moved from the rumen determines the animal 
intake of that forage. Although no relationship 
has been shown from data collected in our lab- 
oratory, confirmation of a direct relationship 
between in vitro fermentation and voluntary 
intake would open a new field in nutrition 
work. This relationship would be especially 
beneficial to range and wildlife research be- 
cause of the difficulty in determining feed in- 
take by range animals. A procedure for deter- 
mining forage intake, based on in vitro and in 
vivo microdigestion, has been described (Van 
Dyne and Meyer 1964). This procedure utilizes 
the conventional method but substitutes micro- 
digestion for conventional macrodigestion de- 
terminations of the forage. 
SUMMARY 
In vivo digestibility experiments are of great 
importance in estimating the nutritive value of 
forages to ruminants. These experiments are 
tedious and require large amounts of forage. 
Because of simplicity, speed, precision, and 
economy, attention has turned to in vitro fer- 
mentation studies for estimating the nutritive 
value of forages. Although some disadvantages 
are apparent, mainly the lack of standardized 
methods, the in vitro fermentation technique 
will be extensively used and may become the 
accepted method for analyzing the nutritive 
value of forage for domestic animals and wild- 
life. 
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