6. Rabbit Management 
Vol, 14, No. 12 
Page 3 
G. B. Rose 
The estimation of the respiration energy of animals in the field has 
proved to be a difficult problem for ecologists. Because it was impractical 
to attempt to determine the energy dynamics of free-living cottontails, it 
was decided to study mature rabbits held in 20- X 20-foot outdoor pens from 
which all vegetation had been eliminated and where energy intake could be 
determined from the amount of a known quantity of feed consumed (MWRL 13(2 )j 4-5. 
When the energy intake and assimilation efficiency for the ration fed are 
known, the amount of energy assimilated can be estimated. (Note: Growth 
energy should also be accounted for—but it is near zero in adult animals.) 
The ^food consumption by the penned cottontails is expressed by the 
equation Y=85»2-.477X|+.929X2^ when X, is ambient temperature in degrees 
Fahrenheit, X« is body weight in ounces, and Y is food consumed, in grams 
(MWRL 14(10):4). 
Using the above equat ion,^when ambient temperature equals 28 C and 
body weight equals 40 ounces, Y=83 grams of food consumed per day. Since 
the digestible energy in a gram of rabbit chow is approximately 2.5 kcal/gram, 
83 grams of food is equivalent to a metabolism of 207 kcal per day. 
In an earlier study, the basal metabolism of adult domestic rabbits, 
ranging in weight from 1 kilogram to 7 kilograms, was measured at temperatures 
in the thermoneutral zone for domestic rabbits, 28 C to 32 C. It was found 
that the linear equation h ta j = 39* 35V/+22.5^ when h is total kilogram 
calories of heat produced (i.e., respiration) per 24 hours and V/ is body 
weight in kilograms. When rabbit body weight is 40 ounces, then, the 
estimated basal metabolism is 67 .I kcal per day. 
Thus, the metabolism of the penned cottontails was 3*09 times the basal 
metabolism of a domestic rabbit of the same weight. Hence, the metabolism 
of free-ranging cottontails should be at least three times the basal metabolism 
of domestic rabbits of the same weight. 
Whether the metabolism of free-ranging rabbits exceeds that of penned 
cottontails is not known. Possibly it does not, for metabolism of cotton rats 
in the field was found to be only 3 to 11 percent greater than (and not signi¬ 
ficantly different from) that of cotton rats in the laboratory, and the 
metabolism of penned rabbits was already 56 percent greater (at one temperature) 
than the metabolism of caged rabbits. 
If the metabolism of free-ranging rabbits exceeds that of rabbits in 
outdoor pens, it is for one or both of two possible reasons. First, there 
could be a greater expenditure of energy for a free-ranging rabbit to search 
for, find, and eat suitable food plants than for a penned rabbit to go to the 
food dish and eat from it. However, because of the common occurrence of plants 
eaten by rabbits, it seems unlikely that the energy cost of the two activities 
would differ greatly. Second, there could be increased energy costs, to free» 
ranging rabbits, resulting from interaction with other individuals of the same 
