J.W. Cone

Multiphasic analysis of gas production kinetics for in vitro fermentation of ruminant feeds

Recently developed time-related gas production techniques to quantify the kinetics of ruminant feed fermentation have a high resolution. Consequently, fermentation processes with clearly contrasting gas production kinetics can be identified. Parameterization of the separate processes is possible with a suitable multiphasic model and modelling method. A flexible, empirical, multiphasic model was proposed for parameterization of gas production profiles. This equation was fitted, using a two-step method, to four gas production profiles and the maximum fractional rate of substrate digestion (RM) was calculated for each phase. In the first step, the number of phases and starting values for parameters of the multiphasic model were derived from a combination of either (1) the measured cumulative gas production profile and its first (rate of gas production) and second (change in rate of gas production) derivative or (2) a fitted monophasic curve and the residuals between this curve and the observations. In the second step, the starting values were used to fit di- or triphasic models. Using Approach 1 was complicated by frequent fluctuations in the gas production rate. However, the combined graph of the fitted monophasic curve and residuals (Approach 2) gave good results for every profile. The multiphasic model fitted the profiles well. The robustness of the model declined when the number of phases was increased, underlining the importance of accurate estimations of starting values. It is argued that the model parameters and the calculated RM are useful for feed quality evaluation. The results show that mathematical description of gas production profiles requires a two-step approach and a multiphasic model.

Influence of rumen fluid and substrate concentration on fermentation kinetics measured with a fully automated time related gas production apparatus

Abstract A new fully automated time related gas production apparatus is presented to study fermentation kinetics in rumen fluid. The newly designed apparatus makes use of electronic pressure transducers in combination with electric valves to release overpressure during the incubation. In this very sensitive system, no gas accumulation and pressure build up takes place. Each valve opening represents a certain amount of gas, set at about 0.7 ml. By recording the number of valve openings in time the kinetics of degradation can be studied. The new equipment was used to study the influence of substrate concentration and source of rumen fluid on fermentation kinetics of grass, corn cob mix (CCM) and corn silage (CS). With the equipment, highly accurate cumulative gas production curves were obtained. In some cases differences between different curves could be made more comprehensive by plotting the rate of gas production against time. The gas production curves were fitted with a multi-phasic model. The shape of the gas production curve was influenced by the chemical composition of the substrate, the ration of the donor animal, the adaptation of the donor animal to a ration, the time of obtaining the rumen fluid from the donor animal and the concentration of the substrate.

Description of gas production profiles with a three-phasic model

By the introduction of new gas production equipment, using sensitive pressure transducers, producing highly accurate gas production profiles, new mathematical models were developed to describe the gas production profiles accurately as existing models did not fit the profiles satisfactorily. It has been shown previously that gas production profiles can be described mathematically by a three-phasic model. This paper shows that the different phases in the gas production profiles were caused by fermentation of the soluble fraction and the non-soluble fraction and by turnover of the microbial population. Because the gas production profiles can be divided into different phases it is possible to compare the results with the nylon bag technique and estimating the degradation rate of the soluble faction. Because the major fraction of the gas production in the blank is caused by microbial turnover, which occurs in an earlier stage of incubation in the blank than in the samples, it is discussed whether the subtraction of the blank gas production should better not be done.

Update of the Dutch protein evaluation system for ruminants: the DVE/OEB2010 system

In the current Dutch protein evaluation system (the DVE/OEB 1991 system), two characteristics are calculated for each feed: true protein digested in the intestine (DVE) and the rumen degradable protein balance (OEB). Of these, DVE represents the protein value of a feed, while OEB is the difference between the potential microbial protein synthesis (MPS) on the basis of available rumen degradable protein and that on the basis of available rumen degradable energy. DVE can be separated into three components: (i) feed crude protein undegraded in the rumen but digested in the small intestine, (ii) microbial true protein synthesized in the rumen and digested in the small intestine, and (iii) endogenous protein lost in the digestive processes. Based on new research findings, the DVE/OEB 1991 system has recently been updated to the DVE/OEB 2010 system. More detail and differentiation is included concerning the representation of chemical components in feed, the rumen degradation characteristics of these components, the efficiency of MPS and the fractional passage rates. For each chemical component, the soluble, washout, potentially degradable and truly non-degradable fractions are defined with separate fractional degradation rates. Similarly, fractional passage rates for each of these fractions were identified and partly expressed as a function of fractional degradation rate. Efficiency of MPS is related to the various fractions of the chemical components and their associated fractional passage rates. Only minor changes were made with respect to the amount of DVE required for maintenance and production purposes of the animal. Differences from other current protein evaluation systems, viz. the Cornell Net Carbohydrate and Protein system and the Feed into Milk system, are discussed.

