Understanding is key to better health

Keeping chickens on a commercial basis can present a number of health challenges, with a broad spectrum of potential causes and symptoms.

So how can producers reach an accurate diagnosis without having to call in a full-time vet? The key, according to Stuart Young from Stuart Young Veterinary Services, is to better understand the birds’ physiology and how diseases affect it.

Speaking at a course supported by the South West Healthy Livestock Initiative and held at Colliton Barton, Broadhembury, Devon, Mr Young said producers could do a lot to fast-track diagnoses and improve treatment success.

“Health planning is very important – it’s about establishing a relationship across the whole farming group, including your vet, staff, nutritionist, pullet or chick supplier, catching and disinfection teams. It has to be a holistic approach.”

Good biosecurity is essential on any unit, said Mr Young. “Microbes can survive outside the bird for years. It is often quoted that just 1g of chicken manure can carry enough viral particles to infect one million birds with avian influenza.”

Producers should consider how disease could be spread on their unit, including through faeces, litter, people, egg trays, other birds, vermin, flies, red mite, feed and wind – and create a health plan to minimise those risks.

Different types of disease

Bacteria and viruses are two key causes of disease in poultry, and are often confused. Bacteria come in a number of different strains, requiring specific antibiotics to kill them. They can survive outside the host animal, and can be prevented with vaccination. Bacterial diseases include E coli, erysipelas and pasteurella.

In contrast, viruses can only reproduce within the living cells of the host, and mutate easily, resulting in a number of different variants of disease, as seen in infectious bronchitis (IB). They can be prevented through vaccination, but there is no real effective treatment for them.

“Antibiotics aren’t always the route out of a problem and may be totally unnecessary,” said Mr Young. “They will be ineffective against viruses, and should not be used as an alternative to good management, vaccination or site hygiene.”

Producers should isolate bacteria strains present in their birds, in conjunction with their vet, to ensure they are using the correct antibiotic. They should always weigh and count the birds to identify the correct dose, and record water consumption to maximise efficacy and minimise the chances of selecting drug-resistant strains.

The immune system

A bird’s immune system develops when they are very young – so it is vital to have healthy reared chicks with a good vaccination programme. There are two primary immune tissues in the chick – the thymus and the bursa of fabricius. Gumboro Disease attacks and destroys the bursa, so chicks which have contracted it will have a very poor immune system.

Secondary immune tissues include: The spleen; bone marrow; lymph nodes; lymphoid tissue in the conjunctiva, bronchi, and gut; and cilia in the trachea. These either act as barriers to infection, or produce white blood cells and antibodies to attack viruses and bacteria.

Aids to diagnosis

Collating all the information available will help your vet to reach a speedy diagnosis and start treatment early. An accurate history is vital – the breed, strain, age and number of birds, type of farming system, feed and pullet supplier, and vaccination history are all useful. Biosecurity information is important, too. Look at the visitor book, feed deliveries, rodent or red mite infestation, wild bird presence and obvious stress factors in the 48 hours before symptoms appear.

Your vet will also want to know what the symptoms are and when you first noticed them. How severe are they, how many birds are affected, have eggs or productivity altered and what is the medication history?

If your vet cannot visit the farm, it may help to take blood samples and swabs to send for laboratory testing. However, producers must be trained by a vet before attempting to do either themselves. For investigating diseases like IB, swabs should be taken from a sample of 10 birds, from areas like the trachea, rear end and internal organs of dead birds. Swabs for PCR testing should have plastic, not wooden, stems, and should be refrigerated and sent within 48 hours, kept cool with an ice pack.

Blood sampling

Ideally, blood samples should be taken at the very onset of symptoms, and again three to four weeks later, to show rising antibody levels to the disease challenge. Statistically, it is best to take samples from 20 birds that are showing signs of illness, unless those tested are kept in isolation for retesting, in which case fewer can be used.

The blood sampling technique is important and should be demonstrated by a vet. A sterile needle and syringe should be used in preference to scalpel blades, which can cause unnecessary damage to the bird. Wiping the area with surgical spirit on cotton wool can help to make the vein stand out, and only about 1ml of blood needs be collected.

Once the sample has been taken, remove the needle from the syringe to fill the sample tube – squirting blood back out of the syringe can damage the blood. Don’t use the same needle on more than 10 birds, as it will start to get blunt. Dispose of the needles in a sharps container and the syringes in a clinical waste bin.

Leave the sample at room temperature for 24 hours to clot – it should separate into red and yellow layers – then refrigerate. If it remains red all the way through, the blood cells have broken down and the sample won’t work. If posting, pathological samples must be packaged according to postage regulations P650 for category B substances. That means triple packaging with absorbent material in case of breakage, and filling out the required paperwork. Discuss dead birds being sent for post-mortem examination with your vet and package them carefully.

Signs of disease

There are many signs of disease in poultry and careful observation can yield clues to their origins. General signs include pale and droopy combs and huddled, quiet birds. Dirty nostrils indicate either dust problems or respiratory disease; swollen ear openings with pus are a sign of pasteurella; and mucky eyes with a visible third eyelid are likely to be infected. Uneven-sized pupils could indicate Marek’s Disease, while diarrhoea is clearly a sign of gut problems.

The respiratory system is particularly sensitive to disease, spreading it rapidly around the body. The trachea has a built-in protection mechanism in hair-like projections called cilia. These line the surface of the trachea and stop foreign material from passing further down the respiratory tract. But management issues like poor ventilation with ammonia build-up; or viral diseases like IB and infectious laryngo tracheitis (ILT) can damage the cilia, making the bird prone to full-blown disease.

Mycoplasma gallisepticum and avian rhino tracheitis (ART) also affect the respiratory system, and are made worse when combined with IB and E coli. Controlling these serious diseases through vaccination and improved biosecurity will therefore minimise the impact of other pathogens that birds will be exposed to.

The best way to achieve a diagnosis is to submit birds to your vet for post-mortem examination – although producers could attend a training course to carry out basic dissections themselves. For example, Pasteurella multocida, which causes sudden death, can be diagnosed from swabs taken in a sterile manner of the heart, liver and lungs. An enlarged spleen can be the result of erysipelas, and tumours are a sign of Marek’s Disease. Worms may be found in the trachea or intestines; and yellow pus in the abdomen indicates egg peritonitis. This common complaint can be triggered by stress, but may also be a consequence of many other disease challenges like IB.

Disease control

Most of the main types of disease are spread through poor biosecurity – vermin, flies and red mite are all common carriers. Sub-standard housing conditions will also make the birds more vulnerable to stress and disease, so getting the basics right and drawing up a flock health plan should markedly reduce the incidence of disease.

However, some diseases will always present a challenge, so understanding the likely symptoms and causes and arming your vet with as much pertinent information as possible, will help to secure an early diagnosis and more effective treatment.

The West Country Layers Association will be holding a conference on 25 May, entitled “2012 and beyond”. Contact Rachel Watkins on 07966 558 386.

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