The abdominal aorta, brachial and iliac arteries, of 8 White Plymouth Rock hens and 8 pit fowl hens were examined histochemically. The purpose being to (1) determine whether arterial anatomical differences exist; (2) compare the vessels of both groups histochemically; (3) uncover differences in predisposition to atherosclerotic plaques and, (4) relate the incidence of plaques to anatomical and histochemical differences.

The iliac tunica media of the pit fowl was found significantly thicker than that of the White Rock. The tunica adventitia of all iliac arteries having no plaques, were significantly thicker than those of both groups with plaques. The mean bores of iliac and brachial arteries were larger in all animals without plaques.

Histochemical examination indicates increased ground substance present in the pit fowl tunica media. Degeneration of muscle, fragmentation of the elastic lamina and elastica interna, and vacuolation of the tunica intima were observed in association with plaque formation.

A 37.5% incidence of abdominal aortic plaques was common to both groups. Brachial arteries were found to have 50% and 16% incidence for pit fowl and White Rock hens, respectively Iliac vessels of pit fowl and White Rock hens had an incidence of 75% and 57%, respectively.

While plaque occurrence was higher in pit fowl, no aortic ruptures have been reported. It is postulated that the anatomical and histochemical differences present in the pit fowl, coupled with thousands of years of selection, reduce or eliminate aortic rupture.