HIGH-INCIDENCE OF CARDIAC-ARRHYTHMIAS IN BROILER-CHICKENS

A study was completed to characterize cardiac arrhythmias in broiler c hickens. The data were collected from 505 (265 males and 240 females) commercial broilers. Electrocardiograph (ECG) readings were obtained f rom all birds between 7 and 9, 21 and 23, and 42 and 44 days of age. F or comparison, ECG recordings were also collected from 180 broiler bre eders at 3 weeks and 8 weeks of age, and from 100 6-week-old Brown Leg horn and 100 6-week-old Barred Plymouth Rock chicks. The measurements included evaluation of heart rhythm, and incidence of ascites and of s udden death syndrome (SDS). Heart arrhythmias in broiler breeders or i n 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 broil er population showed disrhythmia. The incidence was higher in male bro ilers (P < 0.012) in comparison to females. The most frequently observ ed disturbances of the rhythm were ventricular arrhythmias (VA), the m ost common being premature ventricular contractions (PVC). In most cas es PVC occurred as one or two episodes, but in several birds, runs of three or more consecutive PVCs occurred. Unifocal PVCs were considerab ly more frequent than multifocal PVCs. Sustained ventricular tachycard ia (VT) was least frequent. Heart-related mortalities were observed on ly in broiler chickens. There were 23 SDS cases (4.55% of the populati on) and 13 birds developed ascites (2.25% of the population). Male bro ilers 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 bir d that developed ascites had a history of VA, five birds that develope d ascites had a history of conduction block. It has been concluded tha t, compared to other chickens, the hearts of broiler chickens are cons iderably more susceptible to arrhythmias. Cardiac arrhythmias are invo lved in the pathogenesis of SDS and are likely in some cases of ascite s.