Energy, fuels, and chemicals 



3229 



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



— Continued 



Digestibility 



Species Wood Bark 



— Percent— 



SOFTWOODS 



Douglas-fir 5 



Western hemlock 



Western larch 3 



Lodgepole pine 



Ponderosa pine 4 



Slash pine 



Redwood 3 



Sitka spruce 1 



White spruce 



W. Jelks developed a process in which small amounts of nitric acid are 

 introduced, with a catalyst, to oak sawdust which is then steamed at 6 to 8 

 atmospheres pressure to produce a cattle food with about 50 percent digestibil- 

 ity. A sawmiller in Frohna, Missouri, who operates a feed lot with 600 to 700 

 cattle feeds a ration in which half the weight is this cooked oak sawdust. He 

 believes that his total feed costs are lessened because his requirement for corn 

 and soybean feed is significantly reduced.'^ At $3.00/bushel, com costs about 

 $125 per ovendry ton. 



It is also possible to increase disgestibility of some woods by a process 

 involving neither ball milling nor chemical addition. Bender and Heaney (1973) 

 found that briefly treating chipped wood with steam at 300 psi, and then termi- 

 nating the reaction by very rapidly discharging the chips to atmospheric pressure 

 increased digestibility of some wood — particularly aspen. In 1981, Stake Tech- 

 nology Ltd. was operating at least two cattle feeding operations in the United 

 States, one using steam treated aspen fiber, the other sugar bagasse, for a 

 significant proportion of the cattle's ration. Southern hardwoods such as oaks 

 are less well suited to the process than aspen. Readers needing a further review 

 of wood and wood-based residues in animal feeds will find Baker et al. (1975) 

 useful. 



CONTROLLED ENZYMATIC HYDROLYSIS 



Interest in controlled enzymatic hydrolysis of cellulose to glucose has been 

 spurred by the United States Army Natick Development Center's development 

 of strains of Trichoderma viride fungi and its mutants now designated as Tricho- 

 derma reesei. These fungi produce cellulase enzymes that have been tested on 

 several cellulosic substrates (Mandels 1979; Mandels et al. 1978; Bliss and 

 Blake 1977). 



The enzymatic hydrolysis process requires two stages. In the first, the 

 enzyme is produced by growing the fungus in a culture medium of cellulose 



' Personal communication in November 1981 with B. Lorenz, Frohna, Missouri. 



