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OCR for page 69
Forest Residues
INTRODUCTION
Wood residues such as wood pulp and bark have been used as energy
sources for ruminants during periods of critical feed shortages, but they
have never been generally recognized as alternatives for conventional
feedstuffs under normal economic conditions (Scott et al., 19691. Although
more than 1.5 million tons sulfate and sulfite pulps from spruce, pine,
and fir were fed to cattle and horses in the Scandinavian countries during
World War II when feed supplies were limited (Hvidsten and Homb,
1951; Nordfeldt, 1951), the feeding of wood pulp to livestock ceased
when conventional feedstuffs became available. Feeding of wood-derived
feedstuffs in North America has been largely experimental, with the ex-
ception of isolated situations in which wood residues have been fed on a
commercial scale.
WHOLE-TREE RESIDUE AND FRACTIONS OF WHOLE TREES
Quantity
Historically there has been little need for forest inventory information on
quantities of forest biomass beyond information on raw material needed
by the forest products industry. As a result, inventories estimated the
volume of forest biomass as merchantable boles of commercially important
tree species measured from a minimum of 13 cm diameter at breast height
69
OCR for page 70
70 UNDERUTILIZED RESOURCES AS ANIMAL FEEDSTUFFS
(DBH) to a minimum top diameter of 10 cm. There have been recent
attempts to estimate the total annual forest biomass available for use as
feed, fuel, and chemical raw material. Some of these estimates assume
current commercial forestland area and forest management practices while
other estimates assume maximum forest biomass production from fully
stocked, intensively managed forestland. A report by the Society of Amer-
ican Foresters (1979) indicates that the annual forest biomass production
from present commercial forestland area could double by the year 2035.
The estimates of annual forest biomass potential are shown in Table 7.
In addition, the report indicates that if 10 percent of the arable land that
is currently private forest, pasture, range, and hay land were used for
intensive production, up to 240 million dry tons additional annual forest
biomass production could be available. If the additional land were managed
under short-rotation, intensive-culture biomass farms, the increase could
be nearly 450 million dry tons annually (Inman, 19771.
Some studies have been made to measure and to develop methods to
estimate the weight of forest biomass for various species, based on DBH
TABLE 7 Estimates of U.S. Aboveground Forest Biomass Potential
(millions dry tons)
2035 to 2085
(With Full
2010 to 2035 Stocking and
(With Full Intensive
Source19701976a2002a Stocking) Management)b
Net growth from
commercial forest408481544 726 1,088
MortalityC1 091 091 09 1 09 1 09
Other sources100100100 100 100
Harvest for
conventional
product uses-17?- 181- 236 - 236 - 290
Total440509517 699 1,007
NOTE: Estimates are derived from data published by Zerbe (1977) and U.S. Department
of Agriculture (1977). Moderate industrial demand is projected (Society of American For-
esters, 1979).
aNet growth estimates from Thomas H. Ellis, USDA Forest Service, Oct. 20, 1978.
bModerate industrial demand is projected to the year 2020, and it is also assumed that
intensive management will double growth on 50 percent of commercial forest.
CAssumes mortality is recoverable. Intensified management may reduce mortality, but an
equivalent volume would be available as live wood.
Land clearing, noncommercial lands, urban tree removal, and urban wastes.
Reprinted courtesy of the Society of American Foresters.
OCR for page 71
Forest Residues 71
and height measurements or on DBH alone. Whole-tree weight tables for
23 species growing in New York have been published (Monteith, 19791.
The results are tabulated by species and DBH, showing fresh and dry
weights of the whole tree (aboveground portion), of the entire bole, and
of the bole cut off at various top diameters. Monteith also derived pre-
diction equations for green and dry weight of the various components for
10 species and made recommendations for application of these equations
to other species. Eleven species of puckerbrush ranging from 1.0 cm to
16.5 cm DBH were sampled and the total fresh and dry weights measured,
along with the fresh and dry weights of leaves, branches, and stems (Ribe,
19734. Prediction equations were also developed to calculate the fresh and
dry weight, the total, and each component for various DBH of each
species. Ek and Dawson (1976) have published the dry-weight yields of
Populus "tristis #1" grown under short-rotation intensive culture. The
results are expressed in terms of dry-weight yields at four spacings of
from 0.23 x 0.23 cm to 1.22 x 1.22 m at up to 5 years of growth. After
5 years they reported total aboveground weights at 1.22 x 1.22 m spacings
of 49.2 tons/hectare. This total weight yield consisted of 10.76 tons wood,
1.88 tons bark, 24.72 tons wood and bark, 6.32 tons twigs, 5.22 tons
leaves, and 0.35 tons other.
Since aspen (Populus tremuloides Michx., P. grandidentata Michx.,
and P. balsamifera L.) is the species that has most potential as a livestock
foodstuff, it should be considered separately. Aspen is the most widespread
species in North America. The range is controlled by adequate moisture
levels and cool summer temperatures and stretches from Mexico to the
Arctic Ocean and from Maine to Alaska. Residue from aspen utilization
is usually 100 percent because when aspen is commercially utilized, it is
often the only species processed. Commercially important concentrations
of aspen exist in the Northeastern, Great Lakes, and Central Rocky Moun-
tain areas of the United States, and the central portions of Canada. The
growing stocks in the Rocky Mountain and Lake States areas of the United
States are over 100 and 200 million m3, respectively (U.S. Department
of Agriculture, 1976~.
