Chronic Respiratory Disease (CRD) in Poultry
By Dr Rob Marshall
Question from Kevin Everson:
What are the best methods to treat and control Chronic Respiratory Disease?
Dr. Rob Marshall’s Answer:
Most poultry breeders know Chronic Respiratory Disease (CRD) as a serious eye infection that is difficult or impossible to cure. This article will describe how best to treat and manage this common ailment.
Mycoplasma gallisepticum is considered the primary cause of Chronic Respiratory Disease (CRD) in poultry. The most common symptoms of Mycoplasma gallisepticum infections in poultry are eye problems and inflammation around the face and cere. Other symptoms include open mouth breathing and gurgling throat sounds.
Disease Stages
There are three stages of the disease:
Stage One
The sudden appearance of wetness around the eye, sometimes referred to as one eye colds, may be due to Mycoplasma gallisepticum infection. One eye colds appear as wetness around the eye with minimal swelling of the eyelids. This type of eye condition may also be the result of stress factors such as drafts or vitamin A deficiency. When detected at this stage, the best treatment method is to apply an appropriate eye cream prescribed by a veterinarian. In most cases, this treatment will clear the eye within 2 days. When no response is seen, the disease is likely to progress to stage two or underlying diseases may be complicating the infection.
Stage Two
As the infection progresses, further symptoms may include swelling of the orbital sinus (“donut” shaped swelling around the eye), pussy eye discharge, sticky eyelids and open mouth breathing. Afflicted birds and the entire flock should be treated when this stage of the disease is seen. Treatment involves the administration of a combination of antibiotics (e.g. doxycycline hydrochloride and tylosine tartrate) into the drinking water for 7 days. An appropriate eye cream is applied to those birds with eye symptoms for 2 days. To accelerate recovery and help reduce the effects of any stressful factors, Turbobooster and E-powder should be mixed into a seed treat each day for 7 days. For stage two of this disease this treatment should give a good response. A poor response indicates that underlying stress factors remain and if not seen to, the disease will progress to stage three.
Stage Three
More advanced symptoms of Mycoplasma gallisepticum infections include a swollen cere, red eyes, cheesy eye discharge, pasted eyelids and an open (gaping) mouth. These more serious symptoms are a good indication that complicated CRD is present and these birds will not respond well to treatment. Those birds with longstanding and complicated Chronic Respiratory Disease should be culled as it is too late for a full recovery and they will spread the disease to other birds in the flock.
The remainder of the flock should receive a 5 day treatment course as described for stage two of this disease.
Birds that have recovered from clinical signs of the disease have some degree of immunity. Such flocks, however, carry the organism and can transmit the disease to susceptible stock by direct contact or by egg transmission to their progeny.
The complicated form of CRD occurs when other underlying diseases are involved. A virus infection called Infectious bronchitis (IBV) is a highly contagious disease causing acute illness, coughing, sneezing and impaired kidney function. IBV may precipitate outbreaks of Mycoplasma gallisepticum, although when present together, mortality in adult flocks is negligible. There is however, a marked reduction in egg laying and mortality in broilers can be high especially during colder months.
E.coli infections have also been found to be a frequently complicating organism while other diseases which may complicate CRD include Mareks disease (Herpes), ILT (infectious laryngo-tracheitis) and Pox virus.
Prevention
It is difficult to prevent infections caused by Mycoplasma gallisepticum because the disease is transmitted by egg and any new birds must be free of the disease. Vaccinations have not proven to be a successful preventative measure because CRD is so often complicated by underlying diseases. Careful management strategies that minimise stress and the ability to determine the stage of CRD are important preventative measures in the treatment and long term prevention of Mycoplasma gallisepticum infections. The attached health programmes help to protect flocks from CRD.