Comparison of energy evaluation systems and a mechanistic model for milk production by dairy cattle offered fresh grass-based diets

Grass-based diets are of increasing social-economic importance in dairy cattle farming, but their low supply of glucogenic nutrients may limit the production of milk. Current evaluation systems that assess the energy supply and requirements are based on metabolisable energy (ME) or net energy (NE). These systems do not consider the characteristics of the energy delivering nutrients. In contrast, mechanistic models take into account the site of digestion, the type of nutrient absorbed and the type of nutrient required for production of milk constituents, and may therefore give a better prediction of supply and requirement of nutrients. The objective of the present study is to compare the ability of three energy evaluation systems, viz. the Dutch NE system, the agricultural and food research council (AFRC) ME system, and the feed into milk (FIM) ME system, and of a mechanistic model based on Dijkstra et al. [Simulation of digestion in cattle fed sugar cane: prediction of nutrient supply for milk production with locally available supplements. J. Agric. Sci., Cambridge 127, 247-60] and Mills et al. [A mechanistic model of whole-tract digestion and methanogenesis in the lactating dairy cow: model development, evaluation and application. J. Anim. Sci. 79, 1584-97] to predict the feed value of grass-based diets for milk production. The dataset for evaluation consists of 41 treatments of grass-based diets (at least 0.75 g ryegrass/g diet on DM basis). For each model, the predicted energy or nutrient supply, based on observed intake, was compared with predicted requirement based on observed performance. Assessment of the error of energy or nutrient supply relative to requirement is made by calculation of mean square prediction error (MSPE) and by concordance correlation coefficient (CCC). All energy evaluation systems predicted energy requirement to be lower (6-11%) than energy supply. The root MSPE (expressed as a proportion of the supply) was lowest for the mechanistic model (0.061), followed by the Dutch NE system (0.082), FIM ME system (0.097) and AFRCME system(0.118). For the energy evaluation systems, the error due to overall bias of prediction dominated the MSPE, whereas for the mechanistic model, proportionally 0.76 of MSPE was due to random variation. CCC analysis confirmed the higher accuracy and precision of the mechanistic model compared with energy evaluation systems. The error of prediction was positively related to grass protein content for the Dutch NE system, and was also positively related to grass DMI level for all models. In conclusion, current energy evaluation systems overestimate energy supply relative to energy requirement on grass-based diets for dairy cattle. The mechanistic model predicted glucogenic nutrients to limit performance of dairy cattle on grass-based diets, and proved to be more accurate and precise than the energy systems. The mechanistic model could be improved by allowing glucose maintenance and utilization requirements parameters to be variable. (C) 2007 Elsevier B.V. All rights reserved.

Effect of variety, nitrogen fertiliser and various agronomic factors on the nutritive value of husked and naked oats grain

The effect of variety, agronomic and environmental factors on the chemical composition and energy value for ruminants and non-ruminants of husked and naked oats grain was studied. Winter oats were grown as experimental plots in each of 2 years on three sites in England. At each site two conventional husked oat cultivars (Gerald and Image) and two naked cultivars (Kynon and Pendragon) were grown. At each site, crops were sown on two dates and all crops were grown with the application of either zero or optimum fertiliser nitrogen. Variety and factors contained within the site + year effect had the greatest influence on the chemical composition and nutritive value of oats, followed by nitrogen ferfiliser treatment. For example, compared with zero nitrogen, the optimum nitrogen fertiliser treatment resulted in a consistent and significant (P < 0.001) increase in crude protein for all varieties at all sites from an average of 95 to 118 g kg(-1) DM, increased the potassium concentration in all varieties from an average of 4.9 to 5.1 g kg(-1) DM (P < 0.01) and reduced total lipid by a small but significant (P < 0.001) amount. Optimum nitrogen increased (P < 0.001) the NDF concentration in the two husked varieties and in the naked variety Pendragon. Naked cultivars were lower in fibre, had considerably higher energy, total lipid, linoleic acid, protein, starch and essential amino acids than the husked cultivars. Thus nutritionists need to be selective in their choice of naked or husked oat depending on the intended dietary use. (C) 2004 Elsevier B.V. All rights reserved.