Collectibility
Not all of the annual forest biomass potential shown in Table 7 is collec-
tible. Some will be on lands where it is too costly to harvest because of
terrain or distance from markets. Some will not be harvested because of
environmental, aesthetic, wildlife, and soil fertility considerations. Har-
vesting as much as possible of the annual growth from forests under the
current forest management practices, and especially under intensive forest
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72 UNDERUTILIZED RESOURCES AS ANIMAL FEEDSTUFFS
management practices, requires new and innovative forest harvesting
equipment and schemes. Whole-tree harvesting equipment is currently
used to obtain pulp-chip-quality wood and a feed-quality by-product. This
equipment was developed during the early 1970s to harvest whole-tree
chips for the pulp and paper industry. Currently, the main emphasis is to
develop equipment to harvest forest biomass for fuel.
Although limited quantities of forest biomass will be available in the
future from primary and secondary wood processing plants, biomass avail-
ability for livestock feed will most likely be obtained directly from the
forest. This material could be a by-product of the system for the harvesting
of whole-tree pulp or fuel chips. The by-product would consist mainly of
the leaves or needles, twigs, buds, and wood and bark fines. If veneer,
pulp, and sawmill logs were harvested, the potential feedstuff would be
a by-product of harvesting the tree tops and branches, and it would also
contain leaves, needles, twigs, buds, and wood and bark fines. In the
case of short-rotation, intensively managed tree farms, the feedstuff could
consist of the whole tree, but most likely would be a by-product after
separation of stemwood, which would be used for pulp and fuel chips.
The collectibility of aspen depends upon the region of the country. In
the Lake States, northeastern areas of the United States, and central Can-
ada, aspen residues from primary wood processing plants are available,
as well as whole-tree or portions of whole-tree chips. In the Rocky Moun-
tain areas where less aspen is harvested, only modest amounts of residues
from primary processing are available. Whole-tree or portions of whole-
tree chips are not available in the Rocky Mountain area because this
harvesting method is not yet practiced there.
The primary markets for aspen in the Lake States, northeastern United
States, and central Canada are for pulpwood, sawlogs, and composition
board. Residue from these uses are bark, which contains up to 50 percent
wood, and sawdust that may contain some bark. These residues are col-
lected and, if not currently used, constitute a disposal problem. For a
large operation, such as a pulpmill, a sawmill with dry kilns, or a com-
position-board plant, the bark and other wood residues are usually burned
to supply process and space heat. This can require all of the residue wood
except in the case of a sawmill with dry kilns. A sawmill usually requires
only about one-half of the sawdust and bark to kiln-dry the lumber. The
remainder is often used for landfill or sold as cattle bedding, mulch, or
fuel. Where whole-tree harvesting is practiced for pulp chips, the segre-
gated fines and bark are put back on the soil. This residue accounts for
up to 20 percent of the harvest, and some of it may have value as a
feedstuff. If the whole tree is harvested for fuel without further processing,
the fines could be separated at the burning site for feedstuff use. If whole
OCR for page 73
Forest Residues 73
tree aspen is to be processed to fuel pellets (6 mm diameter x 15 mm
long), the fines would not be available because they are fuel for the drier;
but the fuel-pellet product could be suitable as a feedstuff.
In the Rocky Mountain area, considerable aspen is available. It is not
often harvested, however, because it is in scattered stands, usually at
elevations of between 2,100 and 3,300 m, and long distances from pro-
cessing plants and markets.
Physical Characteristics
Many forms of residues are produced from wood processing plants. For
instance, sawmill residue consists of sawdust, planer shavings, lumber
edge and end trim, slabs cut from the outer portions of the log, and
shredded bark. Usually the larger pieces are processed to pulp chips or
used for fuelwood or charcoal. The shredded bark, sawdust, and shavings
frequently have no markets, but these residues are used increasingly as
fuel by the forest products industry.
The particle size of sawdust, planer shavings, and shredded bark de-
pends upon the processing equipment used. Particle size of sawdust is
usually less than 6 mm. A sawmill cutting lumber from bark-free aspen
logs in the Lake States will produce sawdust with about 10 percent, by
weight, of the particles greater than 6 mm, about 40 percent between 6
mm and 10 mm, and 50 percent less than 10 mm. Planer shavings are
usually curls of wood 20 to 50 mm long and of various widths. The
particle size of shredded bark also depends upon the species and age of
the tree. Some barks are stringy, and older barks tend to break into small
pieces. Sometimes, especially in the spring, long strips of bark come free
of the log. Bark must be processed to achieve a smaller and more uniform
particle size for feeding. This can usually be done quite economically with
a hammermill.
Forest residues include treetops, branches, and short lengths of logs.
