Cardiovascular System

The four-chambered heart of birds is like its mammalian counterpart, although relative to body size it is much larger and ejects a propor­tionally larger stroke volume. Dorsal and lateral aspects of the heart lie in contact with the liver; other surfaces are surrounded by respiratory elements and air sacs.

Resting heart rates for adult chickens and turkeys are in the range of 200-350 beats per minute, with larger birds having lower rates. A higher resting metabolic rate and higher normal body temperature (41-43°C) for birds contrib­ute to the need to maintain a higher level of resting cardiac performance. Resting blood pressures also tend to be higher in normal, healthy birds than mammals of a comparable size. Abnormally high systemic arterial blood pressures are believed to contribute to the development of dissecting aneurysms or aortic rupture in rapidly growing turkeys. In this condition, a defect develops in the wall of an arterial vessel, often the aorta, and the vessel ruptures at the site of the defect. Massive internal hemorrhage results in sudden death. Increases in arterial pressures are associated with the development of the defect and may contribute to the ultimate rupture of the vessel.

Veins that are usually accessible for veni­puncture include the jugular vein, basilic vein (sometimes called the superficial ulnar vein or simply the “wing vein,” owing to its location on the medial side of the brachium), and the medial metatarsal vein.