Whole crop cereals 1. Effect of method of harvest and preservation on chemical composition, apparent digestibility and energy value

A total of 133 samples (53 fermented unprocessed, 19 fermented processed. 62 urea-treated processed) of whole crop wheat (WCW) and 16 samples (five fermented unprocessed, six fermented processed, five urea-treated processed) of whole crop barley (WCB) were collected from commercial farms over two consecutive years (2003/2004 and 2004/2005). Disruption of the maize grains to increase starch availability was achieved at the point of harvest by processors fitted to the forage harvesters. All samples were subjected to laboratory analysis whilst 50 of the samples (24 front Year 1, 26 front Year 2 all WCW except four WCB in Year 2) were subjected to in vivo digestibility and energy value measurements using mature wether sheep. Urea-treated WCW had higher (P<0.05) pH, and dry matter (DM) and crude protein contents and lower concentrations of fermentation products than fermented WCW. Starch was generally lower in fermented, unprocessed WCW and no effect of crop maturity at harvest (as indicated by DM content) on starch concentrations was seen. Urea-treated WCW had higher (P<0.05) in vivo digestible organic matter contents in the DM (DOMD) in Year 1 although this was not recorded in Year 2. There was a close relationship between the digestibility values of organic matter and gross energy thus aiding the use of DOMD to predict metabolisable energy (ME) content. A wide range of ME values was observed (WCW. 8.7-11.8 MJ/kg DM; WCB 7.9-11.2 MJ/kg DM) with the overall ME/DOMD ratio (ME = 0.0156 DOMD) in line With Studies in other forages. There was no evidence that a separate ME/DOMD relationship was needed for WCB which is helpful for practical application. This ratio and other parameters were affected by year of harvest (P<0.05) highlighting the influence of environmental and Other undefined factors. The variability in the composition and nutritive value of WCW and WCB highlights the need for reliable and accurate evaluation methods to be available to assess the Value of these forages before they are included in diets for dairy cows. (C) 2008 Elsevier B.V. All rights reserved.

Near infrared reflectance spectroscopy (NIRS) to predict biological parameters of maize silage: effects of particle comminution, oven drying temperature and the presence of residual moisture

Maize silage nutritive quality is routinely determined by near infrared reflectance spectroscopy (NIRS). However, little is known about the impact of sample preparation on the accuracy of the calibration to predict biological traits. A sample population of 48 maize silages representing a wide range of physiological maturities was used in a study to determine the impact of different sample preparation procedures (i.e., drying regimes; the presence or absence of residual moisture; the degree of particle comminution) on resultant NIR prediction statistics. All silages were scanned using a total of 12 combinations of sample pre-treatments. Each sample preparation combination was subjected to three multivariate regression techniques to give a total of 36 predictions per biological trait. Increased sample preparations procedure, relative to scanning the unprocessed whole plant (WP) material, always resulted in a numerical minimisation of model statistics. However, the ability of each of the treatments to significantly minimise the model statistics differed. Particle comminution was the most important factor, oven-drying regime was intermediate, and residual moisture presence was the least important. Models to predict various biological parameters of maize silage will be improved if material is subjected to a high degree of particle comminution (i.e., having been passed through a 1 mm screen) and developed on plant material previously dried at 60 degrees C. The extra effort in terms of time and cost required to remove sample residual moisture cannot be justified. (c) 2005 Elsevier B.V. All rights reserved.

