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The UK metabolisable protein system proposed an approach for calculating the energy (termed fermentable metabolisable energy) available for rumen microbial protein synthesis. This approach does not take into account rumen undegradable organic matter (OM; mainly protein and starch) and ignores the dynamic aspects of the value, such as rate of fermentation. The aim was to evaluate three techniques to estimate OM apparently degraded in the rumen (OMADR) of different forages.
The experiment was conducted using a range of forages with accurately predetermined OMD values (ADAS) to compare rumen liquor (RL) and faeces (FA) as sources of inocula in the pressure transducer technique (PTT) (Theodorou et al., 1994). Gas production results were examined in relation to OMD determined in vitro (PTT, Tilley and Terry) and in vivo.
The gas production (GP) technique has previously been used to estimate the gas volume (fermentable energy (FE)) of compound feed ingredients for ruminants (Newbold et al., 1996). It was shown that the FE content of feed mixtures was represented by the combination of the total gas from the incubation of the individual feeds. However this additivity might not be consistent throughout the incubation period. The objectives were to test whether 1. other GP parameters give better estimates of FE for simple mixtures and are they additive; 2. whether organic matter apparently degraded in the rumen (OMADR) explain differences in GP; and 3. to find out if there are any other better measures than OMADR for estimating FE.
During ensilage readily fermentable organic matter (OM) is fermented to lactic acid and short chain volatile fatty acids (VFA). These acids provide little energy as ATP for rumen microbial growth and are essentially absorbed intact. The UK metabolisable protein system defined the energy available for microbial growth, termed fermentable metabolisable energy (FME), as the proportion of metabolisable energy (ME) in a diet/feed less the ME in oil and fermentation acids. The aim was to establish if fermentation acids yield direct gas production resulting from microbial fermentation. Grass silage was simulated using grass hay (GH; containing no fermentation acids) with additions of individual fermentation acids in solution.
GH (~2 kg) was oven-dried overnight at 100°C, nulled (1 mm screen) and then sieved (25 μm screen). 0.5 g GH was weighed into 250 ml Duran bottles according to the treatments; 1) GH + anaerobic incubation mixture (AIM, 85/15 v/v anaerobic medium and strained rumen fluid) + ~5 ml distilled water; 2) GH + AIM + ~5 ml fermentation acid solution (100 mg DL-lactic acid (LA)/10 ml, 30 mg acetic acid (AA)/10 ml or 20 mg n-butyric acid (BA)/10 ml) (equivalent to 100, 30 and 20 mg/g GH dry matter (DM) for LA, AA and BA respectively); 3) anaerobic medium (85 ml) + 15 ml clarified rumen fluid + ~5 ml fermentation acid (as treatment (2)).
It is known that supplementing dairy cow diets with full-fat oilseeds can be used as a strategy to mitigate methane emissions, through their action on rumen fermentation. However, direct comparisons of the effect of different oil sources are very few, as are studies implementing supplementation levels that reflect what is commonly fed on commercial farms. The objective was to investigate the effect of feeding different forms of supplemental plant oils on both methane emissions and milk fatty acid (FA) profile. Four multiparous, Holstein-Friesian cows in mid-lactation were randomly allocated to one of four treatment diets in a 4×4 Latin square design with 28-day periods. Diets were fed as a total mixed ration with a 50 : 50 forage : concentrate ratio (dry matter (DM) basis) with the forage consisting of 75 : 25 maize silage : grass silage (DM). Dietary treatments were a control diet containing no supplemental fat, and three treatment diets containing extruded linseed (EL), calcium salts of palm and linseed oil (CPLO) or milled rapeseed (MR) formulated to provide each cow with an estimated 500 g additional oil/day (22 g oil/kg diet DM). Dry matter intake (DMI), milk yield, milk composition and methane production were measured at the end of each experimental period when cows were housed in respiration chambers for 4 days. There was no effect of treatment diet on DMI or milk protein or lactose concentration, but oilseed-based supplements increased milk yield compared with the control diet and milk fat concentration relative to control was reduced by 4 g/kg by supplemental EL. Feeding CPLO reduced methane production, and both linseed-based supplements decreased methane yield (by 1.8 l/kg DMI) and intensity (by 2.7 l/kg milk yield) compared with the control diet, but feeding MR had no effect on methane emission. All the fat supplements decreased milk total saturated fatty acid (SFA) concentration compared with the control, and SFA were replaced with mainly cis-9 18:1 but also trans FA (and in the case of EL and CPLO there were increases in polyunsaturated FA concentration). Supplementing dairy cow diets with these oilseed-based preparations affected milk FA profile and increased milk yield. However, only the linseed-based supplements reduced methane production, yield or intensity, whereas feeding MR had no effect.
