Occurrence of Shock Disease Among Young Snowshoe Hares. ∗

Abstract

The term, shock disease, 1 has been introduced to describe a disease of snowshoe hares which is associated with the periodic die-off of these animals in the wild. Hares afflicted with this condition have a disturbance of carbohydrate metabolism resulting from liver degeneration. Shock disease has been observed among adult hares in their natural environment, and its presence in hare populations has been demonstrated during the winter months by trapping and holding animals in captivity. Hares taken from certain areas succumbed rapidly from the shock of unnatural conditions, and death was usually accompanied by an extremely low blood sugar level.

The recognition of shock disease among adult hares during winter months raised the question of whether this disease occurs in young hares during the warm months. To gain this information, adult hares were placed in a fenced area of natural habitat in the spring of 1936 and, together with the young subsequently born, were kept under close observation throughout the summer. The fenced area, called “Range A”, consisted of 1.7 acres enclosed with wire of 24 mesh to prevent the escape of young hares. Forty-one females were introduced into this range, most of them in the latter part of April. Six males were entered in April, 3 in May, and 1 in June. Natural forage was available throughout the study, with daily supplemental feeding of carrots, oats, cut aspen; and willow. The young were born in 3 groups: 36 from May 3 to 18; 51 from May 28 to June 26; and 28 between July 1 and 17. Most of them were banded with ear tags at an age of 3 to 5 days, while still in the nest.

Losses, due principally to shock disease, were heavy among both adult and young hares in this range. At the conclusion of the investigation, on November 9, 20 of the 41 females and 8 of the 10 males had died. Only 8 young, 7% of those born, survived the study. The carcasses of 82 young hares were recovered for examination.