Notes for the Poultry Farmer

New Zealand Journal of Agriculture, Volume 69, Issue 5, 15 November 1944, Page 490

Notes for the Poultry Farmer

By

F. C. BOBBY,

Superintendent of the Poultry Industry, Wellington.

Pullorum Disease and Blood-Testing

ALTHOUGH the number of poultry farmers who .have blood-tested their flocks during the present year has been greater than for any previous year, there is still a fairly wide lack of knowledge on this subject. It is particularly desirable that the importance of blood-testing be fully understood in view of the fact that it is one of the obligatory conditions under the New Zealand Poultry Flock Improvement Plan. To understand the position properly it is necessary to review the present knowledge of pullorum as it is affecting poultry in New Zealand. As is generally known, pullorum is a disease which can cause serious mortality among chickens between a day old and approximately two weeks of age. It is an established fact that chickens become infected by this disease through the eggs from which they are hatched; in other words, the germs are in the eggs at hatchingtime, and have come from the birds .laying those eggs. In addition, it m'ust be recognised that uninfected healthy chicks at hatching-time may easily become infected by others carrying the disease ,at a day old. This spread of infection may take place in the incubator as well as under the hovers during the 'early days of rearing. The logical method of controlling and eventually eradicating the disease is therefore to eliminate the hens or pullets which are carrying the germs, and so avoid infected eggs from being hatched. Spread in Adult Stock This raises the first point, which is not always understood. Laying birds infected with pullorum disease rarely show any outward signs of the disease, and may indeed be excellent layers. There are, for instance, no signs of white scour in these birds, and where birds are suffering from a white scour it is extremely unlikely that this is being caused by pullorum disease or bacillary white diarrhoea. A white diarrhoea is caused in the infected chicks, but not in the adult laying stock, although they may be heavily infected with the disease. Adult birds thus infected are referred to as “carriers” or “reactors.” The second name is used because they react to the blood-test and can, in consequence, be recognised as “carriers” of the disease.

A second point of interest refers to the spread of pullorum among adult laying stock. Although not commonly looked upon as a disease of laying birds, pullorum can spread among adult stock and in this way gradually infect a flock, quite apart from any outbreak of trouble which may be experienced with chickens during the rearing season. It should also be remembered that chickens which survive an outbreak of pullorum during the brooding period invariably become “carriers.” A full explanation of the various ways in which the disease can

spread has been given in order that poultry farmers will understand why unexpectedly heavy numbers of “reactors” are sometimes found in their flocks. Laboratory Test Needed There is evidence to indicate that pullorum disease has been present in New Zealand for . some years, but losses among chicks caused by the disease have in many cases been attributed to mismanagement in brooding. Consequently, such chicks have not been sent for a laboratory postmortem examination and the fact that they died from pullorum disease has never been discovered. This raises yet another point which must be stressed. It is not possible for the layman, poultry farmer, or Poultry Instructor to state after, examining a dead chick that it died from pullorum disease. It requires a bacteriological test at a fully-equipped laboratory to diagnose the presence of this disease. It may be added that the test employed is an old-established one, which leaves room for no doubt or expression of opinion as to whether the germ concerned is present or not; the results are clearcut, and full reliance can be. placed on the test. It is possible, of course, for the experienced man investigating chick losses, and taking into consideration the evidence before him, to suspect an outbreak of pullorum, but it is still necessary to obtain confirmation from a laboratory.

