ity of the particular plant parts eaten by the 
deer or to their potential contribution toward 
balancing the mixed diet. The futility of nutri- 
tive evaluation of single browse species is 
shown by the results of a Michigan study in 
which aspen and cedar browse were compared 
in digestion trials with deer (Ullrey et al. 
1964). Deer-management experience had indi- 
cated that aspen was heavily utilized. How- 
ever, aspen proved a starvation diet, as indi- 
cated by severe weight loss and negative diges- 
tion coefficients, due to low feed intake during 
the digestion trials. However, it is reasonable 
to assume that aspen is an important dietary 
component, if it is consumed as part of a com- 
plete diet. 
DIGESTIBILITY 
Digestion trials were conducted in which 
various browse species were fed to deer along 
with alfalfa of known digestibility and in 
which their relative digestibilites were mea- 
sured by difference (Dietz et al. 1962). This 
method theoretically should produce more 
meaningful results than single-species trials; 
however, discrepancies between predicted and 
actual digestion coefficients reported by these 
workers raised questions as to whether even 
this method produced results that are worth 
the laborious collection of large amounts of 
browse, which when collected may not be rep- 
resentative of that eaten by free-ranging deer. 
Animal nutritionists have for more than 100 
years been searching for methods of predicting 
feed values from simple laboratory analyses. 
Their progress has been reviewed (Van Soest 
1964). This same author pointed out the im- 
portance of finding methods which will predict, 
in addition to the digestibility of feeds, their 
acceptability or level of voluntary consump- 
tion. 
Various methods of evaluating forages for 
wild ruminants were reviewed (Short 1966). 
The advantages of small-scale laboratory tests 
were indicated; these include in vitro digest- 
ibility measurements which utilize inocula 
from the rumens of freshly killed wild animals 
or from fistulated captive animals. Advantages 
of such methods which require only a few 
grams of forage are obvious, if they can be 
shown to give results that are closely related to 
actual nutritive values. The relative merits of 
in vivo and in vitro forage evaluation methods 
are more thoroughly discussed in other papers 
in these meetings. 
Many workers have studied relationships be- 
tween chemical composition and digestibility of 
forage. Also, various small-scale in vitro diges- 
tion techniques, involving exposure of forage 
samples to fermentation by rumen micro-or- 
ganisms, have been tested (Oh et al. 1966). 
eS 
Following a comparison of these methods, it 
was concluded that several choices are availa- 
ble for comparing digestibilities of forages 
within a species, including simple crude pro- 
tein analysis, but that the twostage in vitro di- 
gestible dry matter method of Tilley and Terry 
(1963) was the method of choice to predict the 
digestibility of all forage species and mixtures 
of species. Other workers have studied the use 
of small-sample zn vivo techniques; here the 
samples are suspended in the rumen of fistu- 
lated animals, and the rate of disintegration of 
the feed is observed (Lusk et al. 1962). These 
methods (in vitro and in vivo) have the advan- 
tage of measuring the digestibility of the feed 
in a biological environment representing rum- 
inal conditions of a healthy animal consuming 
a complete diet. 
SMALL-SAMPLE TECHNIQUES IN 
FORAGE EVALUATION 
Studies are underway in the Department of 
Animal Science, Pennsylvania State Univer- 
sity, University Park, Pa., to compare various 
criteria of feeding value, in order to select a 
small-sample technique which will yield value 
that are reasonably well correlated with actual 
feeding values as measured in digestion trials. 
It is likely that, for purposes of estimating the 
deer-carrying capacity of a given unit of deer 
range, most of the parameters (number of ani- 
mals, yield of forage, portions utilized, etc.) 
entering into the final computation must be at 
best relatively rough estimates; therefore, de- 
termination of feeding values of the many edi- 
ble materials with a high degree of precision 
would be wasted effort. In this respect, our 
needs differ from those of livestock and dairy 
researchers who are working toward maxi- 
mum efficiency of production and therefore, we 
need research methods that will accurately 
measure small differences in feeding value so 
that rations for known numbers of animals, or 
even individuals, can be concocted and fed in 
proper amounts and proportions for most 
efficient and competitive production. Even 
after more than a century of research involv- 
ing many hundreds of workers, the ideal 
method has not been found, and there is still 
disagreement as to which method is best. 
The Penn State Forage Testing Service’s 
functions are to analyze samples of forages 
(hays and silages) sent in by dairymen and 
livestock producers and to recommend supple- 
mental feeding practices for more efficient 
production (Adams et al. 1964). This Service 
uses relationships among crude protein (CP), 
crude fiber (CF), and total digestible nutrients 
(TDN) content to calculate feeding values. 
Based upon data available from more than 700 
forages on which TDN has actually been deter- 
49 
