Vertically Transmitted Health Issues in Poultry

In a recent conference presentation, Dr T. Kotaiah of of Indbro Research & Breeding Farms Pvt.Ltd, based in Hyderbad, examined how poultry farmers can help to produce clean and safe food for human beings by addressing key health issues in their birds.
calendar icon 27 April 2012
clock icon 11 minute read

The poultry health situation in the country seems to be good, according to Dr T. Kotaiah, speaking at an international symposium in Hyderabad, India, organised by the Association of Avian Health Professionals earlier this year.

There is over–production everywhere, he continued. The prices have been low due to over–supply, even during the festive season of Christmas and the New Year. All commercial broilers are grown on an ‘all–in, all–out’ basis.

The broiler grow–out results are getting better. Many integrators are claiming an average feed conversion of 1.7 and below. This is due to the availability of better breeds, and better feed. Large feed mills are coming up with feed processing technology. All integrators are shifting to steamed crumble pre–starter, starter and pelleted finisher feed. Highly concentrated pre starter diets are common in spite of their higher cost because they are found to be useful. The marketing age of the broilers has been coming down: 2–kg broilers are being produced in 36 to 38 days when the climate is good.

Big broiler breeder flock owners are going for ‘all–in, all–out’ flocks. The breeder flock sizes are increasing to 30,000 and above. Most of the brooding, growing and laying is being done in cages. Artificial insemination has increased the hatch percentages to above 90 per cent, while the weights of the breeder birds are going up. The mating ability of the males is now hardly an issue.

Major Problems

The major health problem in layers seems to be heavy growing depletion, said Dr Kotaiah. Reports of 40 to 50 per cent losses during growing are not uncommon. There are too many vaccinations during growing. All birds are being vaccinated once in five days with one vaccine or the other. It is necessary to have a reexamine the vaccination programme that is being adopted. Should we reduce the vaccinations? Maybe some should be avoided and some should be combined to reduce the stress due to physical handling of the flocks.

Number of vaccines

The number of vaccines given to layers and breeders is high and new ones are still being added. There is a need for the veterinarian to evaluate the programme seriously and look for alternative control measures for some diseases and reduce the vaccinations. Many of the growing problems in layers are associated with excessive vaccination programmes, according to Dr Kotaiah. Repeated handling of birds is affecting the growth of the bird and it must be affecting the development of immunity also.

Vertical Issues

The following are the vertically transmitted issues in poultry. There are three diseases which are transmitted from breeders to their offspring. Taking the lead of vertical transmission, the poultry producers are trying to add value to the product through this route.

The disease problems are bacterial (Pullorum and Gallinarum), Mycoplasma and viral (avian encephalomyelitis – AE and recombinant viruses – ALV).

The value addition can be through:

  1. Maternal antibodies
  2. Nutritional enrichment
  3. Hatchery management to improve the quality of chicks.

Salmonella pullorum and S. gallinarum

Affected birds die of septicaemia. The bacteria gets lodged in the ovary of the survivors and passed in to the egg. Spreads horizontally in the hatcher and brooder. Kills chicks after five days. Mortality can be 80 per cent. Antibiotic injections save the birds but the vertical transmission is not reduced.

Prevention: Keep mortality records (constant mortality in the same pen), PM lesions followed by blood testing and bacterial isolation. Dispose of the positive reactors and test after 21 days. Two consecutive tests should be 100 per cent negative. Keep monitoring for the presence of bacteria in the hatchery and culture the suspected material. If chicks coming from a particular flock start showing regular mortality, the best course would be to liquidate the breeder flock.

Eradication: Total disposal of affected flocks. Total depopulation of the farm. Thorough cleaning of the premises. Keep testing the flocks before laying. Keep strict isolation and watch on the flocks with positive reactors. Cages have less incidence of Salmonella due to reduced reinfection. Nipple drinkers in the place of water channels have reduced the transmission from affected bird to healthy birds. Rodents in the farm can be carriers. Filler flats, equipment and gunny bags spread the infection from flock to flock.

Vaccination: Should be undertaken only when unavoidable, like in valuable breeding stocks. SG9R(1954) produces cellular protection by increasing the number of white blood cells and enhance phagocytosis. Does not produce serum antibodies and will not interfere with testing. Killed bactrins develop quick serum antibodies and stop mortality in the breeder flock but turns the flock 100 per cent positive for plate test. It is dangerous to use killed vaccines in breeders. The immune breeders can still pass on bacteria vertically in low level if the flock gets infected. But this small number of bacteria can multiply horizontally and cause an outbreak in chicks. Quality of the antigen is important. Some antigens have non–specific antigens besides SP and SG. They give false reactions. Dr Kotaiah stated he has come across antigen which showed positive reactors in 100 per cent healthy flocks.


Mycoplasma is a vertically transmitted disease with economical consequences more than mortality. ‘All–in, all–out’ rearing of breeder flocks and good biosecurity have reduced the problem to a great extent. Feeding anti–mycoplasma drugs through feed is helping to suppress the infection. Vaccinations have mixed results. Both live and killed vaccines are available. Producing clean chicks from single age breeder flocks and medication seems to be the best way of eradication.

Avian encephalomyelitis (AE)

Vertically infected day–old chicks show lameness up to 80 per cent with soft bones. AE virus is well tolerated by the birds in the growing stage; layers show a drop in egg production and hatchability when infected. The disease goes unnoticed in broiler breeders. AE is a self limiting disease, the virus becoming neutralised by developing antibodies. The spread is rapid and lasts for two weeks but causes heavy damage in chicks.

