Poultry Husbandry Chapter IV: Poultry Health Management for Commercial Poultry

Disease Prevention

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 growth.

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 flock management.

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, temperature, etc.).

(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 followed.

(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 buildings).

(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 farms.

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 kidney disease.

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.

Infectious laryngotracheitis (ILT). ILT 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

a) Preventive 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.

b) Therapeutic 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).