Chemical composition and in vitro fermentation of tannin-rich tree fruits

Dry and mature tree fruits are a potential source of protein for goats in the semi-arid areas of southern Africa, but their chemical composition and feeding value is largely unknown. This study presents the chemical composition and in vitro fermentation of indehiscent whole fruits and separated seed and hull fractions from Acacia nilotica, Acacia erubescens, Acacia sieberiana, Acacia erioloba, Piliostigma thonningii and Dichrostachys cinerea trees. Results indicate that the N contents of whole fruits ranged between 13.5 g/kg DM (A. nilotica) and 27.1 g/kg DM (A. erubescens). Seeds had a higher N content than hulls for all tree species. A. nilotica, D. cinerea and P thonningii fruits had high levels of extractable phenolics (758, 458 and 299 g/kg DM, respectively). Soluble phenolics (SPh) and ytterbium precipitable phenolics (YbPh) levels were negatively correlated to in vitro gas production but positively correlated to in vitro organic matter degradability (iOMD). Partition factors for whole fruits at 48 h ranged between 3.6 mg/ml for A. erioloba and 7.8 mg/ml for A. nilotica. Seeds of A. erioloba, A. erubescens and P thonningii were consistently fermented more efficiently throughout the incubation period compared to their whole fruits or hulls. Estimating in vitro degradability of phenolic-rich substrates through filtration procedures can give erroneous results due to the loss of soluble phenolics, which are not necessarily degradable. The feeding value of fruits from D. cinerea and A. nilotica tree species may be reduced due to the presence of high levels of phenolics. (C) 2007 Elsevier B.V. All rights reserved.

In vitro microbial inoculum: A review of its function and properties

This review considers microbial inocula used in in vitro systems from the perspective of their ability to degrade or ferment a particular substrate, rather than the microbial species that it contains. By necessity, this required an examination of bacterial, protozoal and fungal populations of the rumen and hindgut with respect to factors influencing their activity. The potential to manipulate these populations through diet or sampling time are examined, as is inoculum preparation and level. The main alternatives to fresh rumen fluid (i.e., caecal digesta or faeces) are discussed with respect to end-point degradabilities and fermentation dynamics. Although the potential to use rumen contents obtained from donor animals at slaughter offers possibilities, the requirement to store it and its subsequent loss of activity are limitations. Statistical modelling of data, although still requiring a deal of developmental work, may offer an alternative approach. Finally, with respect to the range of in vitro methodologies and equipment employed, it is suggested that a degree of uniformity could be obtained through generation of a set of guidelines relating to the host animal, sampling technique and inoculum preparation. It was considered unlikely that any particular system would be accepted as the 'standard' procedure. However, before any protocol can be adopted, additional data are required (e.g., a method to assess inoculum 'quality' with respect to its fermentative and/or degradative activity), preparation/inoculation techniques need to be refined and a methodology to store inocula without loss of efficacy developed. (c) 2005 Elsevier B.V. All rights reserved.

A review and simplification of the in vitro incubation medium

The requirement to rapidly and efficiently evaluate ruminant feedstuffs places increased emphasis on in vitro systems. However, despite the developmental work undertaken and widespread application of such techniques, little attention has been paid to the incubation medium. Considerable research using in vitro systems is conducted in resource-poor developing countries that often have difficulties associated with technical expertise, sourcing chemicals and/or funding to cover analytical and equipment costs. Such limitations have, to date, restricted vital feed evaluation programmes in these regions. This paper examines the function and relevance of the buffer, nutrient, and reducing solution components within current in vitro media, with the aim of identifying where simplification can be achieved. The review, supported by experimental work, identified no requirement to change the carbonate or phosphate salts, which comprise the main buffer components. The inclusion of microminerals provided few additional nutrients over that already supplied by the rumen fluid and substrate, and so may be omitted. Nitrogen associated with the inoculum was insufficient to support degradation and a level of 25 mg N/g substrate is recommended. A sulphur inclusion level of 4-5 mg S/g substrate is proposed, with S levels lowered through omission of sodium sulphide and replacement of magnesium sulphate with magnesium chloride. It was confirmed that a highly reduced medium was not required, provided that anaerobic conditions were rapidly established. This allows sodium sulphide, part of the reducing solution, to be omitted. Further, as gassing with CO2 directly influences the quantity of gas released, it is recommended that minimum CO, levels be used and that gas flow and duration, together with the volume of medium treated, are detailed in experimental procedures. It is considered that these simplifications will improve safety and reduce costs and problems associated with sourcing components, while maintaining analytical precision. (c) 2005 Elsevier B.V. All rights reserved.

