Poultry Husbandry Chapter
IV: Poultry Health Management for Commercial Poultry
Diseases caused by infection
with a living microorganism such as bacteria, virus, mycoplasma, parasite,
etc. are infectious diseases. Most infectious diseases are also contagious,
that is, they spread from one chicken to another but a few, like Staphylococcus
infection, and aspergillosis, are not.
1. Prevention By Sanitation
Sanitation is used to reduce
the numbers of disease organisms which the chicken contacts to the level
where they will no longer cause disease and to provide a clean, healthy
environment. This can be done by cleaning and disinfecting, by adequate
ventilation to reduce the number of organisms in the air and by reducing
contact with other chickens by keeping them in cages.
Sanitation affects all levels
of the birds' environment:
(a) Building and
Equipment: Cages are intended to keep birds out of contact with their
droppings, spilled feed and water, etc. that are a source of bacteria and
bacterial growth. Fly control is important if this method is to be effective.
On floor operations, an adequate amount of dry litter helps control bacterial
At cleanout, blow or spray dust
from walls, ceiling, rafters, fans, etc. Wet down and remove litter, clean
the building and equipment using detergent and water. Follow with a good
disinfectant. A dirt flood cannot be disinfected. Litter should be piled or
spread at least 100m from the poultry buildings (1 km is prefered).
(b) Feed: Between
flocks, clean out feed in the troughs and bins both inside and outside the
building and remove it from the building. It can be held to feed to chickens
of a similar age or sent for reprocessing. Outside storage bins must be
checked to make sure spoiled or moldy feed is not adhering to the inside and
that the bin is empty. Feeders should be constructed and set so that feed is
not spilled or billed out into the litter.
(c) Water: Open troughs
are a source of contamination from the nasal and oral secretion and feces,
etc. and must be cleaned regularly. Nipple drinkers are much cleaner but
pressure must not be too high. Tremendous numbers of bacteria can build up in
ponds and some wells, in water lines, and in drinking cups or troughs, so a
periodic or constant water-sanitizing program and descaling may be necessary.
(d) Air: Clean,
germ-free air is a very important part of a healthy environment. A good
ventilation system to dilute and carry away dust and microorganisms and keep
the pen dry is part of a sanitation program.
(e) The Caretaker:
Workers can carry infection to birds on their hands, clothes, boots, and
equipment. They can spread germs from one group to another on the farm or
bring germs in from outside the farm. If the same person is looking after
more than one building, outer clothing and footwear should be changed between
buildings and hands washed in disinfectant. If possible, separate workers
should care for chicks, young birds and adults.
Good isolation requires
shower-in and no contact with other chickens or other people who have
chickens or work with chickens. Sanitation is a method of eliminating or
reducing the number of disease causing organisms from contacting the birds. Although
one germ may not cause disease and healthy birds may resist hundreds of
germs, sanitation cannot be relied on to control serious contagious diseases.
It must be used in conjunction with isolation and sometimes vaccination for
problems such as Newcastle disease, avian influenza, infectious
laryngotracheitis, fowl pox, etc. However, sanitation is important in
maintaining the general health of a flock and is an important part of good
2. Prevention By Isolation
This method of disease control
is simple. Stop the microorganisms that cause disease from contacting the
chickens. When the microorganisms which cause a disease are eliminated from
an area or country, the disease is said to be eradicated.
Whether or not a disease can be
prevented by isolation depends on:
(a) Where the microorganisms
that cause the disease live. Some organisms (like the ones that cause
necrotic enteritis, staphylococcosis, coccidiosis, E. coli, etc.)
are widespread in the environment and it is difficult to prevent birds from
contacting them. Some organisms are found primarily or only in chickens (sick
birds or healthy carriers) and live outside the bird's body for only a short
time (mycoplasma). Others may live for days, weeks, or months in the
environment, depending on the organism and the conditions (moisture,
(b) The way the disease
organism is spread. Most disease germs are spread by direct contact, that is
bird to bird. If the disease germs get on poultry fluff or small, air-borne
particles, they can be carried by the wind, but this usually only over short
distances. Organisms are frequently spread by mechanical transfer by carrier
objects such as people, eggs, egg cases, trucks, feed, water, rats, dogs,
insects, etc. Two or more separate objects may be involved in the spread of
organisms from one flock to another (chickens to eggs, to egg cases, to
people, back to chickens). Some animals, and certainly wild birds, can become
infected with a disease and spread the germs. Insects are a necessary part of
the spread of some diseases (leukocytozoon, plasmodium, etc.). Some disease
organisms are spread through the egg from the adult to the chick (vertical
spread). Some disease germs are spread venereally or by artificial
insemination in semen (mycoplasma).