These residues can be reduced in size with portable chippers, such as
those used to make whole-tree chips. These chips would have to be further
reduced in size if they were to be used for livestock feed. The foliage can
be separated from wood and bark by air classification at the whole-tree
chipping site.
The bulk density of green sawdust is in the range of 250 to 350 kg/
m3. The moisture content of sawdust from a fresh log depends upon
species, time of year, and relative amounts of heartwood and sapwood.
Usually fresh or green sawdust will contain 40 to 50 percent water. The
bulk density of planer shavings can be as low as 100 kg/m3 for uncom-
pacted material and up to 250 kg/m3 for compacted shavings. The moisture
OCR for page 74
74 UNDERUTILIZED RESOURCES AS ANIMAL FEEDSTUFFS
content of planer shavings usually ranges from 7 to 15 percent because
the shavings are usually cut from dried lumber. The bulk density of
shredded bark is in the range of 250 to 350 kg/m3 if processed through
a hammermill. The moisture content of fresh bark is usually 40 to 50
percent. The bulk density of fresh whole-tree chips, uncompacted, ranges
from 300 to 400 kg/m3.
Storage of the residues and whole-tree materials is a problem when the
materials are fresh or have a moisture content above 17 percent. Numerous
studies have been made on the storage of fresh pulp chips and residue for
fuel use because of the decomposition and spontaneous combustion that
have occurred in large piles (Springer et al., ] 978; White, 19791. Among
the variables of storage are the geographic area, species, size of pile, time
of year, and particle sizes of materials in the pile. It would be advisable
not to store fresh materials intended for use as a livestock foodstuff. If
they are stored, it should be in piles less than 6 m high. If they are to be
stored in higher piles for more than a few weeks, provisions should be
made to monitor the temperature within the pile. The pile should not be
covered with plastic, canvas, or heavy snow because they trap heat and
cause more rapid internal heating in the pile. A low, uncovered pile will
ventilate and maintain low internal temperatures. Storing fresh wood in
anaerobic conditions such as a silo would be a suitable method to prevent
heating and decay organisms. Storing fresh bark, whole-tree chips, and
foliage is more difficult than storing wood in the form of sawdust, chips,
and shavings because of the higher amount of nutrients and biologically
active materials.
Nutritive Value
Most untreated woods are quite indigestible. Using an in vitro technique,
Millett et al. (1970) determined the relative digestibility of 27 species of
trees. A summary of the results is shown in Table 8. All of the hardwood
species examined showed some degree of digestibility, ranging from a
low of 2 percent to a high of 37 percent. Aspen was most digestible,
followed by soft maple and black ash. All of the softwoods were essentially
indigestible. These results are in general agreement with those Stranks
(1959) obtained with a pure culture of Ruminococcus flavefaciens. He
reported that aspen and ash were relatively digestible in vitro, whereas
elm, birch, and basswood required alkali or chlorite pretreatment before
they were appreciably digested. Nehring and Schramm (1951a,b) also
reported that ash, aspen, maple, and elm were superior roughage sources
for sheep, compared to oak and birch.
There is a positive correlation between the digestibility of the bark and
the wood of a given species, with the bark usually being more digestible
OCR for page 75
Forest Residues 75
(see Table 81. The rather high content of ether extract in some bark might
contribute to its higher digestibility.
As shown in Table 8, maple twigs and buds are more digestible than
the stemwood because they contain less lignin and have a higher percentage
of digestible protein and ether extract (Nehr~ng and Schutte, 1950~. The
soft maple buds and twigs had digestion coefficients of about 36 percent,
compared to 20 percent for the wood. It is well known that buds and twigs
are preferred brouse for a number of wild animal species.
TABLE 8 In Vitro Dry-Matter Digestibility of Various Woods and
Barks
Digestibility''
Substrate
Wood (%) Bark (%)
Hardwoods
Red alder
Trembling aspen 33 50
Trembling aspen (groundwood fiber) 37
Bigtooth aspen 31
Black ash 17 45
American basswood 5 25
Yellow birch 6 16
White birch ~
Eastern cottonwood 4
American elm 8 27
Sweetgum 2
Shagbark hickory 5
Soft maple 20
Soft maple buds 36
Soft maple small twigs 37
Sugar maple 7 14
Red oak 3
White oak 4
Softwoods
Douglas fir 5
Western hemlock 0
Western larch 3 7
Lodgepole pine 0
Ponderosa pine 4
Slash pine 0
Redwood 3
Sitka spruce 1
White spruce 0
a96-hour in vitro rumen digestibility. For comparison, the 96-hour digestibility of cotton
liners was 90 percent and of a reference alfalfa, 61 percent.
SOURCE: Millett et al. (1970). Courtesy of Journal of Animal Science.
OCR for page 76
76 UNDERUTILIZED RESOURCES AS ANIMAL FEEDSTUFFS
Table 9, taken from Millett et al. (1970), shows the water solubility of
various hardwood barks and the in vitro digestibility of the various barks.
