Feeding and Management

AUBREY M. LEE AND LLOYD A. SPINDLER.

FARMERS combat diseases and parasites when they feed good diets to keep animals in good condition to maintain resistance and manage them in sanitary ways to prevent infection.

Proper feeding is important in maintaining an animal's defenses against disease and parasites. Animals in good condition generally are considered to be more resistant than animals in poor condition. This is especially true of resistance to parasites. It has never been satisfactorily demonstrated by experiments, however, that feeding alone will increase directly an animal's resistance beyond that with which nature has endowed it.

Good nutrition must therefore always be coupled with a degree of cleanliness that prevents acquisition of overwhelming numbers of parasites and germs. Good nutrition, especially if coupled with cleanliness, aids in keeping the resistance of animals at the maximum level provided by nature. It also helps the animal respond properly to immunization.

In general, the best diets are those that contain proteins, vitamins, minerals, and the other essential food elements.

Proteins are especially important, because they are necessary for growth. It is coming to be recognized that animals generally resist parasites better when they are fed diets high in proteins of various types.

Minerals, such as salt, limestone, iron, and copper, also help animals resist the effects of parasites and probably diseases. Parasites such as hookworms and stomach worms injure the lining of the intestinal tract and cause bleeding. This results in anemia. Diets rich in iron, copper, and cobalt may be of value in such cases, because they help correct anemia.

Pastures are important sources of proteins, vitamins, and minerals for livestock. Improved, heavily fertilized pastures may not always provide all the substances needed to maintain a high level of nutrition, however. Animals grazing on pastures of this kind may suffer from dietary deficiencies and have more parasites than those grazing good pastures. Consequently supplemental feeding of animals while they are on pasture is coming to be recognized as highly important from the standpoint of providing adequate amounts of proteins, vitamins, and minerals and controlling diseases, especially those caused by parasites.

Improper feeding may reduce resistance, even if the diet fed is a good one. This happens because lack of feed may lower the level of sugar in the blood in a short time sometimes in 30 hours.

Lack of sugar in the blood may be considered to be a secondary cause of disease since it may predispose the animal to attack by the direct causes bacteria, viruses, parasites, and fungi. Undernourished animals are ready prey to parasites. Once parasites become established, they tend to prevent the animal from making the best use of the food it eats, and it suffers from dietary deficiencies, becomes unthrifty, and is still more susceptible. A vicious cycle thus arises that takes the profit out of livestock raising.

Basic research is needed to determine the precise role of dietary deficiencies and other factors in resistance and susceptibility of livestock and poultry to parasites and transmissible diseases. Largely because of the great cost, not much proved research of that kind has been conducted.

Reports have been published showing that the resistance of experimental animals to tuberculosis is lowered when they are fed diets deficient in one or several nutritional factors. The addition of sodium citrate or sodium glutamate to the diet of mice, for example, Produces a consistent and marked decrease in resistance to this disease. When mice are deprived of food for 30 hours shortly before inoculation with the germs of tuberculosis, their susceptibility is increased. Efforts have been made to modify the resistance of mice to such infections by procedures designed to alter the metabolic processes of the animals, but with little success.

It has been shown that resistance can be decreased by certain types of feeding, but it has not been proved that resistance to transmissible diseases can be increased by feeding. Claims have been made that the use of certain types of feeds will increase the resistance of animals to infectious diseases. For example, it has been stated that increasing the calcium content of the cow's ration will increase the resistance to brucellosis; the feeding of sodium bicarbonate (baking soda) will prevent shipping fever of cattle; and increasing the amount of protein in the ration of swine will increase their resistance to erysipelas. Those claims are false.

In the case of parasites, however, it has been reported that feeds fortified with antibiotics Aureomycin, penicillin, and some others are useful in combating, under certain conditions, the effects of cecal coccidiosis of chickens and infections of ascarids and nodular worms in swine. Such drugs as certain of the sulfonamides and nicarbazin have given good results in checking cecal coccidiosis of poultry, when administered in feed. By and large, infected animals or birds fed the fortified feeds have suffered less from the parasitism and have made better weight gains than parasitized ones on regular diets.

Poor diets or insufficient amounts of good ones are not the sole cause of dietary deficiencies, however. Gastrointestinal disorders of various kinds may interfere with proper digestion and absorption of food. Parasites often cause intestinal disorders which may interfere with digestion. This prevents the animal from utilizing to the best advantage the proteins, vitamins, and minerals, such as calcium, contained in feed and forage and which it needs to maintain health. This is especially true in the case of growing animals, since they require ample amounts of these substances for bone formation and other purposes. Some parasites, such as tapeworms and roundworms, that live in the intestine may even absorb and store up in their own bodies significant amounts of calcium and vitamin B12. This robs the animal of these important substances, lowers its resistance, and makes it susceptible to disease and parasites.

Special attention should be paid to feeding and sanitation of young animals. They are the ones most susceptible to diseases and parasites. They need good feed to meet the demands of growth. Parasites and disease waste feed. Therefore the growing animal that has acquired parasites or is diseased may require more feed than the healthy one.

In summary, it may be stated that animals in good condition generally are believed to be more resistant to infection with diseases and parasites than are animals in poor condition. Proper feeding, housing, handling, and care to maintain animals in good condition therefore are factors that assist in increasing an animal's natural resistance to disease and parasites to the highest point of which it is capable. Debilitating influences that lower the resistance, such as overwork, faulty nutrition, improper care, extreme heat and cold, and bad sanitation are predisposing factors to infection and influence the progress of disease in an infected animal.

AUBREY M. LEE is head of the Noninfectious Diseases Section of the Animal Disease and Parasite Research Branch, Agricultural Research Service.

LLOYD A. SPINDLER was put in charge of the Protozoan Parasite Section, Animal Disease and Parasite Research Branch, in 1955.