Diseases that are easier to
control by isolation are those where the causative agent survives outside the
body for only a short time. If the agent is egg-transmitted, the breeder
flock must also be free of the disease. With some diseases a regular
monitoring program may be required to insure that the flock remains negative.
Isolation is not only the
cheapest but the best way to control many contagious diseases and good
isolation is equivalent to a quarantine.
Important Features Of An Isolation Program
Workers must be trained to
carry out the sanitation and isolation procedures. They must also understand
why the rules are set up and why disease prevention is important.
(a) Have only one age group on
the farm (an all in, all out program). Buildings over 100 meters apart can be
treated as separate units if proper isolation and sanitation procedures are
(b) Obtain chicks or
replacements from a disease-free, adequately isolated, single source or raise
replacements in a different area with separate caretakers.
(c) Have no neighboring poultry
buildings or free ranging chickens within 300 meters.
(d) Clean and sanitize
buildings and equipment between crops. (wet down litter before removal to
protect neighboring poultry and do not store or spread litter near poultry
(e) Screen buildings against
wild birds and keep out rats, cats, and dogs, and control insects. Remove
dead birds from the pens at least twice a day and dispose of sick and dead
birds at least 100m from the poultry buildings. Make sure dogs, cats and wild
birds or animals cannot drag or carry dead chickens onto the farm.
(f) Limit the movement of
workers from one building to another.
(g) Bring in only new or
sterilized egg cases and flats.
(h) Make sure employees do not
keep poultry or pet birds or come in contact with free-range chickens or
their droppings and do not visit other poultry farms.
(I) Keep out visitors
(particularly those who may visit other poultry farms) and provide boots and
protective clothing for persons entering the poultry area.
(j) Disinfect necessary
vehicles (feed trucks etc.) and restrict them to the loading and unloading
areas which should not be near the building entrance. Keep the driver in the
truck or provide boots and coveralls.
(k) Make sure poultry service
crews disinfect equipment, shower, and change clothing before entering the
poultry area (except at cleanout).
(l) Shower and change clothing
after taking chickens to market or meeting with poultry workers from other
3. Prevention By Vaccination
Poultry have a good immune
response to many diseases and to vaccination. They also pass immunity to
offspring through the egg. Breeders require a special vaccination program.
Marek's disease (MD). There are several types of
vaccine. All are live and given by injection. If vaccine is available, all
chicks should receive MD vaccine immediately after hatching. Frequently two
types of vaccine are given together. A second vaccination at a later date is
not required. Chicks must be kept in a clean pen, away from other chickens
for three weeks.
Newcastle disease (ND). There is only one serotype
of NDV so proper vaccination protects against all pathotypes of virus.
Maternal antibody is provided for several days by immune hens. In countries
where velogenic virus is endemic, chicks should be vaccinated before day 7 at
day 21, 35 and 48 using more immunogenic (or virulent) vaccine (LaSota) for
the 3rd and 4th vaccinations. Vaccinations should be repeated at 45 to 60 day
intervals in places where ND is endemic. Properly administered live spray
vaccine is best in adults. Eye drop administration is best for chicks. Either
eye drop or spray can be used after 8 weeks. Vaccine in feed is available for
village flocks. Killed vaccine may be given by injection.
Infectious bronchitis (IB). There are many serotypes of
IBV. Although there is some cross protection, new serotypes appear regularly
that can evade the immunity of some vaccines. Commercial layers should be
vaccinated as recommended locally. Broilers may also require protection. Live
vaccines given in water or by spray are best in growing birds. Killed
vaccines usually in oil may be used for adults. Some serotypes of IBV cause
Infectious bursal disease (IBD). There is one major serotype
of IBDV but there are many pathotypes . As with ND, mild strains of vaccines
will not protect against highly pathogenic strains of virus. Maternal
antibody is provided for 7 to 14 days by immune hens. Where pathogenic
strains of virus are present, moderate strength vaccine should be given at
days 8, 14, and 28. If maternal antibody is not uniform, mild vaccine can be
given at day 1. For maternal immunity killed vaccine in oil (often with ND
& IB) may be given twice at 16 & 18 weeks and may be repeated at 35
to 45 weeks if necessary.
