Disease Problems of Commercial Pullets: Rearing and Laying
Keith Gooderham, Poultry Health Services
5th May 1999

I must emphasise first of all that most, if not all, disease problems can be prevented. Thus, when a disease occurs, it could be said that the error is not the disease itself but the failure both to anticipate the problem and to prevent it. I therefore want to discuss aspects of disease prevention before progressing onto some of the disease problems encountered.

Day-Old Chick

To answer the question "Which came first, the chicken or the egg?", it is quite clear it was the egg.
For reasons of starting somewhere, I will start with the day-old chick and work backwards.
For a chick to be of the best quality, it must not only look good, but must have several other attributes.
The flock of origin of the chick must have been prepared in a way that the chick has as many protective mechanisms in place to help it to an uneventful start in life.

Disease Control: The parent flock will have been reared and brought into lay under a system of biosecurity and monitoring to ensure that it does not have infections which could be transmitted through the egg to its progeny. Such diseases may be Mycoplasma gallisepticum (Mg), M.synoviae (Ms), Salmonella enteritidis, S.typhimurium, S.pullorum, etc.

Vaccination : The parent flock will have been vaccinated on a programme which
i) affords protection to the flock during lay, thus helping to maintain egg production and egg quality, eg ND, IB, ART, Variant IB,

ii) ensures transmission to the chick of maternal antibodies. These will help protect the chick against disease challenges during its early life, eg ND, IBD (Gumboro).

Nutrition : The parent flock will have been correctly fed to ensure, not only good egg production and hatchability, but that the chick has received the optimal nutrition from its mother for starting life.

Hygiene : The hygiene of the farm, the nest boxes and of egg handling receives attention to avoid dirty eggs and microbial penetration of egg shells.

Correct transport and storage conditions must be planned and executed. Correct hatchery hygiene and hatchery procedures must be in place.

Incubation : Egg age, correct temperature, humidity, turning, etc are important if sub-standard chicks are to be avoided.

Now we have a chick which not only looks good, it is good!

Chick Processing : The newly-hatched chick needs to be taken off at the optimum time and processed quickly. The environment of chick processing should be hygienic and should avoid temperature and air movement shocks. The chick requires Marek's vaccination and sometimes beak-tipping, although this latter procedure is best carried out on the farm after the chick has "started". The holding room should be of a temperature not to overheat the chicks, but the top box of a stack should be lidded. Despatch to the farm should be as soon as possible such that the chick does not spoil before it gets started in its brooding environment.

Farm Preparation :

On the farm, prior to delivery of the chicks, the brooding facility shall have been prepared. This includes a strict programme of cleaning and disinfection after the previous rear as well as a good programme of farm biosecurity.

There are various types of brooding and of house equipment such that they will not be discussed in detail. Suffice it to say that the conditions should be correct for the chick rather than convenient for the staff. These may be described as :
Adequate warmth
Adequate ventilation
A comfortable environment
Adequate water
Adequate feed
Protection from disease
Protection from predators
Protection from excessive competition

Given the correct husbandry, disease problems shoud be minimal. Control of some diseases is helped by vaccination or preventive medication.

Diseases in the First Week :
Yolk-sac Infection
Bacterial Septicaemia
Visceral Gout/Nephrosis
Enterococcal Encephalitis

Diseases in the Second Week :
Chronic Yolk-sac Infection

Later Diseases :
Gumboro Disease

In Lay :
In the laying bird, disease problems may cause drops in egg production, poor quality eggs, illness and/or mortality. It must be remembered that most of these losses are due to conditions other than infectious agents. It is most important that, when some kind of loss occurs, it is described as fully as possible with as many details collected in respect of the flock and farming operation. In an attempt to avoid losses due to infectious agents, a vaccination programme will have been carried out during the rearing period. This will cover viruses such as AE, EDS, ND, ART, IB, Variant IB (eg IB793B). The serological response to these vaccinations may be monitored.

On many occasions, the problem experienced is due to a complex of factors. The best way to control losses is to prevent them by following strict programmes of biosecurity, good husbandry, nutrition and vaccination. What can we do if infectious diseases do occur? Whilst treatment during the rearing period is relatively easy, we now have so few therapeutics for use in laying flocks that effective treatment is difficult to achieve.

Diseases of barn and free-range flocks are likely to be more diverse in nature and more difficult to control. Parasitic diseases become a problem whether mites, lice, worms, or blackhead (histomoniasis). Under such circumstances it becomes even more important to know the farm and its operating programme and to plan a control programme.

Feed can be a problem in terms of introducing disease. Over recent years standards of feed production have improved but as most people do not use heat-treated feed then the possibility of introducing salmonella or other pathogens is real. Again, preventive programmes coupled with monitoring are the best approach.