High incidence of cardiac arrhythmias in broiler chickens.

A study was completed to characterize cardiac arrhythmias in broiler chickens. The data were collected from 505 (265 males and 240 females) commercial broilers. Electrocardiograph (ECG) readings were obtained from all birds between 7 and 9, 21 and 23, and 42 and 44 days of age. For comparison, ECG recordings were also collected from 180 broiler breeders at 3 and 8 weeks of age, and from 100 6-week-old Brown Leghorn and 100 6-week-old Barred Plymouth Rock chicks. The measurements included evaluation of heart rhythm, and incidence of ascites and of sudden death syndrome (SDS). Heart arrhythmias in broiler breeders or in the two other breeds examined were sporadic. Cardiac arrhythmias in broiler chickens were seen as early as 7 days of age. The incidence of arrhythmias increased with age. At 42-44 days of age 17% of the broiler population showed disrhythmia. The incidence was higher in male broilers (P < 0.012) in comparison to females. The most frequently observed disturbances of the rhythm were ventricular arrhythmias (VA), the most common being premature ventricular contractions (PVC). In most cases PVC occurred as one or two episodes, but in several birds, runs of three or more consecutive PVCs occurred. Unifocal PVCs were considerably more frequent than multifocal PVCs. Sustained ventricular tachycardia (VT) was least frequent. Heart-related mortalities were observed only in broiler chickens. There were 23 SDS cases (4.55% of the population) and 13 birds developed ascites (2.25% of the population). Male broilers had a higher incidence of SDS (P < 0.027) and ascites (P = 0.064) compared to females. Males represented 74% of all SDS cases and 77% of all ascites cases. Whereas three birds that died of SDS and one bird that developed ascites had a history of VA, five birds that developed ascites had a history of conduction block. It has been concluded that, compared to other chickens, the hearts of broiler chickens are considerably more susceptible to arrhythmias. Cardiac arrhythmias are involved in the pathogenesis of SDS and are likely in some cases of ascites.