More Serious Overseas Evidence has been collected during the past few years indicating that pullorum among poultry in New Zealand is not as virulent as in other poultry-producing countries. For instance, the rate of infection in cabinet incubators is far lower than that experienced in other countries. In the United Kingdom it requires only a limited number of infected chicks in a hatch to cause a serious outbreak of pullorum in all the remaining chicks during the early days of rearing. It will therefore be realised just how fortunate New Zealand poultry farmers are in this respect, particularly with the ever-increasing numbers of cabinet machines now coming into use. There is a further difference between the course of the disease in New Zealand as against that experienced overseas. If, for instance, in England a flock of breeding birds contains, say, 5 per cent, or more “carriers,” there is every possiblity of a serious outbreak of pullorum among the chicks hatched from their eggs however efficient the rearing methods employed may be, On the other hand, in New Zealand chicks from infected hens may show no signs of pullorum disease if well managed under good conditions, but contrarily if badly managed or under poor conditions considerable losses from pullorum may occur. In other words, the disease may remain latent unless the chicks receive some check in the early stages from, perhaps, chilling, poor feeding, etc. This particular feature of pullorum disease in New Zealand has led to many misunderstandings and arguments. It has even been suggested that by encouraging and educating poultry farmers to have good brooding conditions pullorum disease would automatically be kept under control and blood-testing be unecessary. There are, unfortunately, two cogent reasons why this or any similar suggestion cannot be accepted. (1) Pullorum disease is already causing losses among chicks where the brooding conditions and management are efficient. (2) No one is in a position to state that pullorum disease in New Zealand will not increase in virulence if left unchecked in the adult stock. Cause Should be Removed While good brooding methods may minimise chick losses from this disease for the time being, it is logical

to argue-that the root cause of any losses which may occur should be removed. This can be done by systematically blood-testing at least all the breeding stock and, better still, all the adult stock on the farms. To await the time when the disease may have attained the virulence experienced overseas is both a short-sighted and a dangerous policy. Tackle the problem now, with the means already available, and New Zealand poultry farmers may . never experience the real scourge which caused alarming mortalities among chicks in other countries before blood-testing was discovered.

There is one further fallacy which must be exploded. There are still some who think that if their birds are blood-tested once their farms are free from pullorum disease. Unfortunately this is not true. At the time of bloodtesting there is often a small number of birds which, although mildly -infected, do not react to this test. Such birds may later be used as breeders and give chicks which, although infected, rear satisfactorily. These chicks will become reactors in due course at the next season’s test. However, if testing is carried out systematically each season under normal circumstances, the number of reactors per season becomes less, until the disease is either eradicated or at least kept under strict control, when chick losses from pullorum are most unlikely.

Blood-testing involves considerable labour, both for the poultry farmer and for the authorised person carrying out the test. It is therefore desirable that the testing should be done at a time when it will prove most efficient and when it can be handled most conveniently by the poultry farmer. In the first place, the test should be made when the ovaries of the laying birds are active, and it is also recommended that male birds used for. breeding purposes should be included in the test. Even if it is argued that they are unlikely to infect hatching eggs, infected males can spread infection to the females with which they are mated. In practice, experience has shown that male birds do not often react to the bloodtest unless a flock is really heavily infected with pullorum. Scope of the Test The majority of poultry farmers who have accepted the policy of blood-testing their stock annually are confining the test to their breeding stock. In this case it is recommended that the test be made at the time the laying flock is culled and prospective breeders selected for the next breeding season. Normally this is done towards the end of the laying season and before the birds go into a moult.

If tested at this time and the number of reactors exceeds 5 per cent., it then allows the poultry farmer to retest his breeding birds as they come into production after the moult and before the eggs are used for hatching purposes. This is a sound method of obtaining the best protection against pullorum trouble, and should be pursued each year. It must be realised that a single test at the culling season is not sufficient protection against an outbreak of pullorum in the following spring where the test shows a high percentage of reactors. A double test, as suggested, is really essential. Where poultry farmers are prepared to seek the maximum protection from pullorum disease by testing all adult stock on the ’ farm, it. is recommended that pullets be tested just as they are “reddening up.” This can often be done satisfactorily, and with the . least trouble, when the birds are moved into the laying-houses. Where birds are tested as pullets it is seldom necessary to double-test the same birds as hens. Tested as pullets, they then require one further test before being included as hens in the breeding-pen in the following season. Blood-testing involves much additional work for Poultry Instructors, most of which comes within a limited period of time. It is necessary that the work be carefully organised if poultry farmers wishing to blood-

test their stock are to be assisted. For this reason, all poultry farmers requiring the services of a Poultry Instructor for this class of work are urgently requested to make arrangements with the local Instructor well ahead of the time for blood-testing. Looking ahead in this way will be essential if all are to be assisted satisfactorily.

A complete guide to the establishment of a citrus orchard is contained in Bulletin No. 206, “The Citrus-grow-ing Industry,” which is available free from offices of the Department of Agriculture. iitiiiiiiiniiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiitiiiiiiiiiiiiiiiiiifiiii