Significant amounts of hydrolyzable oligosaccharides or phenolic glyco-
sides are present in the extracts of aspen and black ash barks. Approxi-
mately one-half of the total weight of material in a hardwood-bark water
extract of these barks appears to be carbohydrate that could be of nutritional
value to the ruminant. It is assumed the remaining portion of the material
consists primarily of phenolic compounds.
It is clear that there are large differences in digestibility between tree
species. Of the important tree species found in North America, aspen
(Populus spp.) is by far the most promising as a ruminant [eedstuff; thus
the emphasis below is on aspen.
Aspen Bark
Chemical Composition The chemical composition of aspen bark can be
quite variable. One of the more complete reports on chemical analysis
was prepared by Enzmann et al. (1969) (see Appendix Table 11. Crude
protein content of aspen bark is usually less than 3 percent on a dry basis.
From 5 to 10 percentile ether-extractable. Crude fiber is usually in the
range of 40 to 55 percent, and ash can be highly variable, depending upon
the amount of soil contamination.
Nutrient Utilization Enzmann et al. (1969) ground and ensiled aspen
bark containing 59 percent dry matter. Lambs were fed the ensiled bark
TABLE 9 Water Solubility of Various Hardwood Barks and Extent of
Carbohydrate Dissolution
Carbohydrates in
Water Extract
Weight Free Sugars After Dry-Matter
Loss Sugars Hydrolysis Digestibility
Species (%) (%) (%)a (%)b
Aspen 16.0 3.3 6.2 50
Black ash 22.1 6.5 10.0 45
Yellow birch 11.5 5.0 4.8 16
American elm 10.4 5.0 3.6 27
Sugar maple 5.5 1.7 1.9 14
al-hour hydrolysis at 121°C with 4 percent H2SO4 followed by neutralization with lime.
b96-hour in vitro rumen digestibility of unextracted bark.
SOURCE: Millett et al. (1970). Courtesy of Journal of Animal Science.
OCR for page 77
Forest Residues 77
in three forms: with no additions; as a mixture of 87 percent bark and 13
percent ground barley; and as a mixture of 87 percent bark, 13 percent
ground barley, and 0.025 percent Aspergillus oryzae fermentation product
on a wet basis. Digestible dry-matter content of the ensiled bark was 31.7
percent, and total digestible nutrient (TDN) content was 36.7 percent on
a dry basis. This compares with the TDN content of about 45 to 50 percent
for barley, rye, wheat, and oat straw. The mixtures of bark and barley
grain had a TDN content of 44 to 48 percent.
Mellenberger et al. (1971) offered goats diets containing 15, 30, 45,
or 60 percent of air-dried bark. By regression they determined that the
bark had a digestibility of about 50 percent. This experiment used smooth,
green bark from freshly cut trees. Bark from older trees may not be as
digestible. In a series of unpublished studies from this same laboratory,
aspen bark from other sources appeared to have a dry-matter digestibility
closer to 30 percent (L. D. Satter, University of Wisconsin, Madison,
1980, personal communcation).
Similar estimates of digestibility of aspen bark have been reported by
Gharib et al. (19751. This study was designed to test the effect of bark
particle size on digestibility. Lambs were provided diets that contained
20 percent ground corn, 20 percent soybean meal, and 60 percent bark,
plus a mineral and vitamin supplement. Dry-matter digestibility was 27.4,
25.7, and 30.3 percent for bark ground through hammermill screens of
0.32, 0.95, and 1.59 cm, respectively.
Animal Performance Relatively little information is available on animal
productivity when aspen bark is fed. Enzmann et al. (1969) offered diets
containing approximately 37, 53, or 68 percent ensiled aspen bark (dry
basis) to 40 kg wethers. The balance of the diet was a mixture of soybean
meal and oats. Wethers receiving diets containing 37 and 53 percent aspen
bark gained approximately 0.04 kg/day during the 48-day trial. Wethers
receiving the 68 percent bark diet lost about 0.04 kg/day. The authors
suggested that other feedstuffs, such as poor quality hay or straw, may
be better sources of energy during emergency periods than aspen bark.
Fritschel et al. (1976) fed ewes a diet containing approximately 67 to
70 percent aspen bark (dry-matter basis); 8 percent dehydrated alfalfa; 20
percent a mixture of ground shelled corn, oats, and soybean meal; and
the balance as mineral, salt, and vitamin mix. The ewes were on the
experimental diet for approximately 11 months, and during this time they
lambed, lactated, and were bred. The ewes readily consumed the feed and
had moderate gains in body weight. Consumption of the diet ranged from
about 1.7 kg to 3.0 kg/day, dry-matter basis. During lactation the ewes
received an additional 0.5 kg of a grain mix. An average of 1.3 lambs
were weaned per ewe. The ewes appeared normal in all respects, and their
OCR for page 78
78 UNDERUTILIZED RESOURCES AS ANIMAL FEEDSTUFFS
TABLE 10 Feedlot Performance of Cattle Fed Pelleted Diets
Containing Whole Aspen Tree Material (93 days)
48%
Alkali
12% 24% 36% 48% Treated
Performance Alfalfa Aspen Aspen Aspen Aspen Aspen
Initial weight
(kg) 321 32~) 318 318 319 319
Final weight
(kg) 375 405 425 431 422 422
Average daily
gain (kg/day) 0.6 0.9 1.2 1.2 1.1 1.1
Kg feed/kg gain 19.5 13.8 12.1 12.0 11.6 12.0
SOURCE: Singh and Kamstra (1981 a).
performance compared favorably with the control group, which was fed
hay.
