6. Rabbit Management 
Vol. 9 , Mo. 7 
Page 6 
J . A . Bailey 
> 
During the period March 30th to April »9th, 1966, 10 adult male cottontails 
were collected from each of two areas on the University of Illinois Farm near 
Urbana. These animals were examined for parameters of physical condition which 
might be useful in evaluating the incidence of stress in cottontail populations. 
The work was done by Mr. Ray Schroeder, graduate student at the University, who 
has recently been appointed technical assistant on the Survey staff, on a half-time 
basis, to work on the rabbit project. 
Rabbits were collected by trapping on the Orchard area and on the Department 
of Forestry's area on the University Farm. These areas have quite different 
habitats. The Orchard presents more variety in habitat types, having many patches 
of fruit trees, grape arbors, shrubs, and weedy forbs. Much of the Orchard is kept 
mowed. The area used by the Department of Forestry is primarily wooded, containing 
many patches of conifers. Little of this area is mowed and, in general, it provides 
more dense vegetative cover than does the Orchard. 
All rabbits were measured and weighed upon capture. Total length was determined 
by grasping the animal by the head and hind legs, extending the animal, and measuring 
from the nose to the end of the hind feet. A condition index, the ratio of body 
weight (grams) to the cube of body length (decimeters), was calculated for each 
animal. The rabbits were autopsied soon after collection; adrenals and spleens 
were removed, cleaned of associated tissue, blotted on moist paper, and weighed. 
These organs were then fixed for 2-4 days in Orth's solution, rinsed 4-6 hours in 
tap water, and stored in 80 percent alcohol for future sectioning. Cross sections 
of adrenals, 5 micra thick, were mounted on slides and stained. These sections 
were projected upon paper and sketched. The relative areas of cortical and medullary 
tissue in these sections were determined by cutting the sketches from the paper and 
weighing them. A cortex-medulla ratio was calculated from these weights to indicate 
the size of the adrenal cortex relative to the size of the adrenal medulla. 
Results are presented in Table 6. Adult male rabbits from the Forestry area 
had significantly larger and more variable spleen weights than adult males from the 
Orchard. As a result, they also had significantly smaller adrena1-spleen ratios. 
Animals from the forested area also showed significantly larger and more variable 
adrenal cortices, as indicated by the cortex-medulla ratios. There were no 
significant differences between areas in adrenal weights or in condition indices. 
This work has suggested some parameters of physical condition which should be 
examined in future studies of stress in cottontail rabbits. 
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