A consideration of comparative metabolic aspects of the aetiology of sudden death syndrome and ascites in broilers

Sudden death syndrome in broiler chickens: a review on the etiology and prevention of the syndrome

Sudden death syndrome (SDS) is a condition in which apparently healthy broiler chickens die suddenly. There are short convulsions and frantic wing-beating prior to death, and the weight of internal organs is the same as in healthy chickens. The exact etiology of SDS is unknown. Heart problems have been implicated as a potential cause of the disease in broiler chickens. Despite considerable research, effective methods of prevention are still being sought. Furthermore, the prophylactic measures often make production less profitable (reduced body weight gain resulting from restricted feeding) and prolong the growth period. It is necessary to continue research on SDS, in particular on stimulation of the cardiovascular system to reduce the susceptibility of broilers to sudden death syndrome under intensive production systems.

Effects of Dietary L-carnitine Supplementation on Growth Performance, Organ Weight, Biochemical Parameters and Ascites Susceptibility in Broilers Reared Under Low-temperature Environment

The objective of this study was to investigate the effects of L-carnitine on growth performance, organ weight, biochemical parameters of blood, heart and liver, and ascites susceptibility of broilers at different ages reared under a low-temperature environment. A total of 420 1-d-old male Ross 308 broilers were randomly assigned to two dietary treatments with fifteen replicates of fourteen broilers each. Treatment diets consisted of L-carnitine supplementation at levels of 0 and 100 mg/kg. At 11-d of age, low temperature stress was used to increase ascites susceptibility. Blood, heart and liver samples were collected at different ages for analysis of boichemical parameters. The results showed that, there was no significant difference in growth performance with L-carnitine supplementation, but the mortality due to ascites was significantly decreased. Dietary L-carnitine supplementation significantly reduced heart index (HI) and ascites heart index (AHI) on d 21, lung index (LUI) on d 35 and liver index (LI) on d 42. The broilers fed diets containing L-carnitine had significantly lower red blood cell counts (RBC), hemoglobin (HGB) concentration and hematocrit (HCT) on d 42. Dietary L-carnitine supplementation significantly reduced malondialdehyde (MDA) content of heart tissue on d 21 and 35, and significantly increased total superoxide dismutase (T-SOD) and Glutathione peroxidase (GSH-Px) activity of the heart on d 21 and 42. L-carnitine supplementation significantly reduced serum triglyceride (TG) content on d 28 and 35 and serum glucose (GLU) on d 35 and 42, and significantly increased serum total protein (TP) and globulin (GLO) content on d 42. L-carnitine supplementation significantly enhanced liver succinodehydrogenase (SDH), malic dehydrogenase (MDH) and Na⁺-K⁺-ATPase activity on d 28, and tended to reduce the lactic acid (LD) level of liver on d 35 (p = 0.06). L-carnitine supplementation significantly reduced serum uric acid (UA) content on d 28, 35 and 42. Based on the current results, it can be concluded that dietary L-carnitine supplementation reduced organ index, red blood cell counts and hematocrit, enhanced antioxidative capacity of the heart, enhanced liver enzymes activity involved in tricarboxylic acid cycle, and reduced serum glucose and triglyceride. Therefore, it is suggested that L-carnitine can potentially reduce susceptibility and mortality due to ascites.

Ascites in poultry: Recent investigations

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 influences 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 beta agonists and dietary arginine, which act by increasing ventilation and blood flow in the lungs and thus correcting a ventilation/perfusion mismatch. Transient bacterial and viral infections may also influence 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 flock 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 flow velocities in chickens are relatively slow compared with similar regurgitant flows 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 membranes compromising cellular function in a number of body systems. A positive correlation exists between oxidized glutathione concentrations and right ventricular weight ratio. This indicates a failure to cope with oxidative stress at the level of the respiratory membrane. It is not known if it is possible to modulate levels of antioxidants at this location and hence protect the bird. The final description of the ascites aetiology may lie in the concept of a circuit of events between the cardiac, pulmonary and vascular systems that satisfy the metabolic requirements of the bird. A deficit in one of these systems, at a level that prevents adequate compensation from other components, triggers the pathological cascade that results in the end point of clinical ascites.