Fungal treated lignocellulosic biomass as ruminant feed ingredient: a review.

In ruminant nutrition, there is an increasing interest for ingredients that do not compete with human nutrition. Ruminants are specialists in digesting carbohydrates in plant cell walls; therefore lignocellulosic biomass has potential in ruminant nutrition. The presence of lignin in biomass, however, limits the effective utilization of cellulose and hemicellulose. Currently, most often chemical and/or physical treatments are used to degrade lignin. White rot fungi are selective lignin degraders and can be a potential alternative to current methods which involve potentially toxic chemicals and expensive equipment. This review provides an overview of research conducted to date on fungal pretreatment of lignocellulosic biomass for ruminant feeds. White rot fungi colonize lignocellulosic biomass, and during colonization produce enzymes, radicals and other small compounds to breakdown lignin. The mechanisms on how these fungi degrade lignin are not fully understood, but fungal strain, the origin of lignocellulose and culture conditions have a major effect on the process. Ceriporiopsis subvermispora and Pleurotus eryngii are the most effective fungi to improve the nutritional value of biomass for ruminant nutrition. However, conclusions on the effectiveness of fungal delignification are difficult to draw due to a lack of standardized culture conditions and information on fungal strains used. Methods of analysis between studies are not uniform for both chemical analysis and in vitro degradation measurements. In vivo studies are limited in number and mostly describing digestibility after mushroom production, when the fungus has degraded cellulose to derive energy for fruit body development. Optimization of fungal pretreatment is required to shorten the process of delignification and make it more selective for lignin. In this respect, future research should focus on optimization of culture conditions and gene expression to obtain a better understanding of the mechanisms involved and allow the development of superior fungal strains to degrade lignin in biomass.

Fungal strain and incubation period affect chemical composition and nutrient availability of wheat straw for rumen fermentation

Eleven white-rot fungi were examined for their potency to degrade lignin and to improve the rumen fermentability of wheat straw. The straw was inoculated with the fungi and incubated under solid state conditions at 24°C for 0-49 days to determine changes in in vitro gas production and chemical composition. Results show that some fungi could degrade lignin by as much as 63%, yet the delignification was highly correlated with the degradation of hemicellulose (r=0.96). Reduction in lignin was poorly (r=0.47), but the ratio between lignin and cellulose loss was strongly (r=0.87) correlated with the increase in gas production. Treatment with Ceriporiopsis subvermispora for 49 days increased total gas production of the straw from 200 to 309 ml/g organic matter (OM). It was concluded that some fungi highly selective for lignin and not for cellulose are able to improve the nutritive value of wheat straw as a ruminant feed.

Nutritive value of maize silage in relation to dairy cow performance and milk quality

Maize silage has become the major forage component in the ration of dairy cows over the last few decades. This review provides information on the mean content and variability in chemical composition, fatty acid (FA) profile and ensiling quality of maize silages, and discusses the major factors which cause these variations. In addition, the effect of the broad range in chemical composition of maize silages on the total tract digestibility of dietary nutrients, milk production and milk composition of dairy cows is quantified and discussed. Finally, the optimum inclusion level of maize silage in the ration of dairy cows for milk production and composition is reviewed. The data showed that the nutritive value of maize silages is highly variable and that most of this variation is caused by large differences in maturity at harvest. Maize silages ensiled at a very early stage (dry matter (DM) < 250 g kg(-1)) were particularly low in starch content and starch/neutral detergent fibre (NDF) ratio, and resulted in a lower DM intake (DMI), milk yield and milk protein content. The DMI, milk yield and milk protein content increased with advancing maturity, reaching an optimum level for maize silages ensiled at DM contents of 300-350 g kg(-1), and then declined slightly at further maturity beyond 350 g kg(-1). The increases in milk (R(2) = 0.599) and protein (R(2) = 0.605) yields with maturity of maize silages were positively related to the increase in starch/NDF ratio of the maize silages. On average, the inclusion of maize silage in grass silage-based diets improved the forage DMI by 2 kg d(-1), milk yield by 1.9 kg d(-1) and milk protein content by 1.2 g kg(-1). Further comparisons showed that, in terms of milk and milk constituent yields, the optimum grass/maize silage ratio depends on the quality of both the grass and maize silages. Replacement of grass silage with maize silage in the ration, as well as an increasing maturity of the maize silages, altered the milk FA profile of the dairy cows, notably, the concentration of the cis-unsaturated FAs, C18:3n-3 and n-3/n-6 ratio decreased in milk fat. Despite variation in nutritive value, maize silage is rich in metabolizable energy and supports higher DMI and milk yield. Harvesting maize silages at a DM content between 300 and 350 g kg(-1) and feeding in combination with grass silage results in a higher milk yield of dairy cows.

