SUMMARY Four experiments involving the two-stage in vitro digestibility technique of Tilley & Terry (1963) were undertaken to investigate whether cow rumen liquor could be replaced with effluent or extract from feed residue containing micro-organisms derived from the long-term rumen simulation technique (Rusitec) of Czerkawski & Breckenridge (1977). In Expts 1 and 2, the dry matter digestibility (DMD) of hay was determined using either cow rumen liquor or Rusitec liquid effluent or extract from feed after 48 h of digestion in a Rusitec apparatus using various volumes of liquor and artificial saliva. Digestibilities determined with rumen liquor were c. 70% (c.v. 1·2%) while those determined with Rusitec effluent or extract were c. 62% (c.v. 1·8%). In treatments common to Expts 1 and 2, Rusitec effluent digestibilities were more repeatable than extract or rumen liquor digestibilities. In Expts 3 and 4, Rusitec effluent was compared with cow rumen liquor for determining DMD of seven forages with DMD ranging from 33 to 70%. For a given feed there was good agreement between experiments in DMD values determined with Rusitec effluent, and for ten paired values there was a high correlation (r 2 = 0·976) between DMD determined by the two methods. DMD determined using rumen liquor ( y ) was accurately predicted by Rusitec liquid effluent digestibility (x) from the equation y = 2·663 + 1·06477.x; R.S.D. 2·433. The results show that Rusitec liquid effluent can be used instead of rumen liquor as a source of micro-organisms for the two-stage in vitro digestibility method. Routine use of Rusitec would obviate the need for using fistulated animals.

Two experiments were conducted to examine the feasibility of substituting hay with chemically treated beech-sawdust in diets of ruminants. Experiment I was aimed at comparing alkali treatment with acid treatment under pressure as a method of improving the nutritive value of sawdust. Experiment 2 examined the effects of incorporating acid-treated beech-sawdust as a substitute for hay, with or without wheat bran, on fermentation characteristics using an artificial rumen (Rusitec).

Development and application of modem technology for upgrading straw in Europe during the 1970's has stimulated intense interest in developing countries. Since 1980, twenty four international workshops have been held in Africa and Asia to consider research and development on crop residues as feed, with emphasis on improving their intake and digestibility in ruminants by treatment with ammonia generated from urea and/or supplementation. Despite much research and development at universities and experiment stations, farmer-uptake of the findings has been minimal. Reasons for this are manifold, but include difficulties of transporting and storing crop residues, insufficient trials at farmer-level demonstrating obvious economic benefits from treatment and supplementation, inappropriate technology and near-absence of agricultural extension services. The annual dry matter production of 2.0 t crop residue per 500 kg livestock unit in developing countries is a vast resource which is currently underutilised. Future population pressure in developing countries will require greater utilisation of crop residues as animal feed; hopefully ways of applying the recent research findings will be found.

Trials were conducted to investigate the digestibility and voluntary intake of Guinea-‘A’ (Panicum maximum, Jacq - Ecotype ‘A’) silage by sheep. Two-week and 3-wk growth of Guinea-‘A’ grass was harvested and ensiled chopped or unchopped into polyethylene-lined 210-liter metal drums. Wethers averaging 22 kg initially were used, and feces were collected by means of light harness and canvas bag. Apparent digestibilities of dry matter (DM), crude protein (CP), neutral detergent fiber (NDF) and acid detergent fiber (ADF) were higher (P < .01) for the 2-wk than for the 3-wk growth silage. Chopping the grass before ensiling increased (P < .01) the apparent digestibility of DM, CP, NDF, ADF and hemicellulose by wethers, compared with unchopped forage. In the voluntary intake trial no differences were observed for DM intake by wethers due to growth stage of the grass. Chopping increased (P < .01) actual DM intake by 26%.

