Agriculture and Environment最新文献

Large populations of anaerobic fungi have been shown to colonize plant fragments in the rumen of cattle and sheep on fibrous diets. Plant material entering the rumen is rapidly colonized by flagellated zoospores that attach and produce hyphae that grow and penetrate deeply into the plant tissues. The growing fungus develops an extensive rhizoid for anchorage and supply of nutrients, and (later) a sporangium. Rupture of the sporangium and release of zoospores completes the developmental cycle. The fungi colonize mainly plant vascular tissues and highest numbers are found on stem fragments. The more fibrous the diet the greater the fungal population, and anaerobic fungi are absent from rumen contents of sheep grazing soft leafy plant materials. The major route of fungal invasion is via areas of damaged epidermis. The fungi can be grown in culture on a wide range of solid substrates. Cellulase activity has been demonstrated in anaerobic cultures containing strips of filter paper. Fungi similar to the rumen organisms have been shown to be present in the foregut and hindgut of a wide range of different types of herbivorous animals. The extent of colonization and growth on fibrous plant fragments suggests a significant role in cellulose digestion in the rumen. The ability of fungi to penetrate deeply into tissues not normally accessable to bacteria also suggest a special role for anaerobic fungi in rumen fibre digestion.

Recent work in the United States on the use of cellulose wastes for animal feed is reviewed. Most of the waste is produced in the central States; the densest centres of residue and beef cattle production do not coincide. The amount of residue that must be left in order to prevent soil erosion varies quite widely. Treatment of agricultural and other wastes (paper, wood, wood pulp) with alkalis and other agents to improve ruminant digestibility are reviewed.

Timothy grown in northern Sweden was harvested at varying maturity. Residues were prepared by extraction with ethanol or incubation in vitro, using rumen liquor or a commercial cellulase. The content of acetyl and phenolic (p-coumaric- and ferulic acid) substituents increased with maturity in all residues. Incubation with rumen liquor caused removal of a higher proportion of the substituents than the cellulase treatment. It was notable that ferulic acid was removed to a much greater extent than p-coumaric acid substituents. Acetyl and p-coumaric acid substituents, assumed to be linked mainly to the xylans, were proportionally less digestible in rumen liquor than xylose.

Studies have been conducted to compare the increases in dry matter digestibility (DMD) in vitro and in vivo and to determine the metabolisable energy (ME) value of straw ammoniated at ambient temperature. Stacks of straw sealed with polyethylene were allowed to react with 3% (w/w) of anhydrous NH₃ for 30 and 56 days respectively. Both DMD in vitro and total nitrogen (N) tests were carried out over an 8-week period subsequent to opening the stacks. Digestibility in vivo was measured with twelve wether lambs. Separate digestibility studies involving six wether lambs were conducted to measure N retention from ammoniated straw. There was a mean increases of 15 and 14.2 percentageunits in the DMD in vitro and in vivo content respectively of the ammoniated straw irrespective of whether it was treated for 30 or 56 days. The crude protein (CP) equivalent content of the straw was increased from 3.1 to 7.6%. The increase in DMD in vitro of the ammoniated and N content was maintained in all cases throughout the 8-week sampling period. Approximately 58% of the anhydrous NH₃ added to the straw appeared irreversibly “bound”

The N retention studies resulted in a slight increase in N retention as a result of straw ammoniation. The mean values for the control and ammoniated straw DM were—0.586 g N and—0.345 g N/100 g straw per day respectively. The ME values for ammoniated straw averaged 7.14 MJ/kg on a DM basis. Straw ammoniation resulted in a marked increase in intake with sheep.

Because man is monogastric, much of the world's plant production cannot be used by him directly as food. This applies not only to pasture and forest produce but also to a considerable part of the produce of arable land (bran, beet- and citrus pulp, oilseed residues, etc.). With the present methods of agriculture, maximal production of food for mankind can best be obtained by a combination of plant and animal husbandry, as will be shown. This is mainly due to the fact that ruminants (through their symbiosis with microbes) can utilize feeds rich in cullulose.

