Agriculture and Environment最新文献

The nylon bag technique has been used to study the effects of various reagents on the digestion of grass cell walls and straws in the sheep rumen. A large proportion of the acetyl groups were removed by sodium alkoxides in alcoholic solution with appreciable improvement in digestibility. Aqueous sodium hydroxide removed virtually all the acetyl, producing a correspondingly greater improvement.

When straw was treated with increasing amounts of sodium hydroxide, up to 10 g/ 100 g straw, the enhancement of digestibility was linear but not the release of acetyl; 2 g/100 g removed half the acetyl groups. After extraction with neutral detergent solution, followed by chlorite delignification, about 70% of the acetyl groups were left; sodium hydroxide treatment then had no effect upon the rate or extent of digestion of this residue.

Physical methods, based on X-ray diffraction and infrared absorption, showed that the degree of order of the cellulose component, which sets an upper limit to its rate of digestion, was not affected by concentrations of sodium hydroxide up to 20 g/100 g straw, more than sufficient to produce the maximum enhancement of digestibility.

Both electron micrography and chemical analysis indicated that the major components of the cell wall were removed simultaneously. It is concluded that the effects of basic reagents must be sought in the lignin-hemicellulose fraction of the cell wall, and that both covalent and hydrogen bonds may be responsible for its resistance to digestion.

Research aimed at improving the feeding value of maize stover for growing cattle is described. For various reasons, ensiling is considered preferable to dry harvesting. Sodium hydroxide treatments are discussed, and the rather disappointing in vivo results noted. Two wet processing systems are compared: ammoniation, and steam pressure treatment. An alternative is the grinding of dry harvested stover. Increased energy and fertiliser costs will make such treatments to utilise crop residues as feeds more economical.

In recent years much attention has been paid in Finland to the improvement of the feeding value of straw by ammonia.

In an 11-week trial milk cows were fed untreated barely straw, ammonia-treated straw or hay ad libitum, grass silage at 30 kg per day and barely meal and protein concentrate according to milk yield. The intakes of untreated straw, treated straw and hay were 1.1, 1.4 and 3.4 kg DM per day and milk yields (4%) 16.7, 16.4 and 17.7 kg per day, respectively. In the succeeding trial of 8 weeks the same feeds were used but the amount of silage was decreased to 20 kg per day. The intake of untreated straw DM was 3.5 kg, treated straw 3.1 kg and hay 5.9 kg per day. The milk yields (4%) were 21.6, 20.9 and 21.4 kg, respectively.

In a trial with growing cattle the diet included straw, barley meal and pr otein concentrate. The average daily intakes of untreated and treated barley straw from the age of 101 days to 381 days were 0.9 and 0.9 kg DM and live weight gains 1066 and 1092 g per day, respectively. In another trial from the age of 83 days to 363 days the animals consumed untreated barley straw 1.6 and treated straw 1.7 kg DM per day, and the live weight gains were 893 and 973 g per day, respectively.

The role of bacteria, protozoa and fungi in rumen digestion of plant cell wall material is briefly summarized. Literature evidence is presented suggesting a substantial contribution of entodiniomorph protozoa to fibre digestion in the rumen. Interactions between various bacteria degrading plant cell walls to volatile fatty acids, methane and CO₂ are described, as well as stoichiometry of fermentation. Net microbial growth yields in the rumen are discussed as net results of microbial synthesis and degradation (lysis). It is shown that the absence of protozoa lowers degradation and thus increases efficiency of synthesis. The effect of rumen defaunation on microbial protein supply to the animal is discussed. It is suggested that this effect is the result of: (1) a decrease in rumen fibre digestion; (2) an increase in efficiencies of microbial protein synthesis. Conversion of fibrous diets to soluble carbohydrates is suggested as a means of obtaining an optimal effect of defaunation on microbial protein supply to the animal.

As competition for food between man and livestock is increasing, the efficiency of animal production must be examined critically. Herbivores can use low quality roughages not edible by man and produce animal protein. Some conditions which affect the microbial digestion of poor quality diets and the yield of microbial protein, such asthe size of fermentation chambers relative to the size of the herbivore, availability of energy from feed, and the use of non-protein nitrogen, are discussed.

The effect of NaOH spray treatment on hay digestibility was studied by in vitro and in vivo methods. Four hay types were compared: untreated long or shredded hay and shredded hay treated with 3% and 6% NaOH. In vitro digestibility was measured by three methods: the Tilley and Terry procedure, a one-stage nylon bag technique (rumen digestibility only), and a two-stage nylon bag technique (rumen digestion + pepsin - HCl digestion). In vivo digestibility was estimated on eight young bulls given the four hay types at two levels according to a 2 x 2 latin square. In vitro and in vivodigestibilities of dry matter, organic matter and crude fiber were increased by the NaOH treatment. Both in vitro and in vivo techniques revealed the existence of an optimum NaOH concentration which in our experiments was close to the 3% treatment.

