Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    The genetic background of bovine αs1- and αs2-casein phosphorylation
    Fang, Zih-Hua - \ 2017
    Wageningen University. Promotor(en): E. Verrier; H. Bovenhuis, co-promotor(en): P. Martin; M.H.P.W. Visker. - Wageningen : Wageningen University - ISBN 9789463438148 - 141
    dairy cattle - alpha-s1-casein - alpha-s2-casein - phosphorylation - milk composition - milk proteins - genetic variation - genetic factors - animal genetics - melkvee - alfa-s-1-caseïne - alfa-s-2-caseïne - fosforylering - melksamenstelling - melkeiwitten - genetische variatie - genetische factoren - diergenetica

    Phosphorylation of caseins (CN) is a crucial post-translational modification allowing caseins to aggregate as micelles. The formation and stability of casein micelles are important for transporting abundant minerals to the neonate and manufacturing of dairy products. Therefore, it is of great interest to explore variation in degrees of phosphorylation of caseins and study to what extent genetic and other factors contribute to this variation. This thesis aimed to investigate the genetic background of bovine milk protein composition with a focus on phosphorylation of αs1- and αs2-CN. Two studies were conducted to quantify phosphorylation levels of αs1- and αs2-CN: one in French Montbéliarde using liquid chromatography coupled with electrospray ionization mass spectrometry and the other in Dutch Holstein Friesian using capillary zone electrophoresis. In French Montbéliarde, in addition to the known isoforms αs1-CN-8P and-9P and αs2-CN-10P to -13P, three new phosphorylation isoforms were detected, namely αs2-CN-9P, αs2-CN-14P, and αs2-CN-15P. Relative concentrations of the phosphorylation isoforms varied considerably among cows. Phenotypic correlations showed that isoforms phosphorylated at higher degrees (αs1-CN-9P and αs2-CN-12P to -14P) correlated negatively with isoforms phosphorylated at lower degrees (αs1-CN-8P, αs2-CN-10P, and -11P). Furthermore, it was shown that αs1- and αs2-CN phosphorylation profiles changed across parity and lactation, and exploitable genetic variation for the phosphorylation degrees of αs1- and αs2-CN (defined as the proportion of higher-degree isoforms in αs1- and αs2-CN, respectively) exist. In Dutch Holstein Friesian, three αs2-CN isoforms, namely αs2-CN-10P to -12P, and the phosphorylation degrees of αs1- and αs2-CN were quantified. High intra-herd heritabilities were estimated for individual αs2-CN phosphorylation isoforms and the phosphorylation degrees of αs1- and αs2-CN (ranging from 0.54 to 0.89). This suggests that genetic factors contribute substantially to observed differences in αs1- and αs2-CN phosphorylation profiles. The highly positive correlation between the phosphorylation degrees of αs1- and αs2-CN (0.94) suggest that phosphorylation of αs1- and αs2-CN is related. Additionally, a total of 10 regions, distributed across Bos taurus autosomes (BTA) 1, 2, 6, 9, 11, 14, 15, 18, 24 and 28, were detected to be associated with individual αs1- and αs2-CN phosphorylation isoforms and their phosphorylation degrees. Regions on BTA1, 6, 11 and 14 were associated with multiple traits studied. Two quantitative trait loci (QTL) regions were detected on BTA1: one affecting αs2-CN production, and the other affecting αs1-CN PD and αs2-CN PD. The QTL region on BTA6 affected only individual αs2-CN isoforms. The QTL region on BTA11 and 14 affected relative concentrations of αs2-CN-10P and αs2-CN-11P, αs1-CN PD and αs2-CN PD. Results suggested that effects of identified genomic regions on αs1-CN PD and αs2-CN PD are probably due to changes in milk synthesis and phosphorus secretion in milk.

    Predicting methane emission of dairy cows using milk composition
    Gastelen, Sanne van - \ 2017
    Wageningen University. Promotor(en): W.H. Hendriks, co-promotor(en): J. Dijkstra; K.A. Hettinga. - Wageningen : Wageningen University - ISBN 9789463437097 - 266
    dairy cows - dairy cattle - methane production - emission - milk composition - fatty acids - cattle feeding - fermentation - nutrition physiology - animal nutrition - pollution - melkkoeien - melkvee - methaanproductie - emissie - melksamenstelling - vetzuren - rundveevoeding - fermentatie - voedingsfysiologie - diervoeding - verontreiniging

    Enteric methane (CH4) is produced as a result of microbial fermentation of feed components in the gastrointestinal tract of ruminant livestock. Methane has no nutritional value for the animal and is predominately released into the environment through eructation and breath. Therefore, CH4 not only represents a greenhouse gas contributing to global warming, but also an energy loss, making enteric CH4 production one of the main targets of greenhouse gas mitigation practices for the dairy industry. Obviously, reduction of CH4 emission could be achieved by simply reducing livestock numbers. However, the global demand for dairy products has been growing rapidly and is expected to further grow in the future. Therefore, it is critical to minimize environmental impact to produce high-quality dairy products. The overall aim of this PhD research was, therefore, to develop a proxy for CH4 emission that can be measured in milk of dairy cows.

