Cyanosis refers to a dark bluish or purplish colouration of the skin and mucous membranes in chickens, according to Danny L. Magee and colleagues at Mississippi State University. Dr Magee is Clinical Professor at the Department of Pathobiology and Population Medicine and Director of the Poultry Research and Diagnostic Laboratory.

Cyanotic meat-type broiler breeder males have been seen for years in the commercial poultry industry. It has been hypothesised that this condition may be initiated by some underlying cardiovascular defect or dysfunction, which is then exacerbated later in life due to risk factors such as male feeding programmes, demand for reproductive performance, and/or environmental stressors.

Professor Magee and co-authors explain that the objective of this research project - supported by the US Poultry & Egg Association, was to determine the primary cause of cyanosis in adult male broiler breeders.

This project was primarily designed to evaluate the cardiac function of these broiler breeder males.

Some preliminary tests had indicated that echocardiography may be helpful in this process. Males of three different breed strains from multiple production companies were evaluated over the course of the project. After echocardiography, the males were necropsied and the hearts collected for further histopathological evaluation. Information gathered included body weights; breast fleshing scores; blood parameters such as cholesterol, haematocrits, nitrates; and heart function analysis of the left side of the heart.

A wide variety of quantitative and subjective as well as gross and microscopic evaluations was performed on hearts obtained from normal roosters and roosters manifesting with transitory skin cyanosis or echocardiogram abnormalities.

A number of suggestive but mostly not statistically significant differences were observed between the echocardiogram- ('echo') normal and echo-abnormal groups.

A striking breed difference was noted in the occurrence of left ventricular area dilation as reflected in gross measurements for the ratio of ventricle chamber to total ventricle area. While no hearts in the Breed A group demonstrated a ventricle area ratio above nine per cent, the Breed B and Breed C groups exhibited an incidence in this parameter of 25 per cent or greater.

Conversely, the number of hearts in the Breed A group below a ratio of four per cent was much greater than the other breeds.

The combined evidence of increased left ventricular wall width and an increase in the incidence of left ventricle ratios below four per cent argue for the possible presence of a constrictive form of cardiomyopathy in some birds in this group. Magee and co-authors stress that the clinical or pathological importance - if any - of these breed findings is not known and they may simply reflect breed differences of no major importance.

At the microscopic level, no major differences in routine subjective histopathology were observed between the echo abnormal and normal groups; nor were any remarkable microscopic pathology present.

The initial concerns with cyanosis were that these males may have had a respiratory and/or a circulatory problem. It was found, in evaluation of birds on the farm that higher average body weights and higher average fleshing scores were both associated with lower incidences of cyanosis. Also, higher haematocrits correlated with an increased incidence of cyanosis.

On first impression, the body weight and fleshing data suggest that proper nutrition and feeding management in broiler breeder males is important in the prevention of cyanosis on the farm. Proper feeding management should also reduce the need for males to eat manure.

The researchers say they can only speculate at this point as to whether those preventative practices may actually be improving cardiac function. But without a change in the management practices of feeding these birds, we may continue to see an increase in haematocrits as a response to decreased oxygen carrying capacity of the blood, which compounds the circulatory problems.

Since the project was designed to work with mature broiler breeder males, it is easy to draw conclusions focused on the mature bird. However, the authors cannot exclude the possibility that the body weight and fleshing data are the result of a heart abnormality that was present in these males at a young age rather than the cause of a heart abnormality later in life.

If this were to be the correct conclusion, feeding practices beginning at day one could still help lessen the impact of the abnormality but would be unlikely to correct it. As with other species, added Professor Magee and colleagues, heart health is vitally important for the overall health and well-being of the breeder male.

February 2014