The influence of ageing on cell wall composition and degradability of three maize genotypes.

Stem segments of the maize (Zea mavs L.) hybrids LGH, Eta Ipho (EI) and a brown midrib mutant. INRA 260 bm3 (bm3) were freeze-dried, ground and analysed for cell wall content, hemicellulose, cellulose, lignin and in vitro cell wall degradability with rumen fluid. Stem cross-sections, stained with acid phloroglucinol (AP) and chlorine sulphite (CS) showed an increased intensity in staining during maturation, but no considerable difference in staining intensity was observed between genotypes. The lignin content increased during maturation with evidently less lignin in bm3 than in EI and LGH. However, cell wall degradability did not differ between the older stem segments of EI and bm3, although the amount of lignin in LGH was twice that of bm3. It can be concluded that an increase in lignin content occurs simultancously with a decrease in cell wall degradability within a genotype. However, between different genotypes the lignin content is not an indicator of degree of cell wall degradability.

Effect of fungal treatments of fibrous agricultural by-products on chemical composition and in vitro rumen fermentation and methane production

Maize stover, rice straw, oil palm fronds and sugarcane bagasse were treated with the white-rot fungi Ceriporiopsis subvermispora, Lentinula edodes, Pleurotus eryngii, or Pleurotus ostreatus at 24 °C for 0-6 weeks. The fungi increased total gas production from oil palm fronds by 68-132%, but none of the fungi improved the in vitro rumen fermentability of maize stover. C. subvermispora and L. edodes increased total gas production of sugarcane bagasse by 65-71%, but P. eryngii and P. ostreatus decreased it by 22-50%. There was a linear relationship (P<0.05) between the proportion of lignin in the original substrate and the increase in in vitro gas production observed for C. subvermispora and L. edodes treatments (R2=0.92 and 0.96, respectively). It is concluded that C. subvermispora and L. edodes have a particularly high potential to improve the nutritive value of highly lignified ruminant feeds.

Effects of forage maize type and maturity stage on in vitro rumen fermentation characteristics

An experiment with forage maize plants representing early and late-ripening types of Dry Down and Stay Green cultivar types was conducted to study the effects of cultivar and maturity stage on in vitro rumen fermentation characteristics and to investigate the validity of the generally supposed qualities of these cultivars. Plants were harvested at an estimated whole plant dry matter (DM) content of 250, 320 or 390 g kg‾1, on 20 August, 16 September and 3 October 2003, respectively. Chemical composition and in vitro rumen fermentation characteristics, using the gas production technique, were determined of samples from entire not ensiled plants, ears and stover and from entire plants after ensiling. The increase in whole plant DM content from 250 to 320 g kg%sup-1; (20 August - 16 September) caused starch content of the whole plants to increase and neutral detergent fibre (NDF) digestibility to decrease, both more than prolonged ripening (to 390 g DM kg-1). DM content at harvest had a statistically significant influence on degree and rate of in vitro rumen fermentation. Calculated in vitro starch degradation after 10 h of incubation in rumen fluid suggested an increased content of rumen escape starch in the older samples. Maize type had only minor effects on fermentation characteristics, which were most pronounced for the ears and the remaining stover. Although the observed differences caused by the Dry Down or Stay Green characteristics were statistically significant in some cases, they were not systematic not for the early nor for the late-ripening types.