Aspen Sawdust
Chemical Composition Aspen sawdust has a composition similar to that
of whole aspen tree. Protein content is less than 2 percent, and acid
detergent fiber is usually in excess of 60 percent. Ash content is usually
less than 1 percent, unless there is soil contamination, in which case ash
content may range up to 10 percent. Klason lignin content is usually
between 16 and 22 percent.
Nutrient Utilization The digestibility of aspen sawdust cut from bark-
free logs has been determined. Mellenberger et al. (1971) incorporated
sawdust into either high-roughage or high-concentrate diets at levels of
0, 20, or 40 percent, air-dry basis. As expected, the overall digestibility
of the high-roughage diets was lower than that of the high-concentrate
diets. Measures of apparent digestible dry matter decreased linearly with
both types of diets as the percentage of aspen sawdust increased from O
to 40 percent of the diet. Dry-matter digestibility of the sawdust portion
of the diet was 41 percent when it was incorporated into a high-roughage
diet and 28 percent in a high-concentrate diet.
Whole Aspen Tree
Chemical Composition As with other wood residues, crude protein con-
tent of whole-aspen-tree material is very low (see the section, "Forest
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Forest Residues 79
Foliages. Total ash and mineral content is normally low, but can be high
as a result of soil contamination (see Appendix Table 11.
Nutrient Utilization Little information is available on the digestibility of
whole-aspen-tree material. Digestibility studies of diets containing 0, 20,
40, or 60 percent of ensiled whole-aspen silage suggested that the diges-
tible dry-matter content of aspen silage in an 80 percent grain diet was
only 5 percent but approached 37 percent when incorporated into a 40
percent grain diet (Robertson et al., 1971~. This latter digestibility figure
is about 80 percent of that expected with wheat straw. Singh and Kamstra
( 1981 a) reported dry-matter digestibilities of 51, 52, 54, 60, and 63 percent
for total mixed diets containing 0, 12, 24, 36, or 48 percent ground whole
aspen tree.
Animal Performance A series of three experiments involving rather large
numbers of cattle fed whole-tree material have been reported from South
Dakota. In the first of these experiments (Singh and Kamstra, 1981a), 60
Hereford steers, each weighing approximately 320 kg, were allotted to
12 pens of 5 animals each. Mature aspen trees, including bark and leaves,
were harvested in summer in the Black Hills region of South Dakota. The
trees were chipped and dried to about 10 percent moisture. The dried
chips were hammermilled prior to incorporation into complete pelleted
diets. The six treatment diets were (1) 93 percent alfalfa (control), (2) 12
percent aspen, (3) 24 percent aspen, (4) 36 percent aspen, (5) 48 percent
aspen, and (G) 48 percent aspen treated with- 4 percent sodium hydroxide.
Soybean meal was incorporated into the pellets at a level equal to two-
thirds of the aspen present. A mixture of molasses and mineral and vitamin
mix constituted 7 percent of the pellet, with the balance of the pellet
supplied by alfalfa. A summary of animal performance in this trial is
shown in Table 10. The cattle fed aspen performed well, and actually
were more efficient in converting feed to body gain than were the cattle
fed alfalfa pellets. It should be pointed out that substantial amounts of
soybean meal were present in the aspen treatments, and that much of the
animal response may be due to the highly digestible soybean meal. The
authors concluded, however, that the aspen had a net energy for main-
tenance (NEm) of 1.53 Mcal/kg and net energy gain (NEg) of 0.48 Meal/
kg. These values are slightly higher than what one would expect from
medium-quality hay.
In the second study (Singh and Kamstra, 1981b) 60 Hereford steers,
each weighing 327 kg, were divided into six treatment groups and fed to
a slaughter weight of 500 kg. The six treatment groups received the
following diets: (1) a high-roughage control composed of 93 percent al
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110 UNDERUTILIZED RESOURCES AS ANIMAL FEEDSTUFFS
diet of 60 percent alfalfa and 40 percent concentrate was compared with
two diets containing 66 percent pulp fibers (a bleached hardwood kraft
and a bleached mixed species sulfite), 5 percent alfalfa, and 29 percent
concentrate. In the second, a diet of 70 percent barley and 30 percent
alfalfa was compared with those diets containing approximately 70 percent
of the bleached sulfite pulp and three different nitrogen sources. In all
cases the pulp-fed lambs had desirable carcass characteristics equivalent
to or higher than the controls. Based on growth measurements, the pulp
fiber was considered to have about 85 percent of the energy value of
barley.