The loss of particulate dry matter and water-soluble dry matter from roughage has been studied in vitro with nylon bags with 5-, 6-, 10-, 20- and 36-μm apertures. Degradation of the acid detergent fibre (ADF) fraction and the disappearance of lignin were subsequently studied in situ using nylon bas with 5-, 6-, 10- and 20-μm apertures. There are only small and non-significant differences in the loss of particulate dry matter between nylon bags with 5-, 6- and 10-μm apertures. Increasing the aperture from 10 to 20 μm significantly (P < 0.0001) increases the loss of particulate dry matter. The amount of water-soluble dry matter is also substantially increased from nylon bags with 10- to those with 20-μm apertures. There are significant differences in the degradation rate of the ADF fraction between nylon bags with 5- and 10-μm apertures (P < 0.0001) and between nylon bags with 10- and 20-μm apertures (P < 0.0003). Mainly this is reflected in the digestion during the first 24 h. The loss of particulate dry matter in situ, measured as lignin loss, is quite similar for nylon bags with 5- and 10-μm apertures. Between nylon bags with 5- and 20-μm apertures on the other hand, the difference in lignin loss is highly significant (P < 0.0001). It is concluded that for samples milled to pass a 1-mm screen, a membrane aperture of 10 μm is a good compromise considering inflow and washout.

Baled straw was used as a control material (1). Other straw materials were pressed into cobs. These included: straw pressed without additives (2); NaOH-treated pressed straw (3); pressed compound cobs with the ingredients 50% NaOH-treated straw, 40%grain (oats + barley) and 10% beet molasses (4); and straw pressed with 10% molasses (5). Diets 1,2,3 and 5 were supplemented with soy—barley mixture (1:1) 400 g/day peranimal and diet 4 with soy 100 g/day per animal. A Na-free mineral mixtures was included in all and NaCl was given with 1,2 and 5. A digestibility trial was carried out with castrated adult male sheep using a latin square design. The digestibility of organic matter was higher in control straw (47) than in pressed straw (40) or straw to which molasses was added (43). NaOH-treated pressed straw was digested better (57) than control straw. Compound straw—grain pellets had the highest digestibility (67).

Approximately 250 samples of cereal straw were analysed for the digestibility of organic matter in vitro. From known relationships between digestibility in vitro and metabolism experiments in vivo, it was calculated that the digestibility in vivo of the straw samples ranged from 28 to 50%. For one and the same cultivar the range was 18 percentage units. The content of metabolizable energy in the straw samples ranged from 3.9 to 8.3 MJ per kg of organic matter.

Lignocellulosic wastes are a major underutilized resource. To convert them into useful feeds, processing in some form is usually required to enhance the rate and/or extent of digestion and to increase daily intake.

Mechanical processing, such as grinding and pelleting, usually increases daily intake but decreases digestibility of the dry matter. The response to mechanical processing are generally greater with low-than with high-quality forages and with smaller, younger animals than with larger, older ones. This is attributed to the greater degree of comminution necessary before the residue will pass from the reticulo-rumen of the smaller animals. However, improved protein status of animals fed mechanically processed wastes may contribute to the higher daily intakes because more dietary protein escapes rumen fermentation.

Chemical processing is necessary to produce useful feed from some highly-lignified wastes. NaOH and NH₃ have been the most extensively investigated chemicals and both are used commercially for improving the nutritive value of low-quality forages. NaOH treatment often shows a greater increase in digestibility when evaluated byin vitro procedures than when evaluated in vivo, particularly at higher levels (over 5%) added NaOH. This is probably due to physiological effects of the high level of Na, as diluting the treated material with other feed often improves the apparent digestibility. Variations in the composition of the starting material and in treatment conditions, especially with NH₃, can affect the results from chemical treatment. Adequate supplementation with protein, minerals and vitamins are required for optimum levels of production from animals fed chemically treated lignocellulosic wastes.

Considerable research is underway to find practical ways of using microbial processes to improve the nutritive value of lignocellulosic wastes. While several approaches are promising, none has yet reached widescale commercial application.

Most of the research on processing lignocellulosic wastes has been done with straws, stover and low-quality forages and to a lesser extent with forest industry wastes. Other wastes exist in all parts of the world which could be improved in nutritive value by processing. The development of practical procedures for treatment could greatly increase the world supply of food from animals.