A series of experiments was conducted to evaluate the nutritive value of Azolla species (Azolla caroliniana) as a supplementaru source of dietary nitrogen for high fibre-based diets. Experiment 1 was aimed at estimating the solubility of nitrogen and degradability of Azolla protein in rumen fluid. Azolla appeared to be low in soluble nitrogen compared to wheat bran. Azolla protein also showed a low rumen degradability but the post-rumen solubility of the undergraded protein was inadequate to categorise it as an exceptionally useful rumen non-degradable protein source. The second and third experiments examined the effect of incorporating Azolla (with or without urea) as a supplementary source of nitrogen for straw-based diets on fermentation characteristics using an artificial rumen (Rusitec). Untreated straw and Azolla in the proportion of 13:2 (SA) gave the lowest digestibility while the highest digestibility was recorded with the diet containing urea-ammonia-treated straw supplemented with Azolla in the same ratio (TSA-1). The addition of 100 mg urea day−1 to the same dietary combination of straw and Azolla (SAU-1) raised the dry-matter digestibility and estimated microbial dry-matter production by 45% and 60%, respectively. A further increase in supplementary urea to 500 mg day−1 (SAU-2) had no effect on digestibility or the output of microbial matter. The estimated ATP yield was highest with TSA-1 diet and lowest with SA diet. The estimated efficiency of microbial synthesis expressed as the yield of microbial nitrogen/unit of dry matter digested was lowest for the diet SA and highest for the straw diet supplemented with 100 mg urea. The diets that contained wheat bran showed a relatively higher efficiency than the others.

The results of two fermentation experiments conducted with an artificial rumen (rumen simulation technique—Rusitec) are reported. The first experiment compared the fermentation characteristics of a medium quality hay with those of untreated or urea—ammonia treated rice straw. Urea-ammonia treatment increased the digestibility, Volatile Fatty Acid production and microbial dry matter output compared with untreated straw. While the dry matter disappearance continued almost at the same rate up to 72h with urea supplemented straw, it levelled off after 48 h in the case o f ammoniated straw. The second experiement examined the effects of level of feeding and different roughage: concentrate ratios on fermentation characteristics of urea-ammonia treated rice straw. The output of VFA increased with the increase in feed intake and the level of concentrate in the diet. This was also accompanied by a steady decline in the acetate: propionate ratio. The ratio of VFA production: methane production was slightly lower for the high straw diets compared with in vivo values reported for good quality hay. However, increasing the quality of the overall diet by increasing the proportion of concentrate tended to increase this ratio to accepted values .

Rice straw is unique relative to other cereal straws in being low in lignin and high in silica. Unlike other cereal straws taller varieties of rice straws tend to be leafy while the leaves are less digested than stems. This may contribute to higher straw value with rice yield. There is genetic variation in straw quality but has not been exploited and tends to be smaller than environmental variation. Effort in plant breeding has been to develop short varieties with higher grain yield. This development has reduced straw quantity but not nutritive value. The relationship between plant genetics and silica metabolism is virtually uninvestigated, although reviews from plant physiology indicate it is a major factor.Silica and lignin in that order are the primary limiting factors in rice straw quality. Silicon is a nutrient element which has been overlooked largely because of its assumed inertness, but also because of its geochemical abundance that so greatly exceeds its metabolic use by plants and animals. Silicon is involved in several major roles in rice: carbohydrate synthesis, grain yield, phenolic synthesis and plant cell wall protection. These vectors interact with each other to eliminate statistical association of silica and lignin with straw digestibility when varieties are compared. Yield of grain is highly related to silica content of straw, which reflects soil availability. There are no detailed studies on rice straw lignin. Most papers reporting lignin contents in rice straw have used acid-detergent lignin by either the sulfuric acid or permanganate versions. There are undoubtedly soluble phenolics in rice straw that need investigation. The effects of ammonia and urea on silica is to crack the silicified cuticular layer. Silica is not dissolved by these reagents in contrast to the action of sodium hydroxide.Treatments on rice straw follow those applied to other lignified materials. In order of frequency of reports, urea followed by ammonia with comparatively fewer papers on sodium hydroxide, steam and pressure treatments or exploded by pressure release, and only one or two papers on acid treatments and white rot fungi. There are reports on animal supplementation and a few growth studies with young animals. Field surveys in India and the southeast Asian countries only report the use of urea, although it appears less efficient than ammonia. Farmer acceptance is related to their perceptions on costs, labor, equipment, health, safety, i.e. the exposure to ammonia vapor, economic and other social factors. The various papers reporting treatments have used animal digestion trials; a variety of in sacco, in vitro digestions with rumen organisms or cellulase, some in combination with pepsin digestion or neutral-detergent extraction. Gas production from in vitro rumen fermentation has also been used. Results are expressed mainly on dry matter basis and fewer reports on organic matter. Results are difficult to compare and standardization of procedures is badly needed. However, most treatments with ammonia and urea show some increase in digestibility and intake where measured in in vivo trials. In vitro and in sacco evaluations tend to overestimate improvement in digestibility.

Three trials were conducted in Sri Lanka to study the effects of growth stage, chopping length and additives on ensiling characteristics of Guinea-'A' (Panicum maximum, Jacq-Ecotype 'A') and NB-21 (Pennisetum purpureum, Schumac × Pennisetum americanum, L.). In the first trial, the grasses were harvested 1, 2 and 3 wk after clipping, chopped and ensiled in small laboratory silos (3-liter cardboard cylinders, double-lined with polyethylene bags) alone or with addition of either cassava (Manihot esculenta, Crantz), tuber meal (5%, wet basis), coconut (Cocos nucifera, L.) oil meal (5%, wet basis) or formic acid (3%, dry basis). Guinea-'A' grass contained an average of 2.3% N and 70.6% neutral detergent fiber (NDF); NB-21 contained 3.8% N and 65.9% NDF. Acetic acid concentration of silage was lowest when grasses were harvested after 1 wk of growth. Addition of cassava tuber meal or coconut oil meal decreased pH (P<.05) and increased lactic acid concentration (P<.05) of the silages. Generally, the effects were greater for cassava tuber meal. Addition of formic acid had no substantial effect on ensiling characteristics, compared with the control. In a second trial, Guinea-'A' grass was harvested 3 wk after clipping, chopped in three lengths (1.5, 7.5 and 15 cm), and ensiled in small silos. Lactic and acetic acid concentrations of silages increased (P<.01), whereas dry matter loss and pH decreased (P<.05) with fineness of chop. In a third trial, 2- and 3-wk growth of Guinea-'A' were harvested and ensiled in 210-liter metal drums, double-lined with polyethylene, chopped (1.5 cm) or unchopped. Cutting grass at 2 wk decreased (P<.01) pH and increased (P<.01) lactic acid concentration, compared with cutting at 3 wk. Dry matter loss was lower (P<.01) for chopped silage. Chopping decreased (P<.05) pH and increased (P<.05) lactic acid concentration of silage.

An experiment was carried out with sixty cross bred draught bull calves of 163 kg average liveweight to investigate the effect of six different methods of urea-ammonia treatment on the subsequent utilization of rice straw. Straw treated with 4% urea solution for 3, 9 and 27 days in closed pits and 3 or 9 days in open heaps was compared with untreated straw supplemented with 8·5% ground soyabean. Both 3-day treatments involved 8·5% ground soyabean added at the time of treatment as an external source of urease.

Three experiments were conducted with hammer-milled (10-mm screen) rice and barley straw treated with urea solution, alone or with urease enzyme.

Thirty-six Friesian cows in mid-lactation were used to compare the effects of nine treatments.

Spent tea leaf (STL) and seven other protein feeds were subjected to microbial fermentation in nylon bags in the rumen of two fistulated buffalo calves and subsequent acid-pepsin digestion in vitro.

Three experiments were conducted to evaluate the effectiveness of urea as a source of ammonia in an ‘ensiling’ process for improving the nutritive value of chopped rice straw.

SUMMARY1. Four experiments have been carried out to determine the effect of treatment of spring-sown barley straw (var. Deba Abed) with sodium hydroxide (NaOH) solution and subsequent neutralization with hydrochloric acid (HCl) on its digestibility and intake by sheep.2. In Experiment 1, chopped straw was mixed with 4·5 or 9·0 g NaOH in 200 or 800 ml water/100 g, straw, and after 24 hr neutralized with HCl and left for a further 24 hr before being offered to castrated male sheep (wethers) in a maintenance diet containing 35% concentrates. Organic-matter digestibility of straw significantly increased, by 8 and 11 percentage units respectively, after treatment with 200 ml solution containing 4·5 and 9·0 g NaOH. Volume of solution did not affect digestibility.3. In Experiment 2, straw treated as in Experiment 1 was given ad libitum. The highest intake was for straw treated with 200 ml solution containing 4·5 g NaOH/100 g straw, treatment with 9·0 g NaOH giving a significantly lower intake but higher than that of untreated straw.4. In Experiment 3, the in vitro digestibility of milled straw, treated as in Experiments 1 and 4, increased with increasing volumes of solution up to 120 ml/100 g straw, but the response to successive increments of NaOH declined progressively.5. In Experiment 4 chopped straw was mixed with 4·5, 6·75 or 9·0 g NaOH in 30, 60 or 120 ml water/100 g straw and offered as in Experiment 1. Treatments significantly increased straw digestibility, by 8 to 16 percentage units. Increasing the volume of water from 30 to 60 ml significantly improved digestibility, by 5 percentage units at the two lower levels of NaOH. The response to an increase in the level of NaOH was less, and inconsistent. In vitro and in vivo digestibilities were significantly correlated, but it is concluded that the in vitro technique used overestimates the digestibility of treated straw.