Avian encephalomyelitis (AE). Epidemic tremors. Only
breeders must be vaccinated but egg layers should be done as well to prevent
a drop in egg production. Vaccination is done at about 12 weeks by water or
wing web stab (live vaccine).
Viral arthritis (VA). The arthritic form of
reovirus infection is rare in many countries. Where the disease occurs
broiler breeders should vaccinate twice to provide protection to chicks (live
or killed vaccine).
Mycoplasma gallisepticum (MG). Live MG vaccine is most
effective if it is given to MG negative chickens before they become infected
by the field strain. It provides less protection if given before 4 weeks.
Other programs are available for breeders.
can be prevented by good isolation and sanitation procedures. The vaccine
virus is live and may revert to pathogenic virus and is shed for life by
vaccinated birds (as is field virus by survivors of outbreaks). In endemic
areas breeders and egg type chickens should be eye drop vaccinated when moved
to the laying house. Vaccinate 2 weeks before infection is likely to occur if
growing birds are at risk. In some places broilers are vaccinated in the
drinking water at 3 weeks.
Fowl pox. In endemic areas pox may be
spread by mosquitos and cannot be prevented by isolation. Live pigeon pox (or
other types) vaccine may be given by wing web stab at 8 to 12 weeks. Turkeys
may also require protection.
Egg Drop Syndrome (EDS,
Adenovirus Group III). In
countries where EDS occurs layer and breeder flocks may be vaccinated at
about 16 weeks with killed oil-adjuvant bacterin.
Adenovirus Group I (Inclusion
body hepatitis, IBH).
There are 12 or more serotypes of adenovirus Group I. Subtype 4 and 8 may
cause disease without previous immunosuppression. Live vaccines may have to
be prepared to prevent these infections.
Fowl cholera. On farms or areas where fowl
cholera occurs, birds may be vaccinated with killed or live vaccine. There
are many strains of Pasteurella multocida and autogenous bacterins may be
required for protection.
Infectious coryza. As with fowl cholera. Live
vaccine is not available.
Coccidiosis. Chickens or turkeys raised on
litter or outdoors should be protected by medication until they develop
immunity or by oral vaccination at day 1.
Turkeys may be vaccinated
against Adenovirus Group II (which causes hemorrhagic enteritis (HE) with
live vaccine and against erysipelas with bacterin.
4. Prevention By Medication
medication Some diseases such as coccidiosis, necrotic enteritis and
enterohepatitis can be prevented by medication. Preventive medication is most
useful when protection is only required for a limited time as in broiler
chickens or when immunity does not develop such as in necrotic enteritis.
Coccidiosis. Anticoccidial medication is
very widely used in broilers and is generally used until the birds are ready
for processing. Resistant strains of coccidia may develop and anticoccidials
may have to be switched regularly. Immunity may or may not develop and
anticoccidials that allow immunity are best.
Necrotic enteritis (NE)
(Clostridium perfringens type A). Low level antibiotic in the feed is used to
prevent NE and in Quail ulcerative enteritis (UE) (Clostridium colinum). The
bacteria must be sensitive to the drugs being used and if predisposing
factors such as coccidia infection are present they must also be corrected.
medication Therapeutic medication can be considered preventive when
it is used to control the spread of serious infectious diseases such as
coryza or cholera. Treatment of coryza should not start until 1/3 of the
flock is infected or the disease may recur following treatment.
Some bacteria quickly develop
resistance to medicine and different drugs may have to be used for control.
Virus infections do not usually respond to medicine, although the medicine
may prevent bacterial infection secondary to disease caused by virus.
Medicines given by injection
should not be given into the abdomen or leg. They can be given under the skin
of the back or into the muscle of the breast.
Medicine given in the drinking
water can be poured into the drinkers. In an automatic system they can be
mixed in a large container and run into the system by gravity or a pump.
Medicine can be added to a pressure system with a proportioner. Birds drink
more water in hot weather. The level of medicine must match daily consumption
and should be reduced in hot weather. It could be given for just 8 to 16
hours a day.
Medicine is often added to the
feed at the feed plant. Most preventive medicine is used this way. In a
disease outbreak medicine can be added to the water until medicated feed is
available. Growing birds drink about 3 times as much water compared to the
amount of feed they eat. Adults about 2 times as much (by weight).
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