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Chapter 26 



of digestion is remarkable, however. Evidence suggests that the lower termites 

 comminute wood, transport it to their hind gut where protozoa digest it and 

 metabolize it anaerobically to carbon dioxide, hydrogen, and acetic acid via 

 glucose; acetic acid may then be oxidized by the termite to satisfy its energy 

 needs. Dwell time within the termite is about 24 hours. One could conceive of a 

 wood utilization system in which termites were an intermediate in a protein 

 production system. 



Ruminants such as cattle and sheep require several hours to 2 days for 

 complete passage of food through the digestive system. The rate of passage 

 depends on the amount of fiber in the food and on particle size. Bulky feeds are 

 retained in the rumen until rumination occurs — which often takes place at night. 

 About 1 8 hours is thought to be an average for completion of microbial digestion 

 in ruminants. Rumen digestion takes place at a pH of about 6.8. 



The use of wood for ruminants is not yet fully practical, although foliage, 

 wood, and bark of some species have some digestibility — hardwoods more than 

 softwoods (table 26- 14a). 



Millett et al. (1970) found that vibratory ball milling for 20 to 120 minutes 

 increased in vitro rumen digestibility of some woods. Aspen and sweetgum 

 showed maximum dry-matter digestibilities of about 75 percent, red oak 57 

 percent, and hickory 40 percent. Softwoods were less responsive to vibratory 

 bail milling than were the hardwoods. It is likely that in vivo digestibility would 

 be considerably less than these in vitro data suggest because such finely ground 

 material would pass quickly through the rumen. 



To chemically obtain, by treatment with alkali, acid, ammonia, or sulfur 

 dioxide, a product having the 60-percent in vitro digestibility of good-quality 

 hay, the lignin content of hardwoods must be reduced by 25 to 35 percent (Hajny 

 1981). 



Table 26- 14a. — In vitro digestibility of some woods and barks (Millett et al. 1970) 



Species 



Digestibility 



Trembling aspen . . . 



Soft maple 



Black ash 



Sugar maple 



White birch 



Yellow birch 



American elm 



Shagbark hickory . . 

 Eastern cottonwood 



White oak 



Red oak 



