Methane emissions from enteric fermentation in dairy cows, 1990-2008

The Dutch protocol for the national inventory estimates the methane emission of the average Dutch dairy cow based on a Tier 3 approach. A dynamic, mechanistic model is used to represent the enteric fermentation processes, using annual national statistics on feed intake and feed composition as model inputs. Dutch dairy rations are based mainly on roughage (3/4 of dry matter ingested) with a high proportion of grass products (2/3 of roughage dry matter). Between 1990 and 2008, there were continuous increases in dry matter intake, milk production and enteric methane emission. Methane emission ranged from 111 to 129 kg/cow/year, and from 17.6 to 15.4 g/kg fat- and protein-corrected milk. The present study indicates that uncertainties in the feed intake level and the proportion and composition of grass products contribute to the variation in predicted methane emission. In addition, internal model equations also greatly contribute to the uncertainty (representation of rumen acidity and yield of volatile fatty acids). The greatest part of the uncertainty in the methane emission factor (kg methane/cow/year) is determined by the uncertainty in the feed intake and stoichiometry of volatile fatty acid production, while the greatest part of the uncertainty in the methane conversion factor (methane energy as % of gross energy intake) is determined by the stoichiometry of volatile fatty acid production in combination with the acidity of rumen digesta. Although the applicability of national statistics as model inputs can be investigated relatively easily in follow-up studies, physiological research with dairy cattle will be required to fully validate the current internal model equations

Evaluation of models to predict the stoichiometry of volatile fatty acid profiles in rumen fluid of lactating Holstein cows

Volatile fatty acids (VFA), produced in the rumen by microbial fermentation, are the main energy source for ruminants. The VFA profile, particularly the nonglucogenic (acetate, Ac; butyrate, Bu) to glucogenic (propionate, Pr) VFA ratio (NGR), is associated with effects on methane production, milk composition, and energy balance. The aim of this study was to evaluate extant rumen VFA stoichiometry models for their ability to predict in vivo VFA molar proportions. The models were evaluated using an independent data set consisting of 101 treatments from 24 peer-reviewed publications with lactating Holstein cows. All publications contained a full diet description, rumen pH, and rumen VFA molar proportions. Stoichiometric models were evaluated based on root mean squared prediction error (RMSPE) and concordance correlation coefficient (CCC) analysis. Of all models evaluated, the 1998 Friggens model had the lowest RMSPE for Ac and Bu (7.2 and 20.2% of observed mean, respectively). The 2006 Bannink model had the lowest RMSPE and highest CCC for Pr (14.4% and 0.70, respectively). The 2008 Bannink model had comparable predictive performance for Pr to that of the 2006 Bannink model but a larger error due to overall bias (26.2% of MSPE). The 1982 Murphy model provided the poorest prediction of Bu, with the highest RMSPE and lowest CCC (24.6% and 0.15, respectively). The 1988 Argyle and Baldwin model had the highest CCC for Ac with an intermediate RMSPE (0.47 and 8.0%, respectively). The 2006 Sveinbjörnsson model had the highest RMSPE (13.9 and 34.0%, respectively) and lowest CCC (0.31 and 0.40, respectively) for Ac and Pr. The NGR predictions had the lowest RMSPE and highest CCC in the 2 models of Bannink, whereas the lowest predictive performance was in the 2006 Sveinbjörnsson model. It appears that the type of VFA produced is not a simple linear relationship between substrate inputs and pH as currently represented. The analysis demonstrates that most rumen VFA stoichiometric approaches explain a large part of the variation in VFA molar proportions among diets, in particular for Ac, whereas predictive power for Pr and Bu differ largely among approaches. The move toward feed evaluation systems based on animal response might necessitate an improved representation of rumen fermentation, focused on improving our understanding of VFA proportions in diets that vary from the mean

Krapper bemesten gras : celwandvertering punt van zorg

Uitvoering van de mestwetgeving kan tot gevolg hebben dat grasproducten minder goed door de koe benut worden. Dat blijkt uit resultaten van proefbedrijf De Marke (V-focus februari 2009). Om vermindering van de melkproductie te voorkomen zal in de praktijk het rantsoen aangevuld worden met aangekocht (kracht)voer. Het is echter de vraag of dat een goede keuze is bij een toenemende druk om de bemesting te verminderen en om de uitstoot van ammoniak en broeikasgassen te verminderen. Logischer lijkt het om onder die omstandigheden te kiezen voor het beter benutten van het zelfgeteelde gras