Intermittent biotelemetric monitoring of electrocardiograms and temperature in male broilers at risk for sudden death syndrome

Biotelemetry was used to acquire electrocardiograms (ECG) and temperature measurements in a study of male broilers at risk for sudden death syndrome (SDS), a fatal condition that may have underlying cardiovascular mechanisms. Day-old (Day 1) Arbor Acres x Arbor Acres male chicks were randomly assigned to two different diets: control (Diet A) and one that contained elements that contribute to SDS (Diet B). The heaviest birds in each group on Day 13 underwent surgery on Day 15 to have transmitters with temperature sensors and ECG electrodes implanted. After surgery, three controls and three implanted birds from each diet group were kept in individual cages and exposed to 23 h of light and 1 h of darkness during each 24-h cycle. Implantation did not affect weight gain between Days 13 and 22 (P = 0.396). Temperature measurements and 1-min ECG were taken every 15 min. Heart rate and heart rate variability were measured from three 2-s segments in two dark and two light period samples during Days 17 to 19. Diet B decreased weight gain (P = 0.045), lowered heart rate (P < 0.0001), and increased internal temperature (P < 0.0001). Heart rate variability was lower during dark versus light periods (P = 0.004), which indicates that the birds rested during the dark periods, but was not affected by diet (P = 0.651). Thus, biotelemetry provided a useful method for intermittent physiological monitoring of poultry on different diets and under changing environmental conditions.

Incidência de Doenças Metabólicas em Frangos de Corte no Sul do Brasil e Uso do Perfil Bioquímico Sanguíneo para o seu Estudo

Esse trabalho foi realizado em granjas de frangos de corte localizadas no estado do Paraná (sul do Brasil). Foram consideradas 450 granjas, perfazendo uma população total de 4,5 milhões de frangos em um período de 6 meses, durante o qual foram registradas a mortalidade total e as mortes devidas a síndromes metabólicas relacionadas com síndrome ascítica e síndrome de morte súbita, entre a 1ª e a 7ª semana de vida. A mortalidade total foi de 4,8%. Desse total, 12,9% foram registrados como mortos compatíveis com síndrome ascítica e 26,4% compatíveis com síndrome de morte súbita. O pico de mortalidade esteve na 5ª semana de idade para a síndrome ascítica e na 6ª semana para a síndrome de morte súbita. Discute-se que a síndrome de morte súbita pode estar incluindo morte súbita por stress calórico. Os perfis bioquímicos do soro sangüíneo mostraram que aves acometidas por sinais compatíveis com síndrome de morte súbita se caracterizaram por hiperproteinemia, hiperlipidemia, aumentos de ácido úrico, fósforo e magnésio. Nesse caso, o perfil revelou também um choque hipovolémico, além de acidose metabólica e distúrbios no metabolismo dos lipídios. O perfil dos frangos acometidos por sinais compatíveis com síndrome ascítica mostrou depressão do metabolismo energético, evidenciado por diminuição dos níveis de glicose, colesterol e triglicerídeos, além de hipoproteinemia e hipocalcemia.

Correlation between heart muscle damage and high-nutrient feed in broiler chickens

One-day-old broiler chickens were given commercial chicken starters during first 4 weeks of growth. The chickens were then divided into two groups: one group was fed commercial intensive growers (control feed), and the other group was fed commercial broiler finishers (high-nutrient feed). Body weights were calculated weekly. At eight weeks old, blood samples were collected and heart tissues were examined histopathologically. Significant increases in body weight as well as pathological findings in the heart muscle and an elevation of serum creation kinase (CK) were observed in chickens fed with broiler finisher. Histopathological changes in heart fiber resembled that of sudden death syndrome, and this heart damage was thought to be related to the increase of CK levels.

Development of an L6 myoblast in vitro model of moniliformin toxicosis

L6 myoblasts were used as an in vitro model to investigate the role of moniliformin and its interaction with monensin in turkey knockdown syndrome and sudden death syndromes in poultry. Cell viability and microscopic and ultrastructural alterations noted in L6 myoblasts cultured in the presence of moniliformin (0.0-0.3 microgram/microliter) were compared to those observed in parallel cultures also containing one of the following compounds: selenium (0-0.004 ng/microliter), thiamine (0-0.3 microgram/microliter), or pyruvate (0-0.46 microgram/microliter). Marked dilation of the RER, membranous whorls, glycogen deposition, membrane-bound cytoplasmic inclusions and necrosis were observed in myoblasts exposed to 0.03-0.30 microgram moniliformin/microliter medium. Supplementation of medium with thiamine and pyruvate, or selenium, provided significant protection to cells exposed to 0.0-0.3 microgram/microliter or 0.0-0.15 microgram moniliformin/microliter, respectively. Dose-dependent differences in protein and ATP production were not detected. Myoblasts grown in medium containing 0-0.15 microgram moniliformin/microliter and 7.5-50.0 microM A23187, beauvericin or monensin had degrees of cytotoxicity similar to parallel cultures receiving only an ionophore. L6 myoblasts were a useful model of moniliformin toxicosis. The findings of this study suggest cytotoxicity due to moniliformin in L6 myoblasts may be due in part to oxidative damage and altered pyruvate metabolism, and that moniliformin does not predispose myoblasts to ionophore toxicosis. This study supports the results of in vivo investigations in poultry that moniliformin and monensin do not act synergistically to induce knockdown or monensin toxicosis.