Processing
Many pulp and paper residues are highly digestible, and it is not expected
that they will require processing. In the case of utilization of the fines
from a mechanical pulpmill where the fines are merely groundwood,
processing requirements are the same as for wood and sawdust of the
same species. If the materials are too contaminated with inorganics or
other papermaking additives, it is doubtful if further processing could be
justified on the basis of economic and animal health considerations.
Utilization Systems
Presently, fines from a sulfite pulpmill are being incorporated into live-
stock diets. The fines contain parenchyma cells, short fibers, and fiber
bundles obtained from a pulpmill making fiber for tissue from birch, beech,
and maple species. The process is an ammonia-base sulfite pulping pro-
cess. The experimental program started with the testing of fines from an
identical pulpmill operated by the same company that made pulp from
aspen. The testing consisted of chemical analysis of the fines for lignin,
carbohydrate content, ash, mineral elements, fats, and in vitro rumen
digestibility. In vivo digestibility was determined with goats, and addi-
tional feeding trials with sheep were made to determine palatability and
the effect of palatability on general health indicators (Millett et al., 19731.
The fines used are identified in Millett's report as aspen sulfite parenchyma
cell fines (unbleached). Additional feeding trials were made with beef
animals (Fritschel et al., 1976~. Nearly 50,000 kg were fed during a 3-
year cooperative study between the Forest Products Laboratory, University
of Wisconsin-Madison, and Procter and Gamble Company. Additional
feeding trials were conducted by the Agricultural Research Service (Dinius
and Bond, 19751. As a result of this and other research (Lemieux and
OCR for page 111
Forest Residues 111
Wilson, 1979), pulp fines containing about 65 percent water are presently
being fed to dairy cows and beef animals in Pennsylvania.
This experimental program required close cooperation between re-
searchers of various disciplines, pulpmill management personnel, and
corporate research staff. At the end, it involved close cooperation between
pulpmill management and county agricultural agents to explain to the
farmers how the fines are produced and how they should be used.
The use of additional spent sulfite pulp fines in animal diets requires
study to determine how to make the material available without causing
serious changes in the material and energy balances in the pulpmills and
how best to utilize it near its source.
Potential
The results of these studies involving pulpmill residues showed that the
cellulosic fiber fines from two pulpmills, each producing about 31 metric
tons (dry basis) per day, could be used in animal diets. The extension of
these results to other pulpmill residues could have a lasting and continued
impact on agricultural land use, food production, and wise use of our
renewable resources.
Sludges
Chemical Composition
In addition to the residues described above, pulpmills and papermills may
produce primary clarifier or lagoon sludges. Table 28 shows the com-
position and the in vitro dry-matter digestibility of various combined
pulpmill and papermill sludges (Millett et al., 19734. Most of the sludge-
containing by-products are very high in ash, and moderate to high in
lignin. Both of these characteristics diminish the feeding value of the
sludge. The Klason lignin values in Table 28 also include acid-insoluble
paper additives (ash) as lignin. Errors in the lignin analysis are evident
in the data listed in Table 21 for the combined pulpmill and papermill
residues that have high ash content.
Nutrient Utilization
Because the groundwood mill sludges are mostly groundwood, digesti-
bility is expected to be low, although the total carbohydrate content is
high. One of the semichemical pulpmill sludges was high in digestibility
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1 12 UNDERUTILIZED RESOURCES AS ANIMAL FEEDSTUFFS
TABLE 28 Composition and In Vitro Rumen Digestibility of
Combined Pulpmill and Papermill Sludges
Composition (dry-matter basis)
Total In Vitro
Klasona Carbohydrate Dry-Matter
Type of Residue Lignin (%) (%) Ash (%) Digestibility (%)
Groundwood mill
Mixed species plus
some mixed
chemical pulps 50 41 38 24
Southern pine plus
some hardwood
kraft 24 60 15 19
Semichemical
pulpmill
Aspen 20 71 2 57
Aspen plus mixed
hardwoods 55 29 13 6
Chemical pulpmill
De-inked
wastepaper,
tissue 23 71 22 72
Softwood sulfite,
glassine 13 74 14 66
Reprocessed milk
carton stock 28 67 25 65
Mixed chemical
pulps, tissue 17 76 13 60
Mixed hardwood
bleached kraft,
printing 17 75 11 59
Aspen sulfite,
tissue 19 77 2 50
Aspen and spruce
sulfite, tissue 45 46 45 35
Secondary waste
treatment sludge 38 5 45 5
aIncludes ash not soluble in H2SO4
SOURCE: Millett et al. (1973). Courtesy of Journal of Animal Science.
and total carbohydrate and low in ash, but the other was low in digestibility
and total carbohydrate. This indicates the amount of variation that can be
observed between products from mills that use the same pulping process.
Dinius and Bond (1975) fed a mixture of 65 percent pulp fines and 35
percent sludge. The activated sludge was the residue from processing total
pulpmill wastes through a lagoon system and constituted 30 percent of
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Forest Residues 113
the diet. At 38 percent protein, it provided the sole nitrogen source. The
remaining 5 percent of the diet consisted of inorganic salts. Organic-matter
digestibility of this diet was 78.9 percent, but animal acceptance of the
diet was poor. Dry-matter consumption was only 1.2 percent of body
weight.