Production and metabolic effects of site of starch digestion in lactating dairy cattle

Milk solids yield in modern dairy cows has increased linearly over the last 50 years, stressing the need for maximal dietary energy intake to allow genetic potential for milk energy yield to be realized with minimal negative effects on health and reproduction. Feeding supplemental starch is a common approach for increasing the energy density of the ration and supplying carbon for meeting the substantial glucose requirement of the higher yielding cow. In this regard, it is a long held belief that feeding starch in forms that increase digestion in the small intestine and glucose absorption will benefit the cow in terms of energetic efficiency and production response, but data supporting this dogma are equivocal. This review will consider the impact of supplemental starch and site of starch digestion on metabolic and production responses of lactating dairy cows, including effects on feed intake, milk yield and composition, nutrient partitioning, the capacity of the small intestine for starch digestion, and nutrient absorption and metabolism by the splanchnic tissues (the portal-drained viscera and liver). Whilst there appears to be considerable capacity for starch digestion and glucose absorption in the lactating dairy cow, numerous strategic studies implementing postruminal starch or glucose infusions have observed increases in milk yield, but decreased milk fat concentration such that there is little effect on milk energy yield, even in early lactation. Measurements of energy balance confirm that the majority of the supplemental energy arising from postruminal starch digestion is used with high efficiency to support body adipose and protein retention, even in early lactation. These responses may be mediated by changes in insulin status, and be beneficial to the cow in terms of reproductive success and well-being. However, shifting starch digestion from the rumen impacts the nitrogen economy of the cow as well by shifting the microbial protein gained from starch digestion from potentially absorbable protein to endogenous faecal loss.

Effects of forage source and soybean and marine algal oil supplementation on milk fatty acid composition in ewes

The objective of the present studies was to determine effects of basal dietary forage source on the response of milk fatty acid composition to an oil supplement based (2:1, respectively, w/w) on soybean oil and marine algae biomass oil high in cis-9, cis-12 C18:2n − 3 and C22:6n − 3, respectively. In Study 1, Hampshire × Dorset ewes (48) were randomly assigned to one of four treatments and 12 pens in a completely randomized design blocked on the basis of lambing date and number of lambs suckled. Control rations (60:40 forage:concentrate, dry matter (DM) basis) based on alfalfa pellets (AP) or corn silage (CS) were fed from lambing. Beginning at 22 days postpartum, three pens of ewes fed AP and three pens of ewes fed CS were supplemented with oil (30 g/kg of ration DM) in place of corn meal. Average ewe DM intake (DMI) and average daily gain (ADG) were measured weekly. Milk yield and composition were measured at 42 days postpartum. DMI was lower (P<0.02) for CS and for oil, but milk yield was not affected by forage source or oil supplementation. Milk fat content was higher for oil (P<0.10) and milk protein content was higher for AP (P<0.04). Total CLA concentration (g/100 g fatty acids) increased (P<0.01) with CS and oil, and the response to oil was greater for AP (P<0.04). Similarly, total trans-C18:1 and C22:6ω−3 concentrations were higher for CS and oil, but the response to oil was greater for CS (P<0.06 and P<0.01, respectively). In Study 2, the experiment was repeated using alfalfa haylage (AH) instead of AP. The DMI decreased (P<0.05) with oil feeding, but was not affected by forage source. Milk yield was decreased by feeding oil with AH, but not by feeding oil with CS (P<0.03). Milk fat content tended to be increased by feeding oil with AH, but tended to be decreased by feeding oil with CS (P<0.08). Total CLA concentration was increased (P<0.01) for AH versus CS and by oil, and the response to oil supplementation was greater for AH (P<0.01). In contrast, total trans-C18:1 concentration was higher for CS versus AH, with a greater response to oil for CS (P<0.05). Feeding marine oil increased the C22:6ω−3 (P<0.01) concentration, and the response was greater for AH (P<0.04). To further characterize the response of milk fat composition to dietary oil in ewes, a third study used six pens of three ewes each assigned to either the control CS diet used for Study 2 or the same diet supplemented with 45 g/kg (DM basis) of the oil mixture. Feeding oil had no effect on DMI, milk yield or milk fat concentration, but again increased (P<0.001) total trans-C18:1 and C22:6ω−3 concentrations and numerically increased (114%) total CLA concentration. Milk fatty acid composition responses to supplemental vegetable and marine oils were affected by forage source. Milk trans-C18:1 concentration was higher when CS was fed in Studies 1 and 2, but the effect of forage species on CLA concentration differed between studies, which may reflect differences in diet PUFA content and consumption, as well as amounts of dietary starch and fiber consumed. Despite large increases in trans-C18:1 concentration, milk fat content was not decreased by feeding unsaturated oils to ewes, even at diet levels of 45 g/kg of ration DM.