Even ruminants often have difficulty in utilizing such feeds, as their volume and slow digestion lower voluntary intake and as the nutritive value of the ingested feed per kg is often low. Some physiological data are presented which determine the rate of this digestion. Any treatment which would speed up and improve digestion would result in a higher productivity of these animals. Several methods are known for this purpose. To test their effectiveness, trials with animals have to be performed but analytical laboratory measurements are also useful. Such teniques were discussed at a recent EEC workshop at Lelystad, which is reported.

Research with pigs fed with higher contents of cellulose id presented and suggestions are made as to how these animals might benefit from treatments of these feeds.

Grape seed oil meal is the dried toasted residue after extraction of the oil from crushed grape seeds with hexane. This by-product of the wine industry contains about 11% crude protein and 52% crude fibre in the dry matter. The digestibility of the organic matter amounted to only 27% and could not be increased by treatment with 4% NaOH. Two series of beef production trials were carried out with a total of 196 young store bulls to study the feed value and the usefulness of this feedstuff.

A first series of beef production trials was carried out with 70 young bulls (4 groups) fed with complete dry rations based on 50% dried sugarbeet pulp. Grape seed oil meal (5 or 10% of the ration) was compared with linseed chaff (10%) or pollards (10%). No significant difference in average daily gain could be observed among the different treatments. Energy intake was very similar for the four experimental rations.

A second series of beef production trials was carried out with 126 young bulls fed with complete dry rations based on 70% dried sugarbeet pulp (control group). In the second and third experimental groups 5 or 10% sugarbeet pulp was substituted by 5 or 10% grape seed oil meal. In the fourth experimental ration, 10% sugarbeet pulp was substituted by 10% grape seed oil meal treated with 4% NaOH. Substituting 5 or 10% dried sugarbeet pulp by grape seed oil meal results in a very similar daily growth level, but feed conversion efficiency was lower. A lower feed and dry matter intake per kg gain was observed for the alkali-treated group (4th group: 10% grape seed oil meal + 4% NaOH) compared with the 3rd experimental group (10% grape seed oil meal).

The potentially indigestible plant cell wall components in representative samples of feedstuffs and animal feces (resp. a and b, expressed as a percentage of the neutral detergent residue, NDR) can be measured after incubation of these materials with mixed rumen microorganisms for several weeks at 40°C. From these values the percentage of NDR that was digested in the animal can be calculated. Similarly, the procedure can be used to estimate the digestibility of specific cell wall carbohydrates such as cellulose and hemicellulose after analysis of acid detergent fiber (ADF) and lignin.

The validity of this procedure was tested in digestion trials with ponies and wethers fed grass hay. The digestibility coefficients for NDR hemicellulose and cellulose determined with the in vitro procedure did not differ significantly from values obtanied with the conventional in vivo digestion trial.

The in vitro procedure has been applied to measure NDR digestibility in a variety of animals such as grazing geese and several species of exotic ruminants fed a mixed diet of hay and concentrates.

The resistances of low quality plant residues to anaerobic digestion are related to the high content of total structural matter and its intrinsic physicochemical characteristics. Natural factors include lignin, tannins and biogenic silica, while processing and storing further reduce quality through non-enzymatic browning reactions, and changes in particle size and physical surface properties. Delignified materials may exhibit greater lag and lower rates of digestion. Exchange capacity is much reduced in treated materials. Individually plant residues vary in the nature of their principal limiting factors. Silica is the primary factor in rice straw and lignin in most other crop residues. The effect of lignin depends on covalent linkage with structural carbohydrate and lignin obligately protects 1.4 times its own weight of carbohydrate in untreated materials. Lignin cleaved by alkali treatment is soluble in neutral detergent as evidence by ultraviolet absorption of neutral detergent extracts. It may lower digestibility of solubles through dilution and tanning reactions. The efficiency of alkali treatment of graminaceous straws can be assayed by the measurement of saponifiable groups within the residual structural matter.

Methods are reviewed for the determination of the constituents of the plant cell wall together with factors that are believed to affect its biodegradability; these factors include lignin and other phenolic constituents, silica, the crystallinity of cellulose and cell wall type. Attention is also given to the measurement of the biodegradability of the cell wall including its rate of degradation. The modification of cereal straws and other lignocellulosic wastes by various treatments is discussed in relation to the production of materials suitable as components of feeds for ruminants. The possible occurence of undesirable chemical reactions during processing is also considered.