Spent Sulfite Liquor
The chemical composition of spent sulfite liquor (SSL) varies greatly and
depends upon wood species, pulping reagent, reagent composition, and
pulping conditions. For a normal yield of calcium bisulfite-sulfurous acid
reagent pulp, the spent sulfite liquor can contain 12 to 16 percent total
solids, 30 percent of which consists of monosaccharides with some oli-
gosaccharides. The sugars in the presently unutilized spent sulfite liquor
can be concentrated and mixed with molasses. Klopfenstein et al. (1973)
reported that calcium and ammonia spent sulfite liquor can be effectively
used as a liquid feed ingredient in beef cattle diets, but that it contains
only about 50 percent as much energy as cane molasses per unit of dry
matter because of lignin residues.
WOOD RESIDUES AS ROUGHAGE SUBSTITUTES IN RUMINANT DIETS
Ruminants generally require a certain level of roughage in their diet.
Roughage provides tactile stimulation of the rumen wall and promotes
rumination, which in turn increases salivation and supply of buffer for
maintenance of rumen pH. Roughage in the dairy diet can help maintain
normal milk fat test, and in high-grain feedlot cattle diets can lower the
incidence of rumen parakeratosis and liver abscess. When traditional sources
of forage or roughage are expensive or in short supply, alternative rough-
age sources could be helpful. Wood residues have been investigated for
this purpose.
Aspen sawdust has been shown effective as a partial forage substitute
in a high-grain dairy diet (Salter et al., 19701. Cows fed 2.3 kg hay and
about 17 kg of a pelleted diet containing one-third aspen sawdust main-
tained normal milk fat. Cows receiving a similar diet but without sawdust
produced milk with 50 percent as much fat. Diets with one-third sawdust
are not practical, however, for high-producing dairy cows. A subsequent
study (Satter et al., 1973) was done in which lower levels of sawdust
were fed with high-grain diets, with or without sodium bicarbonate and
sodium bentonite. It was concluded that aspen sawdust can be a partial
roughage substitute in lactating dairy cow diets and can be helpful in
maintaining near-normal milk fat content in high concentrate diets. The
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114 UNDERUTILIZED RESOURCES AS ANIMAL FEEDSTUFFS
sawdust cannot serve as the only source of roughage for lactating cows
because of the irregular feed intake that results if no other forage is fed.
Oak sawdust is essentially indigestible, and has been used in several
growth or feedlot trials as a roughage substitute (Anthony and Cun-
ningham, 1968; Dinius et al., 1970; El-Sabban et al., 1971~. Inclusion of
5 to 15 percent oak sawdust in the diet has generally supported animal
performance equal to the other experimental groups being tested. Unfor-
tunately, the design of these experiments or the numbers of animals used
prevent firm conclusions regarding the value of oak sawdust as a direct
replacement for conventional roughage. The study of El-Sabban et al.
( 1971 ) does suggest that the incidence of liver abscesses did decrease with
increase in dietary sawdust up to 15 percent of the diet. Rumens of steers
fed diets containing sawdust were parakeratotic, but did show improve-
ment, particularly when coarse sawdust particles were fed. It has been
generally concluded that oak sawdust is an effective roughage substitute
when used as 5 to 15 percent of the total diet. Similar conclusions were
reached when pine sawdust was used as a roughage substitute in beef
finishing diets (Slyter and Kamstra, 1974~.
ANIMAL HEALTH
Generally, whole-tree or tree residues are not considered dangerous to the
health of livestock. It is essential, however, that diets containing wood
residues be properly balanced for all of the essential nutrients. Wood
residues must be considered primarily as energy sources. They contain
only small amounts, or are nearly devoid, of many essential nutrients.
Thus, animals consuming diets containing large amounts of wood residues
will encounter ill health if the diets are improperly balanced.
Pine needles have been shown to be toxic and can cause abortion in
cattle. Pregnant mice fed an extract of ponderosa pine (Pinus ponderosa)
needles had reduced litter size, and thus can serve as indicators of potential
toxicity problems (Cogswell and Kamstra, 19801.
Wood residues that have been exposed to chemical treatments, such as
in the pulping process, should be carefully examined for residual chem-
icals. In the pulp and papermaking industry, the process or method of
handling waste streams can unwittingly result in contamination of the
potential feedstuff. Sludges in particular need careful scrutiny. A number
of sludges have digestibility values comparable to hay. Their suitability
for animal feed, however, will depend on the amount of ash and the
chemical nature of the individual ash constituents. For example, moderate
levels of clay-type filler could be tolerated, but the presence of more than
trace amounts of certain heavy metals would rule out use as a feedstuff.
n
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Forest Residues 115
Thus, each pulp and papermaking residue should be chemically charac-
terized before it can be recommended as a feedstuff.
REGULATORY ASPECTS
The use of wood and wood-derived products in animal feeds requires the
consideration of and compliance with state and federal regulations.