Evaluation of NRC, UC Davis and ADAS approaches to estimate the metabolizable energy values of feeds at maintenance energy intake from equations utilizing chemical assays and in vitro determinations

Feed samples received by commercial analytical laboratories are often undefined or mixed varieties of forages, originate from various agronomic or geographical areas of the world, are mixtures (e.g., total mixed rations) and are often described incompletely or not at all. Six unified single equation approaches to predict the metabolizable energy (ME) value of feeds determined in sheep fed at maintenance ME intake were evaluated utilizing 78 individual feeds representing 17 different forages, grains, protein meals and by-product feedstuffs. The predictive approaches evaluated were two each from National Research Council [National Research Council (NRC), Nutrient Requirements of Dairy Cattle, seventh revised ed. National Academy Press, Washington, DC, USA, 2001], University of California at Davis (UC Davis) and ADAS (Stratford, UK). Slopes and intercepts for the two ADAS approaches that utilized in vitro digestibility of organic matter and either measured gross energy (GE), or a prediction of GE from component assays, and one UC Davis approach, based upon in vitro gas production and some component assays, differed from both unity and zero, respectively, while this was not the case for the two NRC and one UC Davis approach. However, within these latter three approaches, the goodness of fit (r(2)) increased from the NRC approach utilizing lignin (0.61) to the NRC approach utilizing 48 h in vitro digestion of neutral detergent fibre (NDF:0.72) and to the UC Davis approach utilizing a 30 h in vitro digestion of NDF (0.84). The reason for the difference between the precision of the NRC procedures was the failure of assayed lignin values to accurately predict 48 h in vitro digestion of NDF. However, differences among the six predictive approaches in the number of supporting assays, and their costs, as well as that the NRC approach is actually three related equations requiring categorical description of feeds (making them unsuitable for mixed feeds) while the ADAS and UC Davis approaches are single equations, suggests that the procedure of choice will vary dependent Upon local conditions, specific objectives and the feedstuffs to be evaluated. In contrast to the evaluation of the procedures among feedstuffs, no procedure was able to consistently discriminate the ME values of individual feeds within feedstuffs determined in vivo, suggesting that the quest for an accurate and precise ME predictive approach among and within feeds, may remain to be identified. (C) 2004 Elsevier B.V. All rights reserved.

The effect of wilting and soaking Eupatorium adenophorum on its digestibility in vitro and voluntary intake by goats

An experiment was conducted to determine what effect simple treatments might have on the voluntary intake by goats in Nepal of Eupatorium adenophorum, an invasive weed that is usually only consumed by goats to a very limited extent. Samples of E. adenophorum were collected and either untreated, soaked for 2 h or wilted for 2 h before being oven dried (60 degrees C) and ground. Soaking and wilting had little effect on the chemical composition of E. adenophorum, but did increase (P=0.036) its in vitro organic matter degradability, by approximately 8%. The short-term intake rate (STIR) of treated and untreated E. adenophorum was then estimated with eight goats. Soaking time (from 2 to 24 h) was not related to STIR (r = -0.111, P=0.198), but the time E. adenophorum was left to wilt (from 2 to 48h), was positively related to STIR (r=0.521, P<0.001), with values of STIR (g dry matter/min kg goat liveweight(0.75)) being 0.405, 0.649,1.058, S.E.M. 0.088 for E. adenophorum, that had been wilted for 0, 24 and 48 h respectively (P<0.001). Liveweight change of goats and voluntary intake of E. adenophorum by goats was then estimated with 24 goats. E. adenophorum was fed either unwilted, or wilted for 24 or 48 h. It was fed as the sole forage or as a 3:1 mixture (dry matter basis) with Ficus cunia. There was a linear (P<0.001) and quadratic (P<0.01) increase in the intake of total forage and E. adenophorum with wilting time of E. adenophorum. Offering Ficus cunia increased total forage intake, but decreased E. adenophorum intake (P<0.05). After four weeks, there was virtually no change in goat liveweight and no significant difference between treatments. The results suggest that wilting E adenophorum for 24 h could increase its intake by goats, and thereby increase its usefulness, as a potential source of forage in the dry season of Nepal, when forage scarcity is a common constraint to livestock production. (C) 2007 Elsevier B.V. All rights reserved.