Systems biology in animal sciences

Systems biology is a rapidly expanding field of research and is applied in a number of biological disciplines. In animal sciences, omics approaches are increasingly used, yielding vast amounts of data, but systems biology approaches to extract understanding from these data of biological processes and animal traits are not yet frequently used. This paper aims to explain what systems biology is and which areas of animal sciences could benefit from systems biology approaches. Systems biology aims to understand whole biological systems working as a unit, rather than investigating their individual components. Therefore, systems biology can be considered a holistic approach, as opposed to reductionism. The recently developed ‘omics’ technologies enable biological sciences to characterize the molecular components of life with ever increasing speed, yielding vast amounts of data. However, biological functions do not follow from the simple addition of the properties of system components, but rather arise from the dynamic interactions of these components. Systems biology combines statistics, bioinformatics and mathematical modeling to integrate and analyze large amounts of data in order to extract a better understanding of the biology from these huge data sets and to predict the behavior of biological systems. A ‘system’ approach and mathematical modeling in biological sciences are not new in itself, as they were used in biochemistry, physiology and genetics long before the name systems biology was coined. However, the present combination of mass biological data and of computational and modeling tools is unprecedented and truly represents a major paradigm shift in biology. Significant advances have been made using systems biology approaches, especially in the field of bacterial and eukaryotic cells and in human medicine. Similarly, progress is being made with ‘system approaches’ in animal sciences, providing exciting opportunities to predict and modulate animal traits

Modelling the lactation curve of dairy cows using the differentials of growth functions

Descriptions of entire lactations were investigated using six mathematical equations. comprising the differentials of four growth functions (logistic. Gompertz, Schumacher and Morgan) and two other equations (Wood and Dijkstra). The data contained monthly milk yield records from 70 first, 70 second and 75 third parity Iranian Holstein cows. Indicators of fit were model behavior, statistical evaluation and biologically meaningful parameter estimates and lactation features. Analysis of variance with equation, parity and their interaction as factors and with cows as replicates was performed to compare goodness of fit of the equations. The interaction of equation and parity was not significant for any statistics, which showed that there vas no tendency For one equation to fit a given parity better than other equations. Although model behaviour analysis showed better performance of growth functions than the Wood and Dijkstra equations in filling the individual lactation curves, statistical evaluation revealed that there was no significant difference between file goodness of fit of the different equations. Evaluation of lactation features showed that the Dijkstra equation was able to estimate the initial milk yield and peak yield more accurately than the other equations. Overall evaluation of the different equations demonstrated the potential of the differentials of simple empirical growth functions used in file Current study as equations for fitting monthly milk records of Holstein dairy cattle

Toevoeging van enkele onderdelen aan een dynamisch pensmodel

Het pensmodel van Dijkstra et al. (1992) werd op 3 onderdelen aangepast: een weergave werd toegevoegd voor 1. de invloed van het voeropnamepatroon en van de verkleining en passage van deeltjes op pensfermentatie bij melkkoeien; 2. de invloed van langketen vetzuren op het verloop van de pensfermentatie en omgekeerd, en 3. de vertering in de darm, de absorptie van afzonderlijke typen nutriënten uit het maagdarmkanaal, de benutting van deze nutriënten voor melkproductie en de potentiële melkproductie op deze nutriënten gegeven de melksamenstelling. De toegevoegde onderdelen en het volledige model werden geëvalueerd door een vergelijking tussen modelsimulaties en in de literatuur gerapporteerde effecten en inzichten in het functioneren van de pens. Daarnaast werden modelvoorspellingen vergeleken met gerapporteerde resultaten op enkele praktijkbedrijve

Nieuwe inzichten tijdens congres over waterkwaliteitbeleid

In Canada vergaderde de International Water Association (IWA) onlangs over de voortgang van de aanpak van diffuse bronnen, die de waterkwaliteit bedreigen. Ook vanuit Nederland was een delegatie aanwezig

Phosphorus in transition cows : A dairy cow trial on phosphorus metabolism in the transition period

The present study evaluates the effect of different dietary phosphorus (P) levels in dairy cattle during the transition period, focussing on animal performance and animal health. Overfeeding P in the dry period (185% vs. 100% of requirements) did not affect feed intake or milk yield postpartum, but decreased plasma P and Ca concentrations and increased the risk for periparturient hypocalcemia. A reduction of the dietary P content in lactation diets (70% vs. 100%) reduced the average plasma P concentration, increased plasma Ca concentration and P mobilisation and reduced faecal excretion of P. However, no negative effects on cow performance or animal health were found for diets with a P content below calculated requirements in the first eight weeks postpartum