Several published reports on the nutritive value of whole-crop wheat (WCW) have been based on estimations from laboratory techniques, some of which were developed for grass silage. However, there is little information on the accuracy of such estimations. Therefore the aim of this study was to evaluate the suitability of predicting the in vivo digestibility of WCW from various less animal-dependent techniques.
The in situ and in vitro techniques have been adopted to estimate the degradability of organic matter (OM) in the rumen on the basis that this provides an estimate of ATP for microbial protein synthesis. However this assumption may be incorrect since ATP production requires the fermentation of degraded carbohydrate and Beever (1993) has shown that some degraded hexose can be used synthetically without ATP production. In addition, degraded OM from protein is likely to produce less ATP than the same amount of degraded carbohydrate. The gas production (GP) technique measures end products of fermentation and may be a better guide to ATP production. On the assumption that the in situ and in vitro techniques provide satisfactory estimation of OM degradability, the work discussed here used the GP technique to estimate the effective unfermentable OM fraction of the degraded OM (EUFDOM) for a range of concentrate foods.
Menke et al. (1979), Beuvink et al. (1992) and Theodorou et al. (1994) developed techniques for measuring the time course of gas production of foods fermented in vitro with rumen fluid. These techniques require description of the fermentation profile with an appropriate mathematical model. Although several authors have used these techniques to study the ruminal fermentation of foods, little information is available on the suitability of the model chosen for describing the fermentation profile of the food under study. In this study, the models of Ørskov and McDonald (1979), France et al. (1993) and Beuvink and Kogut (1993) were fitted to the in vitro gas production profiles of 10 whole-crop wheat (WCW) forages (cv. Slepjner) to determine the model most suited to describing the data.
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.
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.
When a food is ingested by a ruminant animal, the carbohydrate fraction of the food is fermented by the rumen micro-organisms to produce gas (predominantly carbon dioxide and methane) as well as volatile fatty acids (VFA). The gas production technique simulates this fermentation process and provides an estimate of both the rate and extent of fermentation. Comparing the gas production (GP) profiles of foods enables a comparison to be made of the fermentative characteristics of different foods. However, the technique uses a bicarbonate-based medium system with the rumen liquor. This complicates the GP profile because of the production of ‘indirect’ gas resulting from the reaction between the VFA and the bicarbonate ions.
Beuvink and Spoelstra (1992) measured the volume of gas produced from buffered rumen fluid when known amounts of VFA were added and observed that 20·8 ml gas were released per mmol VFA. However, there is variation between laboratories in terms of the composition of the medium that is used. Even when the same medium is used, significant differences have been observed in the GP profile when different types of apparatus were employed (Rymer and Givens, 1997). Media are gassed with carbon dioxide before they are added to the gas production system and it is possible that the concentration of carbon dioxide dissolved in the medium varies between experiments. The objective of this experiment, therefore, was to determine whether the volume of indirect gas produced was affected by the composition of the medium, the addition of carbon dioxide, and the technique employed to measure gas production.
Fat content is one of the main factors affecting the degradability and fermentability characteristics of oil-rich foods estimated by means of the in situ, in vitro and gas production techniques. Filtered fat, considered degraded/fermented, is of limited value to the rumen microbes and may inhibit fermentation. Pre-extraction of oil may be one way to solve this problem. The rumen organic matter degradability (OMD) and fermentability (FOM) of concentrate foods were evaluated in this study with and without oil extraction.
Fermentable energy (FE) was defined in the latest United Kingdom metabolizable protein system as energy available for microbial protein growth and multiplication in the rumen (Agricultural and Food Research Council, 1992). In this system the FE value was calculated by subtracting the metabolizable energy (ME) of fat and ME of any fermentation products from the ME of the food. This estimation is indirect and largely based on whole tract digestion data, thus it can not take into account the influence of rumen outflow, fermentation and degradation rate and digesta retention time in the rumen. In addition, this approach does not take into account undegradable protein and /or starch. As a result, the precision of the FE values are questionable. Therefore a precise, accurate, rapid, cheap and direct technique to measure FE from food ingredients should be developed. Such a technique should consider the factors mentioned above. This work evaluated the ability of four techniques to estimate the FE value of concentrate foods for ruminants.
The effect of botanical diversity on supply of polyunsaturated fatty acids (PUFA) to ruminants in vitro, and the fatty acid (FA) composition of muscle in lambs was investigated. Six plant species, commonly grown as part of UK herbal ley mixtures (Trifolium pratense, Lotus corniculatus, Achillea millefolium, Centaurea nigra, Plantago lanceolata and Prunella vulgaris), were assessed for FA profile, and in vitro biohydrogenation of constituent PUFA, to estimate intestinal supply of PUFA available for absorption by ruminants. Modelling the in vitro data suggested that L. corniculatus and P. vulgaris had the greatest potential to increase 18:3n-3 supply to ruminants, having the highest amounts escaping in vitro biohydrogenation. Biodiverse pastures were established using the six selected species, under-sown in a perennial ryegrass-based sward. Lambs were grazed (~50 days) on biodiverse or control pastures and the effects on the FA composition of musculus longissimus thoracis (lean and subcutaneous fat) and musculus semimembranosus (lean) were determined. Biodiverse pasture increased 18:2n-6 and 18:3n-3 contents of m. semimembranosus (+14.8 and +7.2 mg/100 g tissue, respectively) and the subcutaneous fat of m. longissimus thoracis (+158 and +166 mg/100 g tissue, respectively) relative to feeding a perennial ryegrass pasture. However, there was no effect on total concentrations of saturated FA in the tissues studied. It was concluded that enhancing biodiversity had a positive impact on muscle FA profile reflected by increased levels of total PUFA.
