusual susceptibility to a substance that is harmless in similar amounts to most animals of the same species. Such an animal is allergic, or hypersusceptible, to the substance. Very likely the substance is a protein one of a group of organic nitrogenous compounds, which are widely distributed in plants and animals and form the chief constituents of the cell protoplasm.
After an animal becomes allergic to a substance, the substance will produce an unusual or exaggerated reaction, called anaphylaxis. A protein from the body cells or body fluids of one species of animals is called a foreign protein when it gets into the blood, serum, or lymph of another species. The same holds true for some of the plant proteins when they get into the blood, serum, or lymph of an animal. Thus some animals may become sensitized to a foreign protein in some plants when they eat them and later show allergic reactions.
INSECTICIDES, herbicides, and fungicides, when accidentally eaten or improperly used, may cause sickness and death among animals. Such materials, which are used to kill, respectively, insects, plants, and fungi, seldom kill livestock if they are mixed and applied according to the manufacturers' directions.
Eating or ingesting pieces of wire, nails, and other metal objects by cattle is a common cause of loss of health and death. They damage the wall of the stomach and penetrate other organs.
Livestock loss is also caused by external mechanical injury.
Tumors are another important and common cause of noninfectious diseases of livestock and poultry.
These and some of the other causes of noninfectious diseases are discussed in later sections.
H. W. SCHOENING retired in 1955 after 48 years of service in the Department of Agriculture. At that time he was assistant to the chief of the Animal Disease and Parasite Research Branch. He was chief of the Pathological Division of the former Bureau of Animal Industry for 20 years.
BENJAMIN SCHWARTZ has been engaged in n parasitological research since 1915. He was chief of the Zoological Division of the Department's former Bureau of Animal Industry from 1936 to 1953 and professor of parasitology in the University of the Philippines from 1921 to 1923. He became staff assistant and consultant in parasitology in the Animal Disease and Parasite Research Branch of the Agricultural Research Service in 1954.
E. F. KNIPLING, a graduate of Texas Agricultural and Mechanical College and Iowa State College, became chief of the Entomology Research Branch in 1953. He was formerly in charge of the Insects Affecting Man and Animals Section of the Entomology Research Branch. He has been with the Department of Agriculture since 1931.
AUBREY M. LEE is head of the Noninfectious Diseases Section of the Animal Disease and Parasite Research Branch, Agricultural Research Service. He received his degree in veterinary medicine at Kansas State College in 1922 and has been with the Department of Agriculture since 1935.