Victoria Roberts looks at the chicken’s respiratory system and common problems
Birds breathe in a different way from mammals – the air is pushed round the bird’s body in a circle by the ribs and airsacs (think bagipes), with the oxygen being very efficiently extracted by the static lungs. Thus, birds do not have to pause to take a breath in the middle of their song.
As an adaptation for flight, nearly all the bones are hollow for lightness, but they are connected to the lungs, so it can be seen that any respiratory infection is difficult to cure due to the several places that air travels in a bird.
The most common respiratory condition in backyard chickens is mycoplasma infection. Mycoplasma in chickens is not a new disease. There is mention in the old books of similar symptoms from about 100 years ago, generally called roup or a common cold. Treatment tended to be by culling only. This infectious respiratory disease acquired the name ‘mycoplasma’ once the causative organism had been discovered – Mycoplasma gallisepticum.
The disease is becoming more common, with increased stock movements or increased awareness. The incubation period can be as short as a few days and it is very contagious. The birds do not recover from this; it just gets worse with rattley breathing. It appears to thrive in the bird when other pathogens are present, such as E. coli bacteria or Infectious Bronchitis (IB) virus, or if the birds are stressed or debilitated. Factors include nutritional deficiency, high ammonia levels and dust, plus stressors such as changes in the pecking order.
The mycoplasma organism is neither a bacterium nor a virus, and its size is between the two.
Nasal discharge (with a particular sweet smell) causes feathers to become stained as the bird tries to clean its eyes and nostrils. The smell is immediately apparent when entering a hen house. Sometimes, foam in the eye is the first sign, followed by sneezing. Nasal discharge and cool temperatures are protective of the organism, so any sneezing will deposit droplets, which will remain infective for several days. Transmission is also possible through the egg and via mechanical transmission such as on clothes or equipment.
Antibiotic treatment will not completely cure the disease, but will reduce the incidence to a tolerably low level. Tylosin (Tylan Soluble: Elanco) and tiamulin (Tiamutin:Novartis) are licensed for the treatment of mycoplasma, as is enrofloxacin (Baytril Oral 2.5%: Bayer), but the latter should not be used in birds producing eggs for human consumption.
Prevention can include the following:
• Stressors should be kept to a minimum or, if a known stressor such as a show is imminent, advise the use of vitamin supplementation. There are several useful products on the market that contain probiotics and vitamins, administered in the water.
• Suitable disinfectant for huts and equipment, such as Virkon or F10.
• Dust and, especially, ammonia levels need to be kept low. Ammonia paralyses the cilia, small hairs which act like an escalator in the trachea to move normal mucus up before being swallowed. Remaining mucus encourages the growth of bacteria.
• High-quality commercial food appropriate for the stage of growth and the species of bird should be fed.
• Weather changes should be anticipated and steps taken to minimise any effects.
• It is good practice to attend to the youngest birds at the start of the day (ie with clean clothes).
• New stock should be quarantined for 2-3 weeks.
• Birds should not be bought from auctions due to the risk of disease transference.
• If adult stock are kept symptom-free, the risk of passing mycoplasma on through the egg is reduced to a very low level.
• If young stock happen to be exposed to a mild bout of mycoplasma, they will acquire a certain amount of immunity as long as there are no other pathogens present.
• Biosecurity: this means good hygiene and not bringing in disease from elsewhere.
There is a mycoplasma vaccine marketed by Intervet in Europe, but it is not recommended for use in breeding birds. This appears to be because the manufacturers do not know how long the vaccine is effective. With vigilance, mycoplasma can be kept at a low level in backyard flocks thus increasing the welfare of the birds.