While livestock sector is the back-bone of Ethiopian economy, production levels are low due to a variety of causes. It is characterized by low milk production, poor growth rates, extended calving or lambing intervals and a relatively late age at maturity. The major constrain for this is seasonality of feed quality and poor availability during the dry season, with nitrogen supply especially limiting. However legume forages such as cowpea offer the possibility to enhance dietary N levels and improve livestock production (Abule et al., 1995). With its quick growth, drought resistance and rapid ground cover cowpea has become an essential component of sustainable subsistence agriculture in marginal lands and drier regions of the tropics. This study was conducted to examine the ability of cowpea forages, offered as a supplement to low quality maize stover, to enhance intake and production performance in growing Ethiopian highland sheep.
Armenia is a typical highland country with an average altitude of 1800 m. More than half of its territory is occupied by natural pastures and hay producing areas which form an important source of feed material for animal husbandry. However, in recent years the country has been experiencing an acute shortage of feed materials and as a result the total number of livestock and animal derived products has drastically dropped. During the transition to a market economy the government has been unable to import additional forage materials, therefore there is a need to utilise local resources more rationally. Limited studies of the nutritive value of Armenia’s forage plants has been carried out. Moreover, in previous studies the fundamental criteria for measuring forage quality has been largely limited to an assessment of crude protein (CP), total ash (TA), crude fat (CF), nitrogen-free extractable substances (NFS) and crude cellulose (CC) contents. Only recently have studies been undertaken to assess gross energy (GE) and in-vitro digestible organic matter (OM) in the dry matter (DOMD) contents, and OM digestibility (OMD) and digestible energy (DE) value of OM. The objective of this work was to summarize the published studies on chemical composition and to discuss the results of recent measurements of energy value and in-vitro digestibility of native forages in Armenia in order to facilitate the selection and utilisation of high quality forages by farmers.
Herrero et al. (1996) found that NIRS was able to calibrate and cross-validate the static values of gas produced from the incubation of Kikuyu grass using manual in vitro gas production. However, the fermentation kinetic coefficients were not calibrated satisfactorily by NIRS. The aim of this study was to investigate the potential of NIRS as a means of predicting fermentation and the France et al. (1993) model parameters obtained from the automated in vitro gas production experiments for a range of concentrate feeds.
Thirty-eight milled (1 mm) samples representing three typical concentrate feed types were scanned over the infra-red region covering 1100 to 2300 nm using an NIRS systems 6500 spectrometer. Optical data recorded as log 1/Reflectance were transformed to their standard normal variates and detrended values (SNV-D).
The use of small ruminants, such as sheep, in metabolism studies is more convenient as handling problems are reduced and their maintenance costs are lower, in comparison with cattle. However in vivo digestibility estimates obtained at maintenance are known to differ between these two species. With the increased use of in vitro gas production techniques, to evaluate ruminant feedingstuffs, it is of great importance to identify whether the species from which the rumen fluid inoculum is obtained has a significant influence on the results obtained.
Rumen fluid samples were obtained from a non-lactating Holstein cow (C) and six wether sheep (S) offered the same diet (80 % tropical grass and 20 % dairy concentrate) and prepared so as to have similar dry matter (DM) contents and therefore potentially the microbial mass. Nine substrates (two tropical grasses 1-2, tropical alfalfa 3, barley straw 4, and five temperate grasses 5-9) were examined.
Considerable efforts have been made regarding the use of faecal material to provide a microbial inoculum for in vitro feed evaluation systems. However total gas production, rate of gas release and the extent of degradation of feeds incubated using faecal inoculum are lower than those incubated in a rumen fluid medium. It has been suggested that this is due to lower microbial activity, a consequence of the different microflora and reduced microbial numbers (e.g. Mauricio, 1999). Microbial populations are dynamic so, as their enzyme activity profiles change rapidly, little information is obtained from examining these. However, their hydrolytic activity as reflected by their ability to degrade specific substrates can be simply measured and provides a potential method with which to assess the quality of inocula with respect to their use in in vitro systems. The data presented here are from a larger study in which the differences between the hydrolytic activity of faecal material and rumen contents as influenced by the time of sampling were assessed in vitro.