Comparative Nutritive Values of Forage Species’ 
R. L. COWAN?, J. S. JORDAN, 
J. L. GRIMES’, and J. D. GILL? 
INTRODUCTION 
The game food resource in any type of game 
range has never been scientifically managed. 
Nevertheless, to reach this objective, two main 
courses of action are being pursued. One course 
consists largely of the application of results of 
years of management experience, bolstered by 
the application of research findings (for exam- 
ple, nutrient content of deer forage species) 
when they show promise of solving immediate 
management problems. The greatest obstacle 
to progress is the excessively long period of 
cut-and-try methods needed to determine 
which practices have more than a local appli- 
cation. This course progresses by regular revi- 
sion of short-term management plans. 
The second course consists of a process of 
experimental research that draws largely on 
available basic information on forage species 
and animal nutrition. The determination of nu- 
tritive values of forage species is one of the 
tasks within this research process. As the sub- 
ject of this paper, this task should be placed in 
perspective within the research process. 
The process begins with a record of the dis- 
tribution and abundance of plant species on a 
unit of game range. Other kinds of required in- 
formation are needed in about the following 
order: A list of forage species made up from 
evidence of use by the game species of interest; 
the parts of each forage species used by this 
game species; amounts of these diet compo- 
nents seasonally available on the unit of 
range; seasonal dietary habits and the nutri- 
tional requirements of the game species of in- 
terest; seasonal nutritive value of forage spe- 
cies; methods of forage production; and, a sys- 
tem of forage management that can produce a 
reasonably stable yield of game for recrea- 
tional use. The present paper is concerned en- 
tirely with methods of nutritive evaluation of 
deer forage that are needed to perform a spe- 
cific task within the research process already 
described. 
*This manuscript is published with the approval of 
the Pennsylvania Agricultural Experiment Station as 
article 3540 in the journal series. 
“Cowan is a professor of animal nutrition and 
Grimes is a graduate assistant at the Department of 
Animal Science, Pennsylvania State University, Uni- 
versity Park, Pa. 
* Research Wildlife Biologists, Northeastern Forest 
Experiment Station, Forest Service, USDA, Forestry 
Sciences Laboratory, Warren, Pa., and Morgantown, 
W. Va., respectively. 
48 
NUTRIENT CONTENT OF FORAGE 
Much work has been done in analysis of 
most of the nutrient elements of forage for 
deer. What follow are examples of the variety 
of unrelated pieces of information; from these 
attempts are made to piece together workable 
plans for deer management. 
Chemical analysis of woody browse of sev- 
eral species revealed the occurrence of a 
monthly variation in the nutrient content of 
the previous year’s growth (Hellmers 1940). 
The chemical composition of browse plants 
was found to be influenced by the effects of for- 
est fires (Dewitt and Darby 1955). The time 
and freshness of cutting were shown to influ- 
ence the chemical composition and the accepta- 
bility to deer of twigs from felled hardwood 
trees (Alkon 1961). Seasonal changes report- 
edly occurred in the protein and phosphorus 
content of “portions of the current growth of 
twigs” in Arizona browse plants (Swank 
1956). And the results of chemical analysis of 
“portions of plants normally eaten by deer” led 
to the conclusion that differences in chemical 
composition did not adequately explain the di- 
vision of species into palatable and nonpalata- 
ble groups (Gastler et al. 1951). 
From studies conducted in western Oregon, 
it was shown that there was a relation between 
the crude protein content of browse and deer 
size (Einarson 1946), but it was not stated 
which part of the browse plants was analyzed. 
A study was made of the influence of soil type 
on the “‘available nutrients” in current annual 
growth of selected deer-browse species (Hun- 
dley 1959). Seasonal differences in proximate 
composition were much greater than differ- 
ences due to soil type. 
In all these reports, the authors have inter- 
preted differences in chemical composition to 
be related to differences in nutritive value. 
Such data may be qualitatively useful for as- 
sessment of the general direction of range- 
management practice; however, consideration 
of some fundamental principles of ruminant 
nutrition obviates their usefulness for quanti- 
tative estimation of the carrying capacity of 
deer range. 
First, single species never constitute the en- 
tire diet of wild deer, and the nutritive value 
of any diet component depends upon its rela- 
tionship with all other foodstuffs in the diet. 
Also, analysis of entire plants or of “current 
year’s growth” produces values that may be 
entirely unrelated to either the nutritive qual- 
