With due regard to the necessity of stepping-up production of poultry products, Inspectors of Stock should be vitally concerned in the annual loss of poultry which is usually between 10 and 20 per cent. of adult stock, and about 30 per cent. or more of chickens. Diseases which are often overlooked are Leucosis in adult stock, Avian Encephalomyelitis in chickens, in addition to the more well-known diseases of Pullorum, Coccidiosis and Rickets.
Concerning Leucosis, fowls may waste away, show yellowish or greenish diarrhoea, enlargement of the liver, and the spleen, with discoloured whitish or greyish patches on these organs. As odd fowls may die, e.g., one every day or two, in a flock of several hundred, it does not attract a great deal of notice. If the disease assumes a form where an epidemic of paralysis occurs, it is much more spectacular. Chickens may be affected, when the disease may be confused with Rickets, Encephalomyelitis and other complaints. Sudden deaths in adult stock from Leucosis without premonitory symptoms are usually put down to some other disease. The incidence of Leucosis has been increasing, and the time has come when a careful check up should be made by interested parties in the control of this dribbling economic loss.
To confirm clinical appearances, blood smears of sick birds and tissue specimens preserved in formalin may be forwarded to a laboratory for examination.
The role of the geneticist in the control of disease both of poultry, and, of other animals, has been largely overlooked. With poultry, the genetic approach to disease control has much to recommend it as breeding is so rapid and on a widespread scale. We have much to learn from plant breeders in this connection. e.g., rust resistant wheat. In Leucosis, the major line of attack should be the breeding from mature birds, i.e., first and second year hens and, if possible, mature roosters which is never possible in commercial poultry farming areas, as owners will not hold their male birth for a year "for nothing". In this way birds which are susceptible to the infection, contract the disease, and for the most part die. Any birds which are affected should be disposed of immediately, so that the odd cases which might recover are eliminated before they can be bred from further.
It should be noted that hatcheries are the main means of spreading this disease, as they collect eggs from wherever they can get them during the peak of the hatching season, and with due regard to the rush on the hatcheries this season, it is anticipated that there will be a considerable increase in the incidence of Leucosis.
Differential diagnosis may offer considerable difficulties in the field and one should beware of confusing it with Tuberculosis. The submission of laboratory specimens by Inspectors from the first few cases will rapidly clear up this point.
Avian Encephalomyelitis in Chickens.
This disease is a relative newcomer. The first case was reported in Kingston. Mass., U.S.A., in 1930. It has been observed here since about 1935. It was once known as "Trembles," but it is now recognised that there are two forms, the Clonic or Trembles form and the Paretic form, in which paralysis is the main symptom. In some outbreaks more than half the affected chickens (as confirmed by histologic section) may show the paralysis form alone. It will thus be seen that in this form it may easily be confused with Rickets or even with Perosis.
The disease is caused by a virus which may be transmitted readily from bird to bird, and some evidence indicates that it may be transmitted through the egg. It will be seen that this is a disease of the utmost importance, and suspicious cases should be investigated with all due care. Much work is going on at present; some authors claim that the risk of spread by natural means from chicken to chicken is very slight, but this is definitely doubtful.
Other Mortalities in Chickens.
Hatcherymen rely on more than half the chickens dying which are sent to the country. This is mainly due to faulty breeding equipment, leading to chilling and mass mortality. It is felt that the Australian Hen type of brooder (of iron) can be easily manufactured on the farm and is a suitable improvisation for the country where better types such as the water pipe heating, is not available. An Inspector may be in a position to give advice on the manufacture of such brooders.
Still continues to be common and, in the absence of veterinarians to conduct nation-wide testing, there would seem to be much force in the idea of breeding from survivors of Pullorum Disease outbreaks, as it is well-known that resistance to the disease may be inherited as a genetic factor.
Is a common disease, but can be largely controlled by cleanliness, and the incorporation of five per cent. finely ground sulphur in the mash for a week when the first symptoms of Coccidiosts appear.
It is to be emphasised that breeding from local stock on the farm affords much greater security than introduction of hatchery stock as the latter often introduce diseases.