Poultry Health

Flocks might become infected from a variety of sources. Vertical transmission of viruses, mycoplasma and salmonella, from infected parent flocks to new offspring, whether broilers or layers, has been a common route. Hence, there has been a major effort by breeding companies to eradicate infections where possible or reduce transmission by vaccination and medication.

Mycoplasma infections are a good example of vertical transmission via the egg to the chick and most breeding companies successfully eradicated Mycoplasma gallisepticum (MG) from their flocks of chickens and turkeys. Mycoplasma synoviae (MS) has still persisted in many breeding pyramids (see Table 1) as its clinical significance was considered less important.  Recently, MS has been associated with a variety of conditions, such as egg apex abnormalities, amyloid arthritis, as well as its more commonly associated conditions of airsacculitis and synovitis causing lameness. Salmonella enterica Enteritidis was also associated with vertical transmission and egg contamination became an important human health issue before the introduction of vaccination of layer flocks.

Table 1. Mycoplasma synoviae – vertical transmission - results of seroprevalence (% flocks tested) study in the Netherlands (Feberwee et al, 2008)

Infection from bird-to-bird contact is also important. Where there are multi-age sites of birds, especially in commercial laying flocks, infections can easily circulate between the older and the new incoming flocks. Replacement pullets usually arrive on farm comparatively healthy, having been vaccinated against the most commonly encountered infections.  The pullets then come into contact with a building which has housed a previous flock and may not have been cleaned and disinfected properly and still has live infectious agents in it. There are also neighbouring flocks, which may be excreting virus strains and mycoplasmas, which the pullets have not been vaccinated against and can be transmitted via the air. Transmission by fomites, on peoples’ clothes, boots and hands, via equipment or by rodents and flies can all have a significant role in spreading a variety of infections and challenging the new birds.

The broiler industry has shown how important it is to operate on an ‘all-in, all-out’ basis with good hygiene and cleaning between batches. Ideally, units should be isolated and operated by dedicated staff and equipment and there are good biosecurity measures to keep people, transport and other contact outside the unit. Good rodent control, fly control and protection from wild birds are also important. Rodents can be infected with a variety of bacterial infections such as Salmonella and Brachyspira species; flies can physically carry infections on their feet for a couple of hours and wild birds and migrating birds can transmit a variety of infections, especially avian influenza.

The broiler, layer and turkey breeding industry in the UK have set up good disease control and biosecurity protocols involving feed management too, and have even been able to establish a ‘compartment system’ whereby if the UK does have an outbreak of a notifiable disease (such as avian influenza) and the farms are not directly involved, they can still continue to export.

Free range production

In contrast, the move to free-range production in the UK, whether for layers or broilers does pose some difficulties regarding biosecurity to control contact with other flocks, wild birds, rodents and flies. Direct contact with soil and puddles, and thereby excrement also raises problems with disease control such as parasitic worms and protozoal infections e.g. coccidiosis as well as the birds picking up new bacterial infections such as Brachyspira species. The latter has become widespread in free-range layers in recent years. Vaccines against coccidiosis have been proven effective but worm control requires the use of anthelmintics and spirochaetal infections the use of antibiotics in the main.

Overall, the health and welfare of the poultry industry is critical to its success regarding production performance and profitability. It is the working together of the breeders, producers, veterinarians, nutritionists and the animal health industry, which will help them to achieve their production goals.

Brought to you by Novartis Animal Health,
makers of Denagard