Ascites in poultry: Recent investigations

Abstract

In recent years, ascites research has centred on gaining an increased understanding of pulmonary hypertension syndrome together with the potential role of primary cardiac pathologies. The impact at a cellular level of factors which trigger ascites and substances that protect against it has also been documented. Primary pulmonary hypertension has been induced when birds are exposed to hypoxia during incubation. The conditions experienced during this phase of development may impact on the ability of the bird to regulate its basal metabolic rate through endocrine signals controlled by thyroid activity. The extent of ventilation in the lung in¯uences the ability of the bird to oxygenate haemoglobin. Ventilation/ perfusion mismatches may occur prior to or post-hatching. This factor has been studied extensively using the pulmonary artery/bronchus clamp model. At high altitude, a decreased ventilation/perfusion ratio may occur following the effective increase in physiological dead space due to the lowered oxygen tension at the level of the parabronchi. This explains the mechanism by which ascites is triggered by hypoxia in this particular situation. The effects of ascites are ameliorated by the use of b 2 agonists and dietary arginine, which act by increasing ventilation and blood¯ow in the lungs and thus correcting a ventilation/perfusion mismatch. Transient bacterial and viral infections may also in¯uence the induction of pulmonary hypertension. The increases in blood viscosity associated with ascites are most probably a consequence of the condition rather than a cause. A bird may alleviate the effects of pulmonary hypertension by decreasing blood viscosity through inhibition of platelet function, increased erythrocyte deformability and the production of coronary relaxants. Evidence is accumulating that primary cardiac pathology may be associated with a number of ascites cases. Broilers that subsequently develop ascites, exhibit lower heart rates than their normal¯ock mates. Furthermore, during ascites, hypoxic broilers exhibit bradycardia as opposed to the expected tachycardia. In these cases, a tachycardia induced by feed restriction may protect the bird by raising its cardiac output. Right atrio-ventricular regurgitant¯ow velocities in chickens are relatively slow compared with similar regurgitant¯ows induced by pulmonary hypertension in other species. The conduction system in the avian heart is specialized and contains a recurrent bundle branch that innervates the right atrio-ventricular valve, thus initiating active valve closure before right ventricular systole. This predisposes the heart to right ventricular volume overload through a valvular incompetance following a failure of valvular innervation. The resultant elevated diastolic wall stress can trigger the production of angiotensin II and its converting enzyme, which mediate ventricular hypertrophy. Subclinical myocardial damage, irrespective of its cause, can be detected by the presence of troponin T in the blood. Reactive oxygen species may damage cell me...

Cold-Induced Ascites in Broilers: Effects of Vitamin C and Coenzyme Q10

“…Cold temperatures increase the incidence of ascites by increasing both metabolic oxygen requirements and pulmonary hypertension (Bendheim et al, 1992;Julian et al, 1989;Stolz et al, 1992). Oxidative stress due to increased ROS production from mitochondrial electron leak is one of the main causes of the etiology of ascites in poultry exposed to cold temperatures (Currie, 1999). In the present study, mortality due to ascites and the RV/TV ratio in the groups supplemented with Vit.…”

“…According to Currie (1999) the main reasons of the etiology of ascites could be classified as: pulmonary hypertension, cardiac pathologies, and cellular damage due to oxidative stress caused by increased reactive oxygen species (ROS) production. Enkvetchakul et al (1993) verified that chickens with ascites suffered from high oxidative stress.…”

Major differences in the pulmonary circulation between birds and mammals

“…A common disease in broiler chickens apparently associated with rapid gains in weight is Pulmonary Hypertension Syndrome. This is characterized by high pulmonary arterial pressures, ascites, and death, and has been estimated to cost the broiler chicken industry $1 billion per year (Currie 1999). The pathogenesis of this condition is not yet fully understood.…”

Poultry Products with Increased Content of CoQ10 Prepared from Chickens Fed with Supplemental CoQ10

“…Ascites is the most common metabolic disease in chicken and occur worldwide, especially at high altitudes. The disease has a complex aetiology and is predisposed to by reduced ventilation, and respiratory disease (Currie, 1999). The literature data has demonstrated the positive effect of exogenous CoQ 10 in reducing ascites mortality in broilers (Geng et al, 2004).…”