In vitro cumulative gas production techniques: History, methodological considerations and challenges

Methodology used to measure in vitro gas production is reviewed to determine impacts of sources of variation on resultant gas production profiles (GPP). Current methods include measurement of gas production at constant pressure (e.g., use of gas tight syringes), a system that is inexpensive, but may be less sensitive than others thereby affecting its suitability in some situations. Automated systems that measure gas production at constant volume allow pressure to accumulate in the bottle, which is recorded at different times to produce a GPP, and may result in sufficiently high pressure that solubility of evolved gases in the medium is affected, thereby resulting in a recorded volume of gas that is lower than that predicted from stoichiometric calculations. Several other methods measure gas production at constant pressure and volume with either pressure transducers or sensors, and these may be manual, semi-automated or fully automated in operation. In these systems, gas is released as pressure increases, and vented gas is recorded. Agitating the medium does not consistently produce more gas with automated systems, and little or no effect of agitation was observed with manual systems. The apparatus affects GPP, but mathematical manipulation may enable effects of apparatus to be removed. The amount of substrate affects the volume of gas produced, but not rate of gas production, provided there is sufficient buffering capacity in the medium. Systems that use a very small amount of substrate are prone to experimental error in sample weighing. Effect of sample preparation on GPP has been found to be important, but further research is required to determine the optimum preparation that mimics animal chewing. Inoculum is the single largest source of variation in measuring GPP, as rumen fluid is variable and sampling schedules, diets fed to donor animals and ratios of rumen fluid/medium must be selected such that microbial activity is sufficiently high that it does not affect rate and extent of fermentation. Species of donor animal may also cause differences in GPP. End point measures can be mathematically manipulated to account for species differences, but rates of fermentation are not related. Other sources of inocula that have been used include caecal fluid (primarily for investigating hindgut fermentation in monogastrics), effluent from simulated rumen fermentation (e.g., 'Rusitec', which was as variable as rumen fluid), faeces, and frozen or freeze-dried rumen fluid (which were both less active than fresh rumen fluid). Use of mixtures of cell-free enzymes, or pure cultures of bacteria, may be a way of increasing GPP reproducibility, while reducing reliance on surgically modified animals. However, more research is required to develop these inocula. A number of media have been developed which buffer the incubation and provide relevant micro-nutrients to the microorganisms. To date, little research has been completed on relationships between the composition of the medium and measured GPP. However, comparing GPP from media either rich in N or N-free, allows assessment of contributions of N containing compounds in the sample. (c) 2005 Published by Elsevier B.V.

Inter-laboratory variation of in vitro cumulative gas production profiles of feeds using manual and automated methods

A study was conducted to estimate variation among laboratories and between manual and automated techniques of measuring pressure on the resulting gas production profiles (GPP). Eight feeds (molassed sugarbeet feed, grass silage, maize silage, soyabean hulls, maize gluten feed, whole crop wheat silage, wheat, glucose) were milled to pass a I mm screen and sent to three laboratories (ADAS Nutritional Sciences Research Unit, UK; Institute of Grassland and Environmental Research (IGER), UK; Wageningen University, The Netherlands). Each laboratory measured GPP over 144 h using standardised procedures with manual pressure transducers (MPT) and automated pressure systems (APS). The APS at ADAS used a pressure transducer and bottles in a shaking water bath, while the APS at Wageningen and IGER used a pressure sensor and bottles held in a stationary rack. Apparent dry matter degradability (ADDM) was estimated at the end of the incubation. GPP were fitted to a modified Michaelis-Menten model assuming a single phase of gas production, and GPP were described in terms of the asymptotic volume of gas produced (A), the time to half A (B), the time of maximum gas production rate (t(RM) (gas)) and maximum gas production rate (R-M (gas)). There were effects (P<0.001) of substrate on all parameters. However, MPT produced more (P<0.001) gas, but with longer (P<0.001) B and t(RM gas) (P<0.05) and lower (P<0.001) R-M gas compared to APS. There was no difference between apparatus in ADDM estimates. Interactions occurred between substrate and apparatus, substrate and laboratory, and laboratory and apparatus. However, when mean values for MPT were regressed from the individual laboratories, relationships were good (i.e., adjusted R-2 = 0.827 or higher). Good relationships were also observed with APS, although they were weaker than for MPT (i.e., adjusted R-2 = 0.723 or higher). The relationships between mean MPT and mean APS data were also good (i.e., adjusted R 2 = 0. 844 or higher). Data suggest that, although laboratory and method of measuring pressure are sources of variation in GPP estimation, it should be possible using appropriate mathematical models to standardise data among laboratories so that data from one laboratory could be extrapolated to others. This would allow development of a database of GPP data from many diverse feeds. (c) 2005 Published by Elsevier B.V.

Dichrostachys cinerea and Acacia nilotica fruits as dry season feed supplements for goats in a semi-arid environment: Summary of a DFID funded project in Zimbabwe

Indehiscent fruits of six tree species, common in Matabeleland were examined in in vitro and in vivo trials. The results for two of them, Acacia nilotica and Dichrostachys cinerea are presented here. Acacia nilotica-contained more total phenolics than D. cinerea, but less nitrogen (N) and fibre (ADF and NDF). After 48 h incubation, in vitro OMD of both species was increased by PEG and NaOH or wood ash treatment, except when NaOH or wood ash were used in combination with PEG with D. cinerea fruits. DM intake, DMD were lowest and N-retention negative in goats fed A. nilotica as supplement. However when fed a supplement of D. cinerea, untreated or treated with PEG or NaOH, digestibility and N-retention were highest, and similar to a commercial goat meal, with the untreated fruit. In a trial in which milking does were supplemented with D. cinerea fruits, for 65 before and 65 days after kidding, kid birthweight and weaning weight were increased by supplementation. Deaths of twin-born kids were lowest in the supplemented but unmilked group. Supplementation with D. cinerea fruit resulted in improved goat performance. The only treatment applied of practical significance, wood ash, is currently being tested in an in vivo study. More research is required on detoxification of tannins, especially with A. nilotica. (c) 2005 Elsevier B.V. All rights reserved.

Chemical composition and in vitro ruminal fermentation of common tree forages in the semi-arid rangelands of Swaziland

Browse plants play an important role in providing feed for livestock in semi-arid rangelands of Africa. Chemical composition and in vitro ruminal fermentation of leaves collected from Acacia burkei, Acacia tortilis, Acacia nilotica, Dichrostachys cinerea and Ehretia obtusifolia in communal grazing lands in the lowveld of Swaziland is presented. Leaves were collected from trees located on two soil types (i.e., lithosol and vertisol) in the communal land but it had no effect on the chemical composition of tree leaves. The NDFom and ADFom content were highest in D. cinerea and A. burkei and lowest in E. obtusifolia and A. nilotica. Crude protein (CP) contents ranged between 108 g/kg and 122 g/kg DM. D. cinerea had the highest Ca and Mg content, while A. tortilis had the lowest. There were marked variations in K level amongst browse species, with A. tortilis (9.1 g/kg DM) having the highest value. The P, Zn and Fe did not differ between browse species. Soil type and tree species interaction impacted in vitro fermentation parameters. Extent of fermentation, as measured by 48 h cumulative gas production, and organic matter degradability was highest in E. obtusifolia leaves and lowest in D. cinerea leaves within soil type. Fermentation efficiency, as measured by partitioning factors, was highest in A. nilotica leaves. Leaves of E. obtusifolia could be a valuable supplementary feedstuff for ruminant livestock due to its in vitro fermentation characteristics as well as low fibre and moderate CP levels. (c) 2007 Elsevier B.V. All rights reserved.