Fergus L. Mould

A semi-automated in vitro gas production technique for ruminant feedstuff evaluation

This technical note describes the Reading Pressure Technique (RPT) ‐ an in vitro feed evaluation system based on a semi-automated gas production technique. Substrates are incubated together with buffered rumen fluid in sealed fermentation flasks. A pressure transducer, interfaced with a PC allows accumulated head-space gas pressure values to be directly entered into a spreadsheet. These pressure measurements are then used to generate gas volume estimates using a quadratic function derived from simultaneous pressure and volume measurements. Earlier attempts to derive volume from pressure resulted in predicted volume being under estimated. This discrepancy was most likely due to diffusion of head-space gases into the liquid phase, a factor not considered in Boyle’s Law, the initial relationship used. In comparison with the syringe technique (Theodorou et al., 1994), the modifications improved both the accuracy (reduced operator error) and rate at which measurements could be taken (5‐6 s per flask) greatly increasing the analytical capacity (to 336 flasks or 75 substrates per incubation series). The ability of this system to provide information not just on both rate and extent of degradation, but also fermentation efficiency and degradation kinetics offers a wide variety of applications, for example the systematic evaluation of tropical feedstuffs. In conclusion it is suggested that the simplicity, low cost and high capacity of the RPT system make it ideal for those situations where either budget constraints or the level of technical expertise required render the more complex systems inappropriate. # 1999 Published by Elsevier Science B.V. All rights reserved.

Predicting feed quality—chemical analysis and in vitro evaluation

Abstract As the ideal method of assessing the nutritive value of a feedstuff, namely offering it to the appropriate class of animal and recording the production response obtained, is neither practical nor cost effective a range of feed evaluation techniques have been developed. Each of these balances some degree of compromise with the practical situation against data generation. However, due to the impact of animal–feed interactions over and above that of feed composition, the target animal remains the ultimate arbitrator of nutritional value. In this review current in vitro feed evaluation techniques are examined according to the degree of animal–feed interaction. Chemical analysis provides absolute values and therefore differs from the majority of in vitro methods that simply rank feeds. However, with no host animal involvement, estimates of nutritional value are inferred by statistical association. In addition given the costs involved, the practical value of many analyses conducted should be reviewed. The in sacco technique has made a substantial contribution to both understanding rumen microbial degradative processes and the rapid evaluation of feeds, especially in developing countries. However, the numerous shortfalls of the technique, common to many in vitro methods, the desire to eliminate the use of surgically modified animals for routine feed evaluation, paralleled with improvements in in vitro techniques, will see this technique increasingly replaced. The majority of in vitro systems use substrate disappearance to assess degradation, however, this provides no information regarding the quantity of derived end-products available to the host animal. As measurement of volatile fatty acids or microbial biomass production greatly increases analytical costs, fermentation gas release, a simple and non-destructive measurement, has been used as an alternative. However, as gas release alone is of little use, gas-based systems, where both degradation and fermentation gas release are measured simultaneously, are attracting considerable interest. Alternative microbial inocula are being considered, as is the potential of using multi-enzyme systems to examine degradation dynamics. It is concluded that while chemical analysis will continue to form an indispensable part of feed evaluation, enhanced use will be made of increasingly complex in vitro systems. It is vital, however, the function and limitations of each methodology are fully understood and that the temptation to over-interpret the data is avoided so as to draw the appropriate conclusions. With careful selection and correct application in vitro systems offer powerful research tools with which to evaluate feedstuffs.

Misleading relationships between in situ rumen dry matter disappearance, chemical analyses and in vitro gas production and digestibility, of sugarcane bagasse treated with varying levels of electron irradiation and ammonia

Twelve samples of sugarcane bagasse, representing untreated material or bagasse irradiated with doses of 200, 400, 600, 800 and 1000 KGy in an electron accelerator and afterwards with or without 20 g/kg dry matter (DM) of NH3. These were analysed for changes in neutral detergent fibre (NDF), phenolic compound and reducing sugars content. DM disappearance was evaluated using both 48 h in situ and in vitro incubations, 0 h DM disappearance (washing losses) and in vitro volatile fatty acid (VFA) production. In situ disappearance was highly correlated with NDF (negatively), phenolic compound (positively) and reducing sugar (positively) content. However, washing losses were similarly correlated to NDF, phenolic compounds and reducing sugars, and little variation in either in vitro gas or VFA production was recorded. It is therefore concluded that the variations in situ disappearance observed were an artefact of washing losses and did not accurately reflect differences in rumen fermentability. These results may help to explain why the performance of animals, reported in the literature, offered treated bagasse is not as good as that anticipated from in situ analyses. # 1999 Elsevier Science B.V. All rights reserved.

Chemical composition and in vitro ruminal fermentation of selected grasses in the semiarid savannas of Swaziland

Little is known about the grass species type, composition and nutritive value in the semiarid savannas that sustain most of Swazilands cattle population through the seven-month-long dry season. This study was conducted to investigate the nutritional characteristics of grasses collected from two grazing areas (Big Bend and Simunye), which differed mainly in soil types. Mature grass species were harvested and evaluated for chemical composition (organic matter, neutral detergent fibre [NDF], acid detergent fibre [ADF], crude protein [CP] and minerals) and in vitro ruminal fermentation (in vitro gas production, in vitro organic matter degradability and partitioning factors). The most common grass species in the Big Bend grazing area were Bothriochloa insculpta, Cenchrus ciliaris and Urochloa mosambicensis. In the Simunye grazing area the most common species were B. insculpta, U. mosambicensis, Heteropogon contortus, Panicum deustum and P. maximum. For grasses harvested from Simunye, the most (P < 0.05) degradable (532 mg g−1 dry matter) was B. insculpta, which also had the least fibre (597 g kg−1 NDF and 351 g kg−1 ADF) and the highest CP content (79.8 g kg−1). The most common grass species harvested from the Big Bend area did not differ (P > 0.05) in their Mg, P, Cu, Fe, Zn, CP and NDF content. However, U. mosambicensis had the highest (P < 0.05) ADF content. The least fermentation efficiency (partitioning factor = 2.2 mg degradable organic matter [DOM] ml−1 gas) was observed for U. mosambicensis as a result of low DOM coupled with high cumulative gas production. It was concluded that all the grasses investigated in this study show a deficit for Ca, P and protein. Therefore, supplementation is needed to ensure maximum forage utilisation and to satisfy nutrient requirements of ruminant livestock.