Control: Vaccination of breeder flocks during growing (10-14 weeks) with virus or virus analogues is very effective. If 10 per cent of the birds in deep–litter flocks are vaccinated, the live virus spreads very fast and all the birds will be immune in two weeks. All birds are vaccinated in cage rearing and nipple drinkers. Live vaccines are more effective and produce uniform immunity. Killed vaccinations do not create uniform immunity as live vaccines. Killed vaccines are adding to the number of vaccines without added benefit.

Recombinant viruses

Avian leucosis virus is a serious problem in broiler breeders. ALV-J is known to have evolved as recombinant virus. Two half strands of DNA coming from different lines created a new virus. The practice of buying female parents from one source and male from the other has changed. Testing and elimination of the virus–shredders in the primary breeding stocks is the permanent solution. P27 antibody coated Elisa plates are available. The shredding virus of all strains in vaginal or rectal swabs are detected by the Elisa test. Progeny testing of the new crosses for the presence of the disease is essential before commercialisation. Lot of screening at primary breeder level is being done to eradicate this problem. Field cases of ALV are getting rarer.

Value addition to the chicks from the vertical route

The breeder flocks of different age groups have different health status, continued Dr Kotaiah. If all the eggs are handled in the same hatchery on the same day simultaneously, there can be cross–infection at hatchery level. If the large commercial chick flock is a mixture of more than one flock, keeping the breeder flocks isolated becomes meaningless.


The face of broiler production is changing, according to Dr Kotaiah. One business house is taking up vertical integration from grandparents to commercial chicks. If one parent is cared or enriched, the benefit is seen in 150 commercial chicks. The benefits can be vertically transmitted.

  • Produce clean chicks – SG–free, MG–free, ALV–free.
  • Give good levels of maternal antibodies against AE and other viral diseases like IB and ND by booster vaccines to breeder flocks.
  • Early vaccination (In–ovo vaccination on 18th day of incubation) for diseases like Marek’s disease (MD).
  • Added vitamins, protein levels to the breeders will produce healthy chicks even in the beginning of the lay.
  • Control of egg size and shell quality in breeders will avoid problems of blasting in the hatchery.
  • Phase feeding of broiler breeders with higher levels of nutrients when production of the breeder flock is high will result in production of healthy chicks.
  • The concept of ‘one breeder flock – one machine – one day hatch – one commercial farm’ is an important concept in producing excellent broiler grow–out results. The size of the breeder flocks to match the machine and commercial farm capacity should worked out.
  • Single stage settings and ‘All–in, all–out’ hatching in incubator machines will avoid cross infections and add to the uniformity. The incubator machines are to be tuned for this type of hatching. It takes more time to heat up the whole lot of eggs in one machine but saves heating later. The embryos will require more ventilation as they grow towards 18th day.

Hatchery Management

Reduce the ‘hatch window’, i.e. time gap between the first chick and last chick hatched, recommended Dr Kotaiah. Early hatched chicks get dehydrated. The early hatched chicks get stressed in the machines if allowed to stay for longer time. This can be reduced by single stage settings, larger machines. The early hatched chicks will remain non-starters and either die in the first two days or remain behind in growth adding to the flock variation.

Unnecessary use of formalin when the chicks are hatched is known to erode the mucous membrane of the chicks and the make the chicks more vulnerable for infections. Too much handling of chicks at hatchery and delayed dispatches will create stress on chicks.

Plan to reduce the time gap between hatch and placement. Proper preplanning of placement of chicks in the brooder houses and immediate movement of chicks after the hatch also will help in the early start. In extremely cold environments, a separate stage, 'hatch brood’ is being attempted to encourage early feeding and excellent start to the chicks in winter. The chick trays are fitted with feeding and watering and reared for five days in multi-tier controlled environment. The chicks of about 200g transferred to poultry house will have an edge, should reduce the brooding costs in winter and favour FCR.

Early vaccination - in–ovo vaccination – on the 18th day while the eggs are transferred from the setter machine to the hatcher machine is more accurate and can be done mechanically. This saves manual labour and inaccuracies. Bigger hatches have many chicks, require more number of instruments and more people. Machine can handle eggs better than chicks. Machines are more accurate and faster than human beings: 70,000 eggs can be vaccinated per hour by a machine.

Early vaccination for diseases like MD help the vaccine virus to establish faster than the field virus. The live vaccine–maternal antibody interactions on the 18th day of incubation and later need to be examined in detail. Mechanical vaccination is already being used against MD, Newcastle disease, infectious bursal disease (IBD) and coccidiosis. Technically, the following antigen antibody development is known.

Embryo Week 1 Growing Layer
V+ V+ V+ AB- V+ (vertical)
V- V+ V- AB+ V- (horizontal)

The early infected virus is treated as a part of the body by the chick and no antibodies are produced. The virus will exist for a long time. If the chicks born free of virus are infected after birth, the chicks develop antibodies that can neutralise the virus. The above situation can be exploited in designing the vaccination schedules.


Dr Kotaiah concluded that the veterinarian should reexamine vaccination programmes for layers and breeders. The diseases that can be tackled through eradication should be eradicated without vaccination. Combine the vaccines to reduce the number of handlings.

He added that the broiler grow–out period is getting shorter and may settle around 30 days. The attempt should be to avoid any manual handling of broiler chicks for vaccinations. Also avoid use of antibiotics and other medicaments during the growing period in the interest of producing ‘safe food’. The best way, he suggested, will be to prevent vertically transmissible problems in breeders by enriching breeders with nutrients and maternal antibodies; enhancing the hatching practices to avoid cross–contamination and to produce stress–free chicks; where vaccines cannot be avoided, consider administering them in the hatchery and mechanically; and give a clean environment and a good start to the chicks to carry on by themselves, without requiring any manipulation during the 30 days of growth.

These measures will help to produce clean and safe food for human beings, according to Dr Kotaiah.

April 2012

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