The Association of American Feed (control Officials (1980) reported
that ground whole-tree aspen (Populus spp.) and/or its parts can be fed
to animals provided that the diets are supplemented with protein, vitamins,
and minerals.
RESEARCH NEEDS
The relatively low digestibility of most wood residues has stimulated
research into ways of treating or processing wood residues to increase
digestibility. A number of approaches have proven effective in increasing
digestibility, but they are costly and not economically feasible. The need
for a cost-effective process is clear. While the need is very great for such
a process, the likelihood of developing one may be diminished as cost of
energy and chemical inputs increase.
A major portion of the total wood residue is the residue that is left in
the forest at the time of harvest. This suggests that improved techniques
for whole-tree harvest be developed so the heretofore underutilized por-
tions of the tree may be available for collection, processing, and transport
to a site for utilization. In this connection, more research is needed on
the nutritive value of the foliage portion of trees used for pulpwood.
Commercial equipment exists for chipping whole trees, and sorting out
the wood chips from leaf, bark, and twig material at the point of harvest.
As this method of harvesting grows, so will the potential supply of foliage
material. Much more information is needed on the feeding value of the
foliage, and how feeding value is influenced by time of harvest, storage
of the foliage, and the genetic background of the tree (clone from which
the foliage was derived).
Most of the wood residues that have potential as feedstuffs are relatively
high in moisture. This causes problems in storage because of deterioration.
Research is needed to identify low cost means of preserving high moisture
wood residues. Preservation through ensiling and the use of mold inhibitors
are approaches that might be fruitful.
A significant portion of the research that has been done with wood
residues has involved sheep or goats. Unfortunately they are not as well
suited as cattle are to digest low-quality fibrous feeds. Sheep and goats
OCR for page 116
1 16 UNDERUTILIZED RESOURCES AS ANIMAL FEEDSTUFFS
are selective browsers, and normally select the more easily digested plant
material from their grazing environment. Cattle, because of their larger
size and capacity for retaining slowly digested materials in the rumen for
longer periods of time, can more easily accommodate the poorer-quality
feedstuffs (Van Soest, 19824. Future research with the relatively low qual-
ity wood residues should, wherever possible, utilize cattle rather than
sheep or goats.
SUMMARY
The carbohydrates of whole-wood residues are, with few exceptions, re-
sistant to attack by cellulolytic organisms in the rumen. This resistance
apparently stems from the close physical and chemical association between
cellulose and lignin, augmented by the crystalline nature of cellulose itself.
Whether or not the carbohydrates contained in wood lignocellulosic res-
idues can be utilized by rumen microbes will depend largely on how
extensively the lignin-carbohydrate complex can be altered or opened up.
Of the woods tested, all of the coniferous species are essentially un-
digested by rumen microorganisms. Deciduous species, with a few ex-
ceptions, are only slightly digested. Aspen is the most digestible species
tested, giving both an in vitro and in vivo digestibility of about 35 percent.
Aspen bark is about 50 percent digestible.
All of the chemical and physical pretreatments discussed are effective
to some extent, but exhibit a strong species preference that severely limits
their applicability. Hardwoods are generally more responsive to pretreat-
ment than softwoods, but even hardwoods exhibit a broad range of re-
sponsiveness. Aspen is particularly susceptible to treatment. Several of
the treatment methods, technically speaking, can be readily adapted to a
commercial process. The cost of treatment has presented the biggest bar-
rier. Conventional feedstuffs need to be relatively high priced before
treated wood residues can compete in the marketplace. Prices of conven-
tional feedstuffs have on occasion reached levels that would make treated
wood residues attractive. The lack of a steady market has discouraged
development of commercial wood processing enterprises.
Wood has been shown to be effective as a roughage replacement. De-
pending upon the other dietary ingredients, concentrations of 5 to 15
percent screened sawdust in diets for beef cattle appear practical. For
lactating dairy cows, aspen sawdust could be used as a roughage extender
or as a partial roughage substitute in high-grain diets. Some long hay
appears to be necessary in the diet to stabilize feed intake.
Finally, it must be realized that wood residues are generally low in
protein and other essential nutrients that livestock require. This necessitates
OCR for page 117
Forest Residues 117
more extensive supplementation. Treated wood residues are primarily an
energy source, and some may compare as an energy source to an average-
or low-quality hay. For this reason, treated residues are best suited for
ruminants having relatively low nutrient requirements, such as overwin-
tering beef cows and ewes and "dry" dairy cows, and for larger size
dairy and beef replacement heifers. Foliage does, however, contain sig-
nificant protein and other essential nutrients that could make foliage quite
useful as a feedstuff. If the foliage can be economically harvested and
stored, it may be a potential animal feedstuff.
Some of the many pulp and papermaking residues that are already
partially delignified but that have little fiber value for paper manufacture
have excellent potential as ruminant feedstuffs. Care must be used in their
selection as feedstuffs, however, because some residues may contain toxic
materials.
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Representative terms from entire chapter:
forest residues
