Wood residues are made up of complex carbohydrates, the percentage of which varies depending on the type of tree used and their stage of growth. In general, wood residues mainly consist of cellulose (50%), hemicellulose (20-30%) and lignin (15-35%), in addition to small amounts of soluble sugars, fatty acids, alcohols and proteins, especially in the wood of certain trees such as pine and deciduous trees in their early stages of growth.
Various chemical, biochemical and physical treatments have been suggested to increase the digestibility of wood by animals. These treatments include:
- Hydrolysis with various acids to dissolve cellulose
- Alkaline and ammonia treatment to saponify ester bonds and promote swelling beyond the dimensions swollen by water to increase microbiological penetration into the structure of the cell wall
- Break lignin-cellulose chemical bonds with various chemicals to produce digestible cellulose
- Grinding to very small particle size to change the crystal structure of cellulose
- High energy electron irradiation to break chemical bonds of lignin and cellulose
Animal feeding experiments
In one study, sawdust from pine, oak, aspen and other tree species was included in 10% of the diet of beef steers, resulting in equivalent performance to diets containing an equal amount of coastal Bermuda grass. However, steers fed 15% sawdust had lower bodyweight gains and consumed slightly less food than coastal Bermuda grass-fed animals.
In another study, oak sawdust was fed 5% and 15% of the diet and compared to oyster shells and ground timothy hay as forage-based feedlot rations. . Performance data indicated that sawdust could be used successfully at levels up to 15% rpm without significantly affecting performance. Coarsely ground sawdust gave better results than finely ground sawdust.
Aspen sawdust for dairy cattle
For dairy cattle, it has been shown that aspen sawdust can replace 30% of conventional feed in dairy cows producing 20 kg of milk per day without reducing digestible dry matter intake or milk production. Cows consuming aspen sawdust also maintained normal milk fat levels. At certain stages of the life cycle of dairy cows, dilution of the ration with wood has made it possible to regulate energy intake and therefore to avoid untimely fattening. In one study, grain consumption was controlled by including up to 45% wood fiber with grain in the diet of dairy cows.
Wood residue for fattening lambs
Processed wood residues were also added to the diet of the fattening lambs at a rate of 60% with a resulting 7% increase in growth rates and a higher digestibility value of dry matter compared to lambs receiving hay only as fodder material. These results have been attributed to the increase in the net energy of wood after chemical or physical treatment, as well as the increased efficiency of the animal in converting this energy in the rumen to volatile fatty acids (VFAs) for a use by the animal in growth and other productive purposes after digestion.
Liquid wood residue
There are also liquid residues from the manufacture of wood, either by sulphurization to produce cellulose, or by steam pressure to produce wood panels. The resulting material, in this case called wood molasses, is mainly made up of around 65% soluble sugars, which is equivalent to the percentage of sugars found in other types of molasses such as cane, beet or molasses. citrus fruits, thus providing an important source of energy in animal feed (Table 1). Wood molasses was used in some experiments at 10% of the total feed lamb concentrates after mixing with urea. There were no significant differences in animal production when feeding wood molasses or other types of molasses, such as beet molasses (Table 2), without adverse effects on the health or metabolism of the animal.
Points to consider
- Although limited amounts of wood residue or sawdust can be used as a forage factor or as a diluent in ruminant feed, it is evident that most wood species fed without chemical or physical treatment are not satisfactory in terms of food. as major components of the ruminant diet. This has sparked increased interest in weathering wood through such treatments to make it more acceptable and digestible by ruminants.
- Wood residues that have been exposed to chemical treatments should be carefully screened for residual chemicals that adversely affect animal health and production.
- Dry wood residues contain only small amounts, or may be almost devoid of many essential nutrients. Thus, animals whose diets contain large amounts of wood can be unhealthy if the diet is not properly balanced.
- Most wood residues are relatively high in moisture, which poses storage problems due to their deterioration. Therefore, research is needed to identify inexpensive ways to preserve high moisture wood residue. Preservation by silage and the use of mold inhibitors are approaches that could be successful.