    There are currently a number of potentially effective dietary CH4 mitigation practices available for the livestock sector. The results of Chapter 3 show that replacing fiber-rich grass silage with starch-rich corn silage in a common forage-based diet for dairy cattle offers an effective strategy to decrease enteric CH4 production without negatively affecting dairy cow performance, although a critical level of starch in the diet seems to be needed. Little is known whether host genetics may influence the CH4 emission response to changes in diet. Therefore, the interaction between host DGAT1 K232A polymorphism with dietary linseed oil supplementation was evaluated in Chapter 7. The results of Chapter 7 indicate that DGAT1 K232A polymorphism is associated with changes in milk composition, milk N efficiency, and diet metabolizability, but does not affect digestibility and enteric CH4 emission, whereas linseed oil reduces CH4 emission independent of the DGAT1 K232A polymorphism.

    Accurate and repeatable measurements of CH4 emission from individual dairy cows are required to assess the efficacy of possible mitigation strategies. There are several techniques to estimate or measure enteric CH4 production of dairy cows, including climate respiration chambers, but none of these techniques are suitable for large scale precise and accurate measurements. Therefore, the potential of various metabolites in milk, including milk fatty acids (MFA), as a proxy (i.e., indicators or animal traits that are correlated with enteric CH4 production) for CH4 emission of dairy cows gained interest. Until recently, gas chromatography was the principal method used to determine the MFA profile, but this technique is unsuitable for routine analysis. This has led to the application of Fourier-transform infrared spectroscopy (FTIR) for determination of the MFA profile. Chapter 2 provides an overview of the recent research that relates MFA with CH4 emission, and discusses the opportunities and limitations of using FTIR to estimate, indirectly via MFA or directly, CH4 emission of dairy cattle. The recent literature on the relationship between MFA and CH4 emission gives inconsistent results. Where some studies found a clear and strong relation, other studies consider MFA to be unreliable predictors for CH4 emitted by dairy cows. Even the studies that do find a clear relation between MFA and CH4 emissions do not describe similar prediction models using the same MFA. These discrepancies can be the result of many factors, including dietary composition and lactation stage. Additionally, literature showed that the major advantages of using FTIR to predict CH4 emission include its simplicity and potential practical application on a large scale. Disadvantages include the inability to predict important MFA for the prediction of CH4 emission, and the moderate power of FTIR to directly predict CH4 emission. The latter was also demonstrated in Chapter 9, in which the CH4 prediction potential of MFA was compared with that of FTIR using data from 9 experiments (n = 218 individual cow observations) covering a broad range of roughage-based diets. The results indicate that MFA have a greater potential than FTIR spectra to estimate CH4 emissions, and that both techniques have potential to predict CH4 emission of dairy cows, but also limited current applicability in practice. Much focus has been placed on the relationship between MFA and CH4 emission, but milk also contains other metabolites, such as volatile and non-volatile metabolites. Currently, milk volatile metabolites have been used for tracing animal feeding systems and milk non-volatile metabolites were shown to be related to the health status of cows. In Chapter 4, the relationship between CH4 emission and both volatile and non-volatile metabolites was investigated, using data and milk samples obtained in the study described in Chapter 3. In general, the non-volatile metabolites were more closely related to CH4 emissions than the volatile metabolites. More specifically, the results indicate that CH4 intensity (g/kg fat- and protein-corrected milk; FPCM) may be related to lactose synthesis and energy metabolism in the mammary gland, as reflected by the milk non-volatile metabolites uridine diphosphate-hexose B and citrate. Methane yield (g/kg dry matter intake) on the other hand, may be related to glucogenic nutrient supply, as reflected by the milk non-volatile acetone. Based on the metabolic interpretations of these relationships, it was hypothesized that the addition of both volatile and non-volatile metabolites in a prediction model with only MFA would enhance its predictive power and, thus, leads to a better proxy in milk for enteric CH4 production of dairy cows. This was investigated in Chapter 5, again using data and milk samples described in Chapter 3. The results indicate that MFA alone have moderate to good potential to estimate CH4 emission. Furthermore, including volatile metabolites (CH4 intensity only) and non-volatile metabolites increases the CH4 emission prediction potential.

    The work presented in Chapters 3, 4 and 5, was based upon a small range of diets (i.e., four roughage-based diets in which grass silage was replaced partly or fully by corn silage) of one experiment. Therefore, in Chapter 6, the relationship between CH4 emission and the milk metabolome in dairy cattle was further quantified. Data (n = 123 individual cow observations) were used encompassing a large of roughage-based diets, with different qualities and proportions of grass, grass silage and corn silage. The results show that changes in individual milk metabolite concentrations can be related to the ruminal CH4 production pathways. These relationships are most likely the result from changes in dietary composition that affect not only enteric CH4 production, but also the profile of volatile and non-volatile metabolites in milk. Overall, the results indicate that both volatile and non-volatile metabolites in milk might provide useful information and increase our understanding of CH4 emission of dairy cows. However, the development of CH4 prediction models revealed that both volatile and non-volatile metabolites in milk hold little potential to predict CH4 emissions despite the significant relationships found between individual non-volatile metabolites and CH4 emissions. Additionally, combining MFA with milk volatile metabolites and non-volatile metabolites does not improve the CH4 prediction potential relative to MFA alone. Hence, it is concluded that it is not worthwhile to determine the volatile and non-volatile metabolites in milk in order to estimate CH4 emission of dairy cows.

    Overall, in comparison with FTIR, volatile and non-volatile metabolites, the MFA are the most accurate and precise proxy in milk for CH4 emission of dairy cows. However, most of MFA-based models to predict CH4 emission tend to be accurate only for the production system and the environmental conditions under which they were developed. In Chapter 8 it was demonstrated that previously developed MFA-based prediction equations did not predict CH4 emission satisfactory of dairy cows with different DGAT1 genotypes or fed diets with or without linseed oil. Therefore, the greatest shortcoming today of MFA-based CH4 prediction models is their lack of robustness. Additionally, MFA have restricted practical application, meaning that most MFA retained in the current CH4 prediction models cannot be determined routinely because of the use of gas chromatography. The MFA that can be determined with the use of infrared spectroscopy are however no promising predictors for CH4 emission. Furthermore, MFA have only a moderate CH4 prediction potential. This together suggests that it might not be the best option to focus in the future on MFA alone as a proxy for CH4 emission of dairy cows.

    The FTIR technique has a low to moderate CH4 prediction potential. However, FTIR has a great potential for practical high throughput application, facilitating repeated measurements of the same cow potentially reducing random noise. Results of this thesis also demonstrated that FTIR spectra do not have the potential to detect differences in CH4 emission between diets which are, in terms of forage level and quality, commonly fed in practice. Moreover, the robustness of FTIR spectra is currently unknown. Hence, it remains to be investigated whether FTIR spectra can predict CH4 emissions from dairy cows housed under different conditions from those under which the FTIR-based prediction equations were developed. It is therefore concluded that the accuracy and precision to predict CH4 emission using FTIR needs to increase, and the capacity of FTIR to evaluate the differences in CH4 emission between dairy cows and different types of diets needs to improve, in order to actually be a valuable proxy for CH4 emission of dairy cows.

    Dry period length of dairy cows : milk composition and quality
    Vries, Ruben de - \ 2017
    Wageningen University. Promotor(en): Toon van Hooijdonk; K. Holtenius, co-promotor(en): Kasper Hettinga; H.L.M. Lindmark-Månsson. - Wageningen : Wageningen University - ISBN 9789463430463 - 141
    dairy cows - dry period - milk composition - milk quality - milk - casein - micelles - melkkoeien - gustperiode - melksamenstelling - melkkwaliteit - melk - caseïne - micellen

    A dry period of dairy cows is historically seen as a period during which the cow can restore its body condition and regenerate its mammary epithelium in order to be high yielding in the successive lactation. Recent work has indicated that high yielding cows generally experience a severe negative energy balance in early lactation. Dry period reduction is a strategy to improve the energy balance of dairy cows in early lactation. This thesis aimed at evaluating the influence of dry period length on milk composition and milk quality. Milk composition parameters indicate the processing quality of milk for the dairy plant, and may also reflect the physiological condition and energy status of the cow.

    In this work, omission of the dry period was related to a reduced β-casein fraction in early lactation milk. Applying a short (4 weeks) instead of a conventional (8 weeks) dry period resulted in increased plasmin activity in milk, but did not affect the β-casein fraction. Increased plasmin activity in relation to a shortened dry period was particularly found in milk of cows of third or higher parity, that generally had relatively high somatic cell count. At low somatic cell counts, dry period reduction or omission only tended to result in an increased plasmin activity due a higher casein concentration in milk. From increased concentrations of a number of low abundant proteins in colostrum of cows with a short dry period it was hypothesized that a short dry period was related to increased proliferation of mammary epithelial cells during the first days in lactation.

    Although the casein composition of milk was related to both plasmin activity in milk and the metabolic status of cows, which are both influenced by dry period length, quantitative differences in casein composition of cows with different dry period length were small. It was concluded that shortening or omitting the dry period of cows with good mammary health obtains milk with a higher protein content with little differences in protein composition.

    Low Emission Feed : using feed additives to decrease methane production in dairy cows
    Klop, G. - \ 2016
    Wageningen University. Promotor(en): Wouter Hendriks, co-promotor(en): Jan Dijkstra; Andre Bannink. - Wageningen : Wageningen University - ISBN 9789462578944 - 168
    feeds - emission - feed additives - dairy cows - methane production - nitrates - docosahexaenoic acid - milk composition - voer - emissie - voedertoevoegingen - melkkoeien - methaanproductie - nitraten - docosahexaeenzuur - melksamenstelling

    Research into manipulating methane (CH4) production as a result of enteric fermentation in ruminants currently receives global interest. Using feed additives may be a feasible strategy to mitigate CH4 as they are supplied in such amounts that the basal diet composition will not be largely affected. The latter is relevant because ruminants have the capacity to convert human inedible feedstuffs into human edible energy and protein. However, the application of CH4 mitigation feed additives may be hampered by several negative side effects including trade-offs with other environmental impacts, negative effects on animal performance, and lack of persistency of the mitigating effect. The research described in this thesis addresses both the mitigating effect of feed additives as well as its persistency. The main focus was on investigating additivity of the CH4 mitigating effect of feed additives, on the adaptation of rumen microbes to long term feeding of feed additives, and on exploring the potential of rotational feeding of additives to avoid (or reduce) microbial adaptation.

    In an experiment with lactating dairy cows in climate respiration chambers to study potential interactions between the effects of feeding nitrate and docosahexaenoic acid (DHA; C22:6 n-3) on enteric CH4 production, the effects of nitrate and DHA on CH4 yield [g/kg dry matter intake (DMI)] and CH4 intensity [g/kg fat- and protein- corrected milk (FPCM)], were additive (Chapter 2). Nitrate decreased CH4 irrespective of the unit in which it was expressed, and the average decline in CH4 emission corresponds to 85% of the stoichiometric potential of nitrate to decrease CH4. Feeding DHA had no effect on CH4 yield, but resulted in a higher CH4 intensity, because of milk fat depression. The interaction effect between nitrate and DHA on fiber digestibility indicated that negative effects of nitrate on apparent total tract digestibility of nutrients were alleviated by DHA, probably due to an altered feed intake pattern.

    Using an isotope measurement protocol in the same study, it was demonstrated that effects of nitrate as a CH4 mitigating feed additive on fiber degradation in the rumen can be detected by evaluating diurnal patterns of 13C enrichment of exhaled CO2 (Chapter 3). Feeding nitrate, but not DHA, resulted in a pronounced increase in 13C enrichment of CO2 in the first 3 to 4 h after feeding only. Results support the hypothesis that effects of a feed additive on the rate of fiber degradation in the rumen can be detected by evaluating diurnal patterns of 13C enrichment of CO2. A prerequisite for this detection method is that the main ration components differ in natural 13C enrichment (e.g., C3 and C4 plants), and in content of the nutrients that are expected to be involved in a shift in fermentation (e.g., starch and fiber) or in degradability of a nutrient.

    In a combined in vivo and in vitro trial, the adaptation to CH4 mitigating feed additives, viz. an essential oil blend or lauric acid (C12:0), compared with a control diet was first investigated using the in vitro gas production technique during the period that lactating cows were adapting to certain feed additives (Chapter 4). Rumen fluid was collected from each cow at several days relative to the introduction of the additives in the diets and used as inoculum for the gas production experiment with each of the three different substrates that reflected the treatment diets offered to the cows. The feed additives in the donor cow diet had a stronger effect on in vitro gas and CH4 production than the same additives in the incubation substrate. From day 4 onwards, the C12:0 diet persistently reduced gas and CH4 production, total volatile fatty acid concentration, acetate molar proportion and in vitro organic matter degradation, and increased propionate molar proportion. In contrast, in vitro CH4 production was reduced by the essential oils diet on day 8, but not on days 15 and 22. In line with these findings, the molar proportion of propionate in fermentation fluid was higher, and that of acetate smaller, for the essential oils diet than for the control diet on day 8, but not on days 15 and 22. Overall, the data indicate a transient effect of the essential oils on CH4 production, which may indicate microbial adaptation, whereas the CH4 mitigating effect of C12:0 persisted. It is recommended that this phenomenon is considered in the planning of future studies on the mitigation potential of feed additives in vitro.

    In a follow-up in vivo study, it was investigated whether the alternate feeding of two CH4 mitigating feed additives with a different mode of action (viz. C12:0 and a blend of essential oils) would result in a persistently lower CH4 production compared to feeding a single additive over a period of 10 weeks. The experiment comprised a pre-treatment period and three two-week measurement periods, with two periods of 2 weeks in between in which CH4 emission was not measured. Cows received either continuously the essential oil blend, or both the essential oil blend and C12:0 following a weekly rotation schedule (Chapter 5). Both CH4 yield and CH4 intensity changed over time, but were not affected by treatment. Methane yield and intensity were significantly lower (12 and 11%, respectively) in period 1 compared with the pre-treatment period, but no significant difference relative to the pre-treatment period was observed in period 3 (numerically 9 and 7% lower, respectively) and in period 5 (numerically 8 and 4% lower, respectively). These results indicate a transient decrease in CH4 yield and intensity in time, but no improvement in extent or persistency of CH4 reduction due to rotational feeding of essential oils and C12:0 in lactating dairy cows. However, there were indications that the concept of rotation may be effective and warrants further investigation.

    The additives and concepts tested in this thesis are applied under specific experimental conditions. More mechanistic understanding is required to predict the response of the same additives when supplemented to other basal diets or cows in a different physiological state. Trade-offs in environmental impact, and effects on cow health and performance, and on milk processing parameters and food safety are important aspects to consider in future research on the application of feed additives as CH4 mitigation strategy.

    Mapping and fine-mapping of genetic factors affecting bovine milk composition
    Duchemin, S.I. - \ 2016
    Wageningen University. Promotor(en): Johan van Arendonk, co-promotor(en): Henk Bovenhuis; Marleen Visker; Willem F. Fikse. - Wageningen : Wageningen University - ISBN 9789462577305 - 190
    dairy cows - dairy cattle - milk composition - milk fat - genetic factors - quantitative trait loci - genomics - genetic mapping - animal genetics - melkkoeien - melkvee - melksamenstelling - melkvet - genetische factoren - loci voor kwantitatief kenmerk - genomica - genetische kartering - diergenetica

    Duchemin, S.I. (2016). Mapping and fine-mapping of genetic factors affecting bovine milk composition. Joint PhD thesis, between Swedish University of Agricultural Sciences, Sweden and Wageningen University, the Netherlands

    Bovine milk is an important source of nutrients in Western diets. Unraveling the genetic background of bovine milk composition by finding genes associated with milk-fat composition and non-coagulation of milk were the main goals of this thesis. In Chapter 1, a brief description of phenotypes and genotypes used throughout the thesis is given. In Chapter 2, I calculated the genetic parameters for winter and summer milk-fat composition from ~2,000 Holstein-Friesian cows, and concluded that most of the fatty acids (FA) can be treated as genetically the same trait. The main differences between milk-fat composition between winter and summer milk samples are most likely due to differences in diets. In Chapter 3, I performed genome-wide association studies (GWAS) with imputed 777,000 single nucleotide polymorphism (SNP) genotypes. I targeted a quantitative trait locus (QTL) region on Bos taurus autosome (BTA) 17 previously identified with 50,000 SNP genotypes, and identified a region covering 5 mega-base pairs on BTA17 that explained a large proportion of the genetic variation in de novo synthesized milk FA. In Chapter 4, the availability of whole-genome sequences of keys ancestors of our population of cows allowed to fine-mapped BTA17 with imputed sequences. The resolution of the 5 mega base-pairs region substantially improved, which allowed the identification of the LA ribonucleoprotein domain family, member 1B (LARP1B) gene as the most likely candidate gene associated with de novo synthesized milk FA on BTA17. The LARP1B gene has not been associated with milk-fat composition before. In Chapter 5, I explored the genetic background of non-coagulation of bovine milk. I performed a GWAS with 777,000 SNP genotypes in 382 Swedish Red cows, and identified a region covering 7 mega base-pairs on BTA18 strongly associated with non-coagulation of milk. This region was further characterized by means of fine-mapping with imputed sequences. In addition, haplotypes were built, genetically differentiated by means of a phylogenetic tree, and tested in phenotype-genotype association studies. As a result, I identified the vacuolar protein sorting 35 homolog, mRNA (VPS35) gene, as candidate. The VPS35 gene has not been associated to milk composition before. In Chapter 6, the general discussion is presented. I start discussing the challenges with respect to high-density genotypes for gene discovery, and I continue discussing future possibilities to expand gene discovery studies, with which I propose some alternatives to identify causal variants underlying complex traits in cattle.

    Dynamics of the proteome in human and farm animal milk
    Zhang, L. - \ 2015
    Wageningen University. Promotor(en): Toon van Hooijdonk, co-promotor(en): Kasper Hettinga; Jacques Vervoort. - Wageningen : Wageningen University - ISBN 9789462574199 - 193
    moedermelk - melk - kamelenmelk - proteomen - melkeiwit - melkeiwitten - lactatie - melksamenstelling - melkbewerking - kwantitatieve analyse - kwalitatieve analyse - human milk - milk - camel milk - proteomes - milk protein - milk proteins - lactation - milk composition - milk processing - quantitative analysis - qualitative analysis

    Abstract

    The milk proteome changes due to many factors, such as lactation, individual, health status, processing, and species differences. The objective of the work described in this thesis was to increase our understanding of the dynamics of proteome in human and farm animal milk, and its contributions on the improvement of infant formula. This study shows that milk proteome not only differs qualitatively and quantitatively but also differs in their changing rate over lactation between species, especially for immune-related proteins. In addition, milk proteome shows different stability under different processing within and between species. It is concluded that although milk proteome differs between species, the function of milk proteins is essentially the same for all newborns, in providing nutrients and immunity for their growth and development. Both enriching specific milk proteins and mild processing of milk proteins should be considered for the improvement of infant formula.

    Natural variation in casein composition of milk
    Bijl, E. - \ 2014
    Wageningen University. Promotor(en): Toon van Hooijdonk, co-promotor(en): T. Huppertz; Hein van Valenberg. - Wageningen : Wageningen University - ISBN 9789461739445 - 145
    melk - caseïne - melksamenstelling - variatie - milk - casein - milk composition - variation

    Bovine milk contains 3-4 % protein and almost 80% of the milk protein fraction consist of four caseins; αs1-casein, β-casein, αs2-casein and κ-casein. Most of the caseins in milk are assembled in casein micelles, which consist of several thousands of individual casein molecules and salts. The unique structure of casein micelles allows the delivery of large amounts of calcium and phosphate to the neonate. Considerable natural variation in casein content and composition exists between milk samples from individual cows, however the impact of these variations on casein micelle structure and technological properties of dairy products are largely unknown. This study showed that the expression of caseins and their post-translational modification as well as inclusion of calcium in casein micelles are well-balanced processes. Analysis of the genetic background of phosphorylation of αs1-casein with eight or nine phosphate groupsshowed that αs1-casein phosphorylation was regulated by a different set of genes. Also, variation in αs1-casein phosphorylation resulted in changes in the core of casein micelles and was associated with a difference in degradation efficiency by chymosin in milk gels. Another post-translational modification, glycosylation of κ-casein, resulted in changes in the surface of casein micelles. Natural variation in αs1-CN phosphorylationand glycosylation of κ-casein are both relevant factors to consider for optimization of dairy products and the design of future breeding strategies.

    Stikstofverliezen beter inschatten
    Spek, J.W. ; Bannink, A. ; Dijkstra, J. - \ 2013
    Veeteelt 30 (2013)17. - ISSN 0168-7565 - p. 20 - 22.
    melkveehouderij - stikstofverliezen - excretie - melksamenstelling - ureum - melkveevoeding - voersamenstelling - eiwitgehalte - dairy farming - nitrogen losses - excretion - milk composition - urea - dairy cattle nutrition - feed formulation - protein content
    Hoe kan het melkureumgehalte beter worden benut als maat voor stikstofverliezen in de urine? Onderzoekers van WUR concluderen dat stikstofverliezen in de urine beter zijn in te schatten met een combinatie van factoren, zoals het melkureumgehalte en het zout- en eiwitgehalte in het rantsoen.
    The biology of milk synthesis from a proteomics perspective
    Lu, J. - \ 2013
    Wageningen University. Promotor(en): Toon van Hooijdonk, co-promotor(en): Kasper Hettinga; Jacques Vervoort. - S.l. : s.n. - ISBN 9789461734600 - 177
    melksynthese - melksecretie - melksamenstelling - oppervlakte-eiwitten - eiwitexpressieanalyse - variatie - milk synthesis - milk secretion - milk composition - surface proteins - proteomics - variation

    Large variation in bovine milk composition of Dutch Holstein cows has been observed. The factors influencing the milk synthesis and secretion process in the mammary gland and the variations in this process lead to variation in milk composition. The understanding of milk synthesis was improved during the last decades, however, much is still unknown, especially with regard to lipid synthesis and secretion. In this research, a proteomics technique (FASP-Dimethyl labeling-NanoLC-Orbitrap-MS/MS) was used to identify and quantify low abundant proteins in milk. By using this proteomics technique combined with a metabolomics technique (1H-NMR), the variation in milk synthesis and secretion processes were shown as affected by several factors influencing milk composition: DGAT1 polymorphism, fat globule size and energy balance of the cow. Stomatin, cholesterol and cholesterol synthesis enzymes were shown to be important for milk synthesis and secretion in lactating cows in all the different studies. Cytoplasmic vesicle and cytoskeleton proteins were shown to be involved in milk fat globule secretion. These results led to new insights in milk synthesis and secretion.

    Gezondheidsraad onderschat rendement van de Nederlandse koe : simpele rekensom weerlegt eiwitfabel over melk
    Dijkstra, Jan - \ 2011
    dairy cows - milk products - milk composition - milk production characteristics - nutrients - nutrient content - nutrient sources
    Sturen in melkproductie en melksamenstelling : verkennende studie naar de effecten van Clinoptiloliet
    Verwer, C.M. ; Eekeren, N.J.M. van - \ 2011
    [S.l.] : Louis Bolk Instituut (Biogeit rapport / Louis Bolk Instituut 23) - 25 p.
    geitenhouderij - clinoptiloliet - voedertoevoegingen - melkproductie - melksamenstelling - biologische landbouw - goat keeping - clinoptilolite - feed additives - milk production - milk composition - organic farming
    In dit Biogeit rapport wordt een praktijkonderzoek beschreven naar de effecten van Clinoptiloliet op de melkproductie en melksamenstelling van geiten. Voor het onderzoek zijn 50 nieuwmelkte geiten gebruikt. De geiten werden verdeeld over 2 groepen; een controle-groep en een Clinoptiloliet-groep. Clinoptiloliet werd verstrekt nadat alle dieren minimaal 6 weken in lactatie waren. Gedurende 6 maanden zijn om de 6 weken melkmonsters genomen om per individu de melkproductie, vetgehalte en eiwitgehalte te bepalen. Bij de start van het onderzoek en aan het einde van het onderzoek is ook het celgetal per geit bepaald. Clinoptiloliet had geen (neven)effect op de melkproductie en het eiwitgehalte van de melk. Clinoptiloliet had een positief verhogend effect op het vetgehalte van de melk met ongeveer 0.1-0.4 %.
    Melk voorspelt dracht (interview)
    Woelders, Henri ; Haas, Yvette de - \ 2011
    dairy farming - dairy cows - gestation period - milk composition - milk proteins - measurement
    Fate of fatty acids during ensiling: relationship with milk fat composition of dairy cows
    Khan, N.A. - \ 2011
    Wageningen University. Promotor(en): Wouter Hendriks, co-promotor(en): John Cone; V. Fievez. - [S.l.] : S.n. - ISBN 9789085859581 - 158
    melkkoeien - melkvet - melksamenstelling - vetzuren - kuilvoerbereiding - graskuilvoer - maïskuilvoer - stabiliteit - voer - ruwvoer (forage) - rundveevoeding - diervoeding - dairy cows - milk fat - milk composition - fatty acids - silage making - grass silage - maize silage - stability - feeds - forage - cattle feeding - animal nutrition

    Transition of dairy cows from grazing to silage based rations significantly increases the saturated: unsaturated fatty acids (FA) ratio and decreases the content of beneficial C18:1 cis-9, C18:1 trans-11, C18:2 cis-9,trans-11 and C18:3n-3 in milk fat. This is partly related to a lower polyunsaturated FA (PUFA) supply from ensiled forages. The aim of this thesis was to investigate the scope of increasing the content PUFA in grass and maize silages, and to establish relationships between silage quality on the one hand and the FA content and composition, post-ensiling stability of PUFA, and milk FA composition of dairy cows on the other hand. The first focus of this thesis was to quantify the variation in FA content and composition in grass (n = 101) and maize (n = 96) silages, randomly sampled from commercial dairy farms in the Netherlands, and use multivariate analysis to identify the causes of this variation. The FA content and composition of grass and maize silages were highly variable, and this variation was primarily caused by differences in plant maturity at harvest. Silages made from younger grass and maize have higher contents of C18:3n-3.Most of the variation in FA content in the ensiled forages was caused by differences in plant maturity at harvest. Changes in FA content and composition were investigated in stover (leaves and stem) and ears (cob, shank and husks) in a set of maize genotypes, grown on sandy and clay soils and harvested at 14, 42, 56, 70, and 84 days after flowering (DAF). The contents of C18:3n-3 and total FAs in the stover dry matter (DM) declined at a slow rate up to 56 DAF and then decreased rapidly during 56–84 DAF. On the other hand the content of C18:2n-6 and total FAs in the ears DM increased up to 56 DAF and thereafter remained more or less constant. The maximum amount of PUFA in silage maize can be harvested around 56 DAF. Identifying pre and post-ensiling processes that optimize the stability of PUFA was the next goal. The stability of FA were investigated in untreated and mechanically bruised perennial ryegrass (Lolium perenne L.), wilted under field conditions for 0, 12, 24, 36, and 48 h, or wilted under controlled climate conditions at three temperatures (15, 25 or 35 °C) and two light (dark or light) regimes to DM contents of 425, 525 or 625 g/kg. The oxidation of FAs during wilting of grass was mainly caused by the duration of the wilting, wilting temperature only provoked small differences, whereas mechanical bruising of grass and light intensity did not affect the changes in FA contents. The highly esterified lipids of forages are extensively hydrolysed in the silo. Therefore, the post-ensiling stability of FAs was investigated in grass and maize silages, with a wide range in qualities, exposed to air for 0, 12, and 24 h. Exposure of grass and maize silages to air results in a quantitatively small, but consistent decline in the contents of major unsaturated FAs with a concomitant increase in the proportion of C16:0. The final study evaluated the effects of feeding maize silages, ensiled at different maturities, in combination with a high or low degradable carbohydrate concentrate on nutrient intake, milk production, and composition of milk and milk fatinearly lactating dairy cows. Maize maturity at harvest at a DM content of 300-420 g/kg fresh weight, did not affect the production performance of dairy cows, but resulted in decreased contents of C18:3n-3 and total n-3 and a decreased n-6:n-3 ratio in the milk fat of dairy cows.

    Waarde van melkureum als schatter stikstofexcretie : talrijke factoren beïnvloeden relatie tussen melkureum en stikstof
    Spek, J.W. ; Bannink, A. ; Dijkstra, J. - \ 2011
    Veeteelt 28 (2011)10. - ISSN 0168-7565 - p. 40 - 41.
    melkveehouderij - melksamenstelling - ureum - stikstof - excretie - urine - ammoniak - dairy farming - milk composition - urea - nitrogen - excretion - urine - ammonia
    Het melkureum gehalte geldt in Nederland als instrument voor het schatten van de stikstofexcretie van melkvee. Wageningse onderzoekers gingen na hoe het melkureumgehalte beter gebruikt kan worden als indicator en hoe een aantal factoren verschillen in melkureumgehalte.
    Gezondheidsvoordelen van schapenmelk
    Mors, R. ter; Wit, J. de - \ 2011
    Driebergen : Louis Bolk Instituut (licatie / Louis Bolk Instituut nr. 2011-011 LbD) - 53 p.
    voeding en gezondheid - ooienmelk - melksamenstelling - gezondheidsvoedsel - voedingsstoffengehalte - schapenhouderij - voedselkwaliteit - nutrition and health - ewe milk - milk composition - health foods - nutrient content - sheep farming - food quality
    De vraag is of er een mogelijkheid is om een gezondheidsclaim te leggen op schapenmelk, zodat er meer ruimte komt voor een hogere melkprijs. Aan de hand van literatuuronderzoek is de samenstelling van schapenmelk vergeleken met de samenstelling van geiten- en koeienmelk. Vervolgens is gekeken naar de effecten op de gezondheid van de mens, van de nutriënten die meer of juist minder voorkomen in schapenmelk en is er gezocht naar wetenschappelijke onderbouwing van bekend veronderstelde voordelen van schapenmelk. Hoewel schapenmelk aanzienlijk hogere gehaltes heeft van bepaalde stoffen, zijn gezondheidsclaims niet eenvoudig te maken.
    Indicatoren om dracht te meten in melk = Biomarkers in milk to predict pregnancy in dairy cattle
    Haas, Y. de; Kruijt, L. ; Mulder, H.A. ; Smits, M.A. ; Woelders, H. - \ 2011
    Lelystad : Wageningen UR Livestock Research (Rapport / Wageningen UR Livestock Research 416)
    melkveehouderij - melkkoeien - vruchtbaarheid - melksamenstelling - melkeiwitten - indicatoren - zwangerschapsdiagnose - dairy farming - dairy cows - fertility - milk composition - milk proteins - indicators - pregnancy diagnosis
    In this project the technical possibilities were investigated to use protein profiles in dairy milk as an indicator to improve fertility.
    Zoeken naar genen voor melkvetsamenstelling : milk genomics-onderzoek vindt twee genen die een grote rol spelen in de genetische verschillen in melkvetsamenstelling
    Schennink, A. ; Visker, M.H.P.W. ; Arendonk, J.A.M. van - \ 2009
    Veeteelt 26 (2009)7. - ISSN 0168-7565 - p. 10 - 12.
    melkveehouderij - melkkoeien - melkvet - samenstelling - melksamenstelling - heritability - dierveredeling - merkers - dairy farming - dairy cows - milk fat - composition - milk composition - heritability - animal breeding - markers
    Verschillen in de samenstelling van het melkvet zijn voor een groot deel erfelijk bepaald. Twee genen spelen een grote rol in deze verschillen. Merkerinformatie kan in de toekomst gebruikt worden om te selecteren op een verbeterde samenstelling van het melkvet
    Melk nog verder verbeteren door fokkerijmaatregelen : eerste drie promoties op basis van Milk Genomics Initiative (interview met Johan van Arendonk)
    Blom, J. ; Arendonk, J.A.M. van; Stoop, W.M. ; Schennink, A. ; Heck, J. - \ 2009
    VoedingsMagazine 22 (2009)3. - ISSN 0922-8012 - p. 4 - 10.
    melksamenstelling - dierveredeling - genetische variatie - melkvetpercentage - onverzadigde vetzuren - melkeiwit - genexpressieanalyse - milk composition - animal breeding - genetic variation - milk fat percentage - unsaturated fatty acids - milk protein - genomics
    In 2004, the Milk Genomics Initiative (NGI) was launched – an exploration of the possibility to change the composition of milk though breeding measures. Five years later, it has become a fact that it is possible indeed, through selection of the most suitable animals, to attune the composition of both dairy fat and dairy protein to specific wishes. In milk fat the content of saturated fatty acids can be raised while in milk protein the casein concentration can be increased. In March and April 2009, the first three MGI research assistants obtained their doctoral degree on the basis of MGI research. An interview with the MGI project manager, Prof. Johan van Arendonk
    Feeding and grazing management for dairy cattle: opportunities for improved production
    Abrahamse, P.A. - \ 2009
    Wageningen University. Promotor(en): Seerp Tamminga, co-promotor(en): Jan Dijkstra. - [S.l. : S.n. - ISBN 9789085854548 - 158
    melkveehouderij - melkkoeien - rundveevoeding - beweidingssystemen - voeropname - melkopbrengst - melksamenstelling - melkresultaten - verbetering - begrazingsbeheer - dairy farming - dairy cows - cattle feeding - grazing systems - feed intake - milk yield - milk composition - dairy performance - improvement - grazing management
    An adequate feed intake is an important prerequisite to realize high milk production in
    dairy cows, especially during grazing. The analysis of feed intake behaviour can assist in
    understanding variation in daily intake and in improving its prediction. Indeed, our results
    indicated that differences in feed intake behaviour were more pronounced when varying
    the type of roughage than when varying the type of concentrate. Dry matter intake (DMI)
    was reduced when a ration high in grass silage was fed, but milk production was only
    numericaly affected. Grazing management might result in increased herbage intake and
    higher intake of nutrients from herbage by improved nutritional composition of herbage.
    In the first grazing experiment, herbage DMI was indeed increased when allocating cows
    daily (1Da) to a new grazing plot compared to every four days (4D) allocation, but only
    when pasture mass on offer and sward surface height (SSH) were high. Grazing time
    increased numerically and ruminating time decreased between days in the 4D treatment,
    coinciding with differences in rumen fermentation characteristics and milk composition.
    Milk yield was greater in 1Da than in 4D, but milk fatty acid (FA) composition, potentially
    influencing human health, showed hardly any difference. In a subsequent experiment,
    herbage DMI was again greater when allocating twice daily (2D) compared to once daily
    (1Db), especially when SSH was high. Grazing behaviour was more equally distributed
    in 1Db than in 2D and milk yield was increased in 2D compared to 1Db at high SSH,
    but as before milk FA composition hardly differed between treatment. The last grazing
    experiment aimed to take advantage of the higher sugar contents of grass in the afternoon
    than in the morning. It showed that grazing behaviour and herbage intake were similar
    between morning (MA) and afternoon allocation (AA), but cows receiving a fresh plot in
    the afternoon had a longer evening meal than cows receiving a fresh plot in the morning.
    This, in combination with differences in diurnal chemical composition of the grass between
    treatments probably caused higher intake of sugars in AA, resulting in a higher milk fat
    content. However, milk production remained unaffected. In conclusion, the results of
    this thesis indicate that short-term feed intake behaviour is related to DMI and therefore
    may be a helpful tool in optimizing DMI and milk production in high-production dairy
    cows. Increased pasture allocation frequency improves intake and milk yield in grazing
    dairy cows, especially when offered SSH is high enough. In intensive stripgrazing systems,
    reallocation of dairy cows following afternoon milking instead of morning milking has no
    added value.
    Ureum als instrument om eiwitvoeding te sturen nog niet betrouwbaar: Kengetal ureumgehalte beter benutten
    Spek, J.W. ; Bannink, A. ; Dijkstra, J. - \ 2009
    Veeteelt 26 (2009)6. - ISSN 0168-7565 - p. 28 - 29.
    melkveehouderij - melksamenstelling - ureum - rundveevoeding - dairy farming - milk composition - urea - cattle feeding
    Wat kunnen melkveehouders met het ureumgehalte in melk? Het kengetal zegt iets over de stikstofbenutting, maar is als instrument om de eiwitvoeding van melkkoeien te sturen nu nog onvoldoende betrouwbaar. Wageningse onderzoekers pogen daar verbetering in te brengen
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