Probably with poultry more than any other type of animal, the basis of control is prevention. Treatment of individual birds once affected is usually both unsatisfactory and uneconomical.
The maintenance of good health is based in the first instance on breeding from clean healthy stock, as with certain diseases, e.g. fowl paralysis, susceptibility seems to be an inherited factor, whilst with others, e.g. Pullorum disease, the causal organism is transmitted with, among other ways, through infected eggs.
Once we are assured that the eggs are as desired, possessing in addition to the above, good shape, shell texture and weight, they must be correctly incubated and brooded. Incubators should be thoroughly clean to prevent such conditions as "naval infection" and it in desirable to fumigate the incubator after the eggs have been in for it few days, using 17.5 grammes of Potassium Permanganate and 35.0 ml of formalin per 100 cubic feet of air space.
When hatched, correct feeding is necessary to ensure good growth and health and essentials for this are adequate supplies of vitamin A (contained in green feed and cod liver oil), vitamin D (supplied by sunlight and cod liver oil), protein (16-18%), salt (½-1%) and calcium and phosphorus (contained in bonemeal). Clean water should be available, and both food and water should be in containers which prevent soiling by the chickens.
The food factors mentioned are necessary right through the life of the bird, but deficiency of vitamin A (causing pustules in the pharynx and oesophagus, blocking of eyes with caseous material, caseous material in the windpipe and marked changes in the kidneys and ureters) is probably responsible annually for as many deaths as any infectious disease.
Coccidiosis, a protozoan disease which attacks the caeca (blind guts) of chickens when from a week to about ten weeks of age, causing extensive haemorrhage with a fairly heavy mortality, is outstanding as a disease which can only be controlled by prevention. When a bird is infected, the organism multiplies in two ways, forming bodies which again attack the caeca, and other which have thick shells, are highly resistant to drying and which pass out and may remain alive till the following season. Given favourable conditions of moisture and warmth, however, they develop and in a minimum period of about 48 hours are able to infect another chicken. Thus it will be seen that thoroughly cleaning cut the pens at least once in every twenty-four hours would control the disease to a large extent. Feed and water containers should be such as to prevent soiling of the contents, and placing the birds on wire frames lessens the chance of spread of infection. Keeping the birds warm and giving milk powder (up to 40% in the ration) are all that can be done in the way of treatment. Apparatus and accommodation which have housed infected birds should be cleaned with boiling water or with a blowlamp, these being the only effective methods of destroying the oocysts (the little egg-like resistant bodies).
Other diseases are set up by infection from "carriers" when young stock are allowed to run with older birds which have previously passed through a disease outbreak. Such a disease is Infectious Laryngo-tracheitis, and as the "carriers" are usually to all outward appearances normal, and suitable tests are not available for detecting them, the method of control is to prevent any contact (a wire fence between is not sufficient) between the various age classes of birds. Another disease in which "carriers" exist is Pullorum disease, but fortunately they can be detected (and thus eliminated) by use of the agglutination test.
Some diseases rely on vectors for transmission, a typical one being Spirochaetosis or "Tick Fever." The name "Tick Fever" is rather unfortunate, as it has been shown experimentally that the "red mite," Dermanystus gallinae, is capable of transmitting it, and several outbreaks in which only "red mites" have been encountered.
Control of such diseases relies, of course, on elimination of the vectors.
Where it has been found impossible to prevent infection by sanitary measures, vaccines have been elaborated in some instanees, and of these Fowl Pox is the most important. This disease is able to spread long distances by means of mosquitoes, and an efficient vaccine is now available which usually gives a lifelong immunity.
As in other animals, birds may be affected by toxins elaborated outside the body, such as botulism, being susceptible to types A and C but not to type B. Control depends, of course, on preventing access to any putrifying organic matter.
Finally, there are diseases such as fowl paralysis about which not a great deal is known, and control is best attempted by prompt elimination of Infected birds and breeding front strains in which the disease does not occur.