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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    Nitrate improves ammonia incorporation into rumen microbial protein in lactating dairy cows fed a low-protein diet
    Wang, Rong ; Wang, Min ; Ungerfeld, Emilio M. ; Zhang, Xiu Min ; Long, Dong Lei ; Mao, Hong Xiang ; Deng, Jin Ping ; Bannink, André ; Tan, Zhi Liang - \ 2018
    Journal of Dairy Science 101 (2018)11. - ISSN 0022-0302 - p. 9789 - 9799.
    dissolved hydrogen - microbial protein - nitrate - rumen fermentation

    Generation of ammonia from nitrate reduction is slower compared with urea hydrolysis and may be more efficiently incorporated into ruminal microbial protein. We hypothesized that nitrate supplementation could increase ammonia incorporation into microbial protein in the rumen compared with urea supplementation of a low-protein diet fed to lactating dairy cows. Eight multiparous Chinese Holstein dairy cows were used in a crossover design to investigate the effect of nitrate or an isonitrogenous urea inclusion in the basal low-protein diet on rumen fermentation, milk yield, and ruminal microbial community in dairy cows fed a low-protein diet in comparison with an isonitrogenous urea control. Eight lactating cows were blocked in 4 pairs according to days in milk, parity, and milk yield and allocated to urea (7.0 g urea/kg of dry matter of basal diet) or nitrate (14.6 g of NO3 /kg of dry matter of basal diet, supplemented as sodium nitrate) treatments, which were formulated on 75% of metabolizable protein requirements. Nitrate supplementation decreased ammonia concentration in the rumen liquids (−33.1%) and plasma (−30.6%) as well as methane emissions (−15.0%) and increased dissolved hydrogen concentration (102%), microbial N (22.8%), propionate molar percentage, milk yield, and 16S rRNA gene copies of Selenomonas ruminantium. Ruminal dissolved hydrogen was positively correlated with the molar proportion of propionate (r = 0.57), and negatively correlated with acetate-to-propionate ratio (r = −0.57) and estimated net metabolic hydrogen production relative to total VFA produced (r = −0.58). Nitrate reduction to ammonia redirected metabolic hydrogen away from methanogenesis, enhanced ammonia incorporation into rumen microbial protein, and shifted fermentation from acetate to propionate, along with increasing S. ruminantium 16S rRNA gene copies, likely leading to the increased milk yield.

    Assessing methane emission from dairy cows : modeling and experimental approaches on rumen microbial metabolism
    Lingen, Henk J. - \ 2017
    Wageningen University. Promotor(en): W.H. Hendriks, co-promotor(en): J. Dijkstra; A. Bannink; C.M. Plugge. - Wageningen : Wageningen University - ISBN 9789463431590 - 207
    dairy cows - methane - emission - microbial degradation - rumen metabolism - rumen fermentation - models - fatty acids - biochemical pathways - animal nutrition - nutrition physiology - melkkoeien - methaan - emissie - microbiële afbraak - pensmetabolisme - pensfermentatie - modellen - vetzuren - biochemische omzettingen - diervoeding - voedingsfysiologie

    Methane (CH4) is a greenhouse gas (GHG) with a global warming potential of 28 CO2 equivalents. The livestock sector was estimated to emit 7.1 gigatonnes of CO2 equivalents, which is approximately 14.5% of total global anthropogenic GHG emissions. Enteric CH4 production is the main source of GHG emissions from dairy cattle, representing 46% of the global GHG emissions in dairy supply chains. Dairy production has great value in view of the ability of ruminants to effectively turn human inedible biomass into human edible food and to produce food from non-arable land. Consequently, there is an urgent need to develop strategies to decrease dairy cattle enteric CH4 emission. Evaluation of these strategies requires meticulous quantification and increased understanding of anaerobic fermentation and methanogenesis in the rumen ecosystem. The overall aim of this PhD research was, therefore, to quantitatively evaluate enteric CH4 emission from dairy cows as affected by feeding and rumen microbial metabolism.

    A meta-analysis was performed to quantify relationships between enteric CH4 yield (per unit of feed and unit of milk) and milk FA profile in dairy cattle and to develop equations to predict CH4 yield based on milk FA profile of cows fed a wide variety of diets. Various milk FA concentrations were significantly or tended to be positively or negatively related to CH4 yield per unit of feed or milk. Mixed model multiple regression resulted in various milk FA included in optimal equations to predict CH4 yield per unit of feed and per unit of milk. These regression equations indicated a moderate potential for using milk FA profile to predict CH4 yield.

    For the development of a mechanistic model of CH4 production in the rumen, the thermodynamic control of pH2 on reaction rates of specific fermentation pathways, NADH oxidation and methanogenesis was theoretically explored. This control was determined using the thermodynamic potential factor (FT), which is a dimensionless factor that corrects a predicted kinetic reaction rate for the thermodynamic control exerted. The thermodynamic feasibility of these microbial conversions showed that the control of pH2 on individual VFA produced and associated yield of H2 and CH4 cannot be explained without considering NADH oxidation, with a considerable effect of pH.

    For obtaining experimental support of the conclusions drawn from the theoretical exploration, diurnal patterns of gaseous and dissolved metabolite concentrations in the bovine rumen, H2 and CH4 emitted, and the rumen microbiota were monitored. In addition, the effect of dietary inclusion of linseed oil on these patterns was assessed. An in vivo experiment with rumen cannulated dairy cows was performed to study the anaerobic metabolism and the microbiota composition in the rumen. A 100-fold increase in pH2 in the rumen headspace was observed at 0.5 h after feeding, followed by a decline. Qualitatively similar patterns after feeding were observed for H2 and CH4 emission, ethanol and lactate concentrations, and propionate molar proportion, whereas an opposite pattern was seen for acetate molar proportion. Associated with these patterns, a temporal biphasic change in the microbial composition was observed as based on 16S ribosomal RNA with certain taxa specifically associated with each phase. Bacterial concentrations were affected by time and increased by linseed oil supplementation. Archaeal concentrations tended to be affected by time and were not affected by diet, despite linseed oil supplementation tending to decrease the partial pressure and emission of CH4 and tending to increase propionate molar proportion. The various diurnal profiles that were monitored support the key role of the NAD+ to NADH ratio in rumen fermentation and the importance of diurnal dynamics when understanding VFA, H2 and CH4 production.

    A dynamic mechanistic model was developed, in which the thermodynamic control of pH2 on VFA fermentation pathways, and methanogenesis in the bovine rumen are incorporated. The model represents substrate degradation, microbial fermentation and methanogenesis in the rumen, with the type of VFA formed to be controlled by the NAD+ to NADH ratio, which in turn is controlled by pH2. Feed composition and feed intake rate representing a twice daily feeding regime were used as model input. The model predicted a marked peak in pH2 after feeding that rapidly declined in time. This peak in pH2 caused a decrease in NAD+ to NADH ratio followed by an increased propionate molar proportion at the expense of acetate molar proportion. In response to feeding, the model predicted a sudden increase and a steady decrease in CH4 production in time. The pattern of CH4 emission rate followed the patterns of pH2 and H2 emission rate, but its magnitude of increase in response to feeding was less pronounced. A global sensitivity analysis indicated the parameter that determines the NADH oxidation rate to explain the most substantial part of the variation of predicted daily CH4 emission. The modeling effort provides the integration of more detailed knowledge than accomplished in previous rumen fermentation models and enables assessment of diurnal dynamics of rumen metabolic pathways yielding VFA, H2 and CH4.

    For assessing the general value of the research reported in this thesis, the potential for predicting enteric CH4 emission from dairy cattle based on milk FA profile was discussed in the light of published studies and compared with empirical modeling of enteric CH4 based on feed input. Moreover, the concept of NAD-controlled fermentation was considered in a more general perspective by comparing the rumen ecosystem with bioreactor systems. Furthermore, the feasibility of the developed models as an alternative for IPCC tiered approaches was explored. In conclusion, the research reported in this thesis contributes to an increased understanding of rumen fermentation and microbial metabolism, and has provides a basis to further improve prediction models of enteric CH4 emissions from dairy cattle.

    Rumen by-pass copper = Koper voorbij de Pens
    Goselink, R.M.A. - \ 2015
    Wageningen : Wageningen UR Livestock Research (Livestock Research rapport 905) - 22
    herkauwers - koper - verteringsabsorptie - pens - pensfermentatie - spijsvertering - voedingsfysiologie - diervoeding - ruminants - copper - digestive absorption - rumen - rumen fermentation - digestion - nutrition physiology - animal nutrition
    De absorptie van koper (Cu) bij herkauwers is relatief laag vanwege de interacties tussen Cu en andere bestanddelen van het rantsoen, waardoor onoplosbare complexen gevormd worden die niet worden geabsorbeerd in de dunne darm. Dit kan mogelijk verbeterd worden door pensbestendige Cu bronnen aan te bieden, waardoor de Cu uitscheiding via de mest naar het milieu verminderd kan worden. Het doel van dit project was het evalueren van het effect van pensbestendige Cu bronnen op de Cu absorptie bij herkauwers. Dit is onderzocht met behulp van een in vitro model waarbij verschillende Cu bronnen zijn geïncubeerd om de fermentatie- en verteringsprocessen in het maagdarmkanaal te simuleren. Daarna is een proef uitgevoerd met 18 vleeskalveren waarbij twee pensbestendige Cu bronnen zijn vergeleken met kopersulfaat als controle. Het verschil in Cu absorptie tussen pensbestendige Cu bronnen en kopersulfaat was echter onvoldoende om in deze beperkte proefopzet aangetoond te kunnen worden.
    Low emission feed : opportunities to mitigