The moisture content of samples affects the accuracy of predictions made using near infrared reflectance spectroscopy (NIRS). One way to prevent the problem is to develop a repeatability file, which summarizes variation in the spectra of a single sample resulting from variation in conditions at the time of scanning (Murray, 1993). Another method is to re-read the spectra of all samples on a second occasion when their moisture content has been deliberately altered (Murray, 1993). The present study, using straws with known voluntary intakes, compares these methods with a simple technique that compensates the spectra for moisture content before NIRS calibration (or prediction) begins.

In the semi-arid parts of west Asia and north Africa, barley straw (Hordeum vulgareL. subsp. vulgare)and cereal stubbles provide between one-quarter and one-half of the metabolizable energy (ME) offered to sheep. In barley straw, voluntary straw dry-matter (DM) intake (VSI) is a good predictor of body weight gain (R2 = 0.85; data of Capper et al., 1989). This varies according to location and year (CV = 0.30 to 0.40) and varies genetically, with an average genotypic CV of 0.07, which can exceed 0.10 in wet years. Genotype X environment interactions in VSI are important (Table 1).

A genetically high VSI is advantageous in cool, wet, favourable growing conditions, when VSI is normally low. In drought conditions, VSI is high, genetically varies relatively little (Table 1) and is less important for the farmer than straw and grain yields. Barley breeders working in drought-prone environments prefer to do most of their selection for yield in dry conditions (Ceccarelli, 1993). Breeders are increasingly selecting for high VSI but wish to focus their testing plots in dry areas. Therefore they need indirect tests that indicate the nutritive value of straw when it is grown in wet environments.

In vitro techniques have been developed to facilitate the measurement of nutritional variability amongst food. Many kinetic studies have utilized the modified Tilley and Terry technique, with long-term incubations carried out in Erlenmeyer flasks. These are inefficient in utilizing incubator space for large scale studies. However substitution of Erlenmeyer flasks with tubes as fermentation units leaves the system prone to ‘bridging’, the formation of dense mats of forage particles by entrapped gas, above the level of the media in a fermentation unit. The objective of experiment 1 was to establish an effective incubation technique to eliminate the random variation caused by bridging.

At maintenance at least, the whole tract digestibility of several foods in sheep and cattle is similar, consequently much of the information on the nutritive value of dairy cow foods in food composition tables is derived from studies conducted in sheep. However, Adesogan (1996) reported that in whole-crop wheat (WCW), starch digestibility is higher in sheep than in dairy cows. This study examined the validity of using sheep to model the ruminal degradation of WCW in cows by comparing the degradability of dry matter (DM) and nitrogen (N) of urea-treated WCW in both species.

Winter wheat (cv. Hussar) was harvested at 540 g DM per kg and conserved following urea application at target rates of 20 or 40g/kg DM (WCW2 and WCW4 respectively). The degradability of the forages was examined in dairy cows given 6 kg dairy concentrate and grass silage ad libitum and in wethers given 2.4 kg/day of grass silage supplemented with 0.36kg/day of rolled, mineralized barley.

In vitro systems to estimate foods nutrient quality at the rumen level are becoming increasingly attractive. From an economic aspect these systems provide considerable savings in terms of the number of animals, quantity of foods and labour input required, as well as the time taken to conduct a study. Equally important, from an ethical standpoint they have the potential of substantially reducing the number of surgically modified animals required. In addition, as the systems are, to varying degrees, artificial they tend to be highly repeatable and therefore ideally suited to routine analysis. With consideration to the above, the ANKOM in vitro fermentation system (Fairport, NY 14450, USA) was examined to determine its potential as an alternative to in situ rumen degradability studies. The results reported here are from part of that work.

The fractional rate of digestion as compared with the rate of passage can determine the extent of digestion in the digestive tract and the amount of potentially digestible matter escaping digestion (Van Soest, 1982). The lower the rate of digestion or the higher the rate of passage, the more nutrients escape digestion. The effect of rate of passage is higher for food components with slow rates of digestion such as neutral-detergent fibre (NDF) (Mertens, 1985). Increasing feeding level is associated with higher rate of passage, lower residence time in the rumen and decreased digestibility of nutrients. Digestibility depression is considered in several energy evaluation systems (van Es et al., 1978; Moe, 1981; Agricultural and Food Research Council, 1993 etc.) although most of the systems use a standard percentage discounting energy value, regardless of foods or nutrient components. Studies (Tyrell and Moe, 1975) showed that digestibility depression is higher for cell wall than cell solubles, whilst El Khidir and Thomsen (1983) reported that digestibility depression of cell walls was responsible for proportionately 0-7 of the observed decrease in digestibility. Mertens (1985) reported that energy discount factors can be related to NDF content and total digestible nitrogen value of foods. Ørskov (1996) recommended prediction of food potential of both energy value and intake from degradation characteristics.

Sugar cane bagasse is produced in large quantities in Brazil. The cultivated area of sugar cane in recent years has been around 4.2 X 106 ha/year, with a production of about 270 X 106 t/year of cane. As each tonne of cane produces around 300 kg of bagasse by-product, a large quantity of bagasse is generated.

Bagasse is of low dry matter (DM) digestibility (about 250 g/kg), because of lignification. Efforts have been made to improve the digestibility of bagasse using treatment with chemicals (sodium hydroxide, ammonia) or steam (Abdalla et al., 1990). Although steam and pressure treatments have improved in situ degradability, intake and digestibility in cattle were disappointing (Mello et al, 1989). Recently treatment of bagasse with irradiation and ammonia have been investigated.

As animal nutritionists are generally very cautious about using chemical analysis only for defining nutritional needs for livestock and as in vivo experiments are long, costly and subject to animal welfare legislation, much emphasis is placed on various in vitro analyses which are often regarded as being very informative in the absence of in vivo data. In vitro analyses may be applied to dry- (DMD) and organic-matter (OMD) digestibility and crude protein (CP) degradability (DG) and may involve ‘live’ cultures such as rumen fluid or gastric juices or ‘dead’ extracts containing enzymes. As part of an EU-funded Concerted Action (see Acknowledgements), a survey of the methods adopted for in vitro determinations (in vitro OMD, in vitro DG) for ruminants, pigs and poultry is underway: this paper presents a progress report of the information received to date concerning ruminant methods.

The participants in the Concerted Action were asked to provide details of the in vitro methods actually in use in their countries, with particular attention to the methods used by the so-called Feed Information Centres (i.e. Feed Evaluation Units) for routine analyses (i.e. not experimental work). The participants supplied details of modifications and/or references to methods and this information was collated and circulated for checking and comment.

Sorghum is a multipurpose crop where all parts of the plant are used for human food, animal food, fuel and fabrication. In comparison to other cereal crops it requires little water and it is tolerant to poor soils and adverse climatic conditions. It is one of the most widely grown crops in India particularly in semi-arid and rain-fed regions where the potential for crop and livestock production is limited by the availability of water. During the kharif season (July to October), it occupies about 10 million ha of land and produces a large quantity of stover which is given to farm livestock. The rabi season crop (November to February) occupies about 6 million ha of land and is mainly dependent upon residual moisture in the soil and provides both grain and forage. The economic value of sorghum stover as fodder sometimes exceeds that of the grain because seasonal shortage of food is an acute problem during the dry season. Much effort has been expended on improving sorghum varieties (Burton, 1973; Gupta et al., 1976; Dongi and Paroda, 1978), mostly directed towards increasing the yield. Pederson et al. (1982) compared the quality and agronomic traits of 49 forage sorghum hybrids and suggested that the most rapid way to improve the quality of forage sorghum would be to improve its in vitro dry-matter (DM) digestibility. There are several new strains of sorghum which have been improved in terms of agronomic characters but there is little information on the nutritional quality of their stovers. Therefore the objective of this study was to evaluate the stovers of several new sorghum strains in terms of chemical composition, in sacco DM disappearance (DMD) and their silage quality.

It is widely accepted that robust and accurate in vitro techniques are required to predict the proportion of food nitrogen (N) degraded in the rumen. One such technique is to estimate the solubility of food N. In these experiments, relationships between solvent soluble N and in situ rumen degradability of forage N were investigated.

Samples of 11 fresh grasses (FG) (mainly perennial ryegrass) and their corresponding silages (GS) were used. GS was prepared from material ensiled in laboratory scale silos for 90 days. Prior to the experiments, FG and GS samples were initially hand chopped to approximately 1 cm lengths. In the in situ study a fresh sample equivalent to 0-5 g DM was weighed into polyester bags (pore size 43 μ 200 X 90 mm internal diameter). Duplicate bags for each of FG or GS were incubated in the rumen of three wethers for 0, 3, 8, 16, 24, 45 and 72 h. The incubated residues including the 0 h samples were washed in a washing machine and freeze-dried for 48 h. Rumen degradability characteristics and effective degradability (ED, at rumen outflow rate of 0.08 per h) of N were calculated using the exponential model of Ørskov and McDonald (1979). In vitro solubility of N (S) was determined by incubating for 1 h (at room temperature) the fresh sample (0.5 g on dry matter basis) in each of the four solvents: Borate phosphate buffer (BFB), Durand's buffer (DB), clarified rumen fluid (CRF) and distilled water within a balanced three way factorial design (three operators; four solvents; 11 forages; Deaville et al., 1997). Residues from S were filtered under vacuum and the filter paper plus residue were oven dried for 18 h at 100°C. All samples and residues were analysed for total N using Kjeldahl method (Ministry of Agriculture, Fisheries and Food, 1986). Factorial analysis on the general linear model (Minitab®, 1994) was used in the analysis of variance(ANOVA) for in vitro data and regression analyses of in situ and in vitro data were performed (Minitab®, 1994). Only the regression results are reported here.

Fibrous foods are major sources of energy and protein for equids. The potentially energy yielding fraction of dietary fibre consists of non-starch polysaccharides (NSP). NSP cannot be digested by equine enzymes and in order for the animal to obtain energy from NSP it must be fermented by the gut microflora to yield volatile fatty acid. This fermentation process is less efficient in terms of yield of ATP than the digestion of starch to glucose, and is generally believed to occur solely in the large intestine. Plant protein may be associated with the NSP or the protoplast. However, horses can only utilize that protein which has been digested and absorbed in the small intestine. Thus, knowledge of the site and extent of nutrient degradation is important to enable the accurate formulation of diets for horses. Therefore in the current study the site and extent of NSP and crude protein (CP) degradation from four fibrous foods commonly given to horses in the United Kingdom were determined in caecally fistulated ponies using mobile bags.

The trial was a 4 X 3 incomplete Latin square design with three caecally fistulated Welsh X pony geldings (ca. 250 kg live weight) and four botanically diverse sources of dietary fibre. The ponies were maintained on a basal diet of hay and grass nuts and water was available ad libitum. Bags (6X1 cm) of monofilament polyester mesh pore size 4 μm were filled with 350 mg of either unmolassed sugar-beet pulp (SB), hay cubes (HC), soya hulls (SH) or oat hulls : naked oats (2:1) (OH: NO), which had been ground to pass a 1-mm steel mesh. On two consecutive mornings 20 bags were introduced into the ponies via a naso-gastric tube. Each bag contained two 100 mg steel washers which enabled their capture by a magnet placed inside the caecal fistula: the cannulae were positioned just posterior to the ileo-caecal junction. Between 10 and 16 bags were recovered on the magnet, the remaining bags were allowed to continue through the hind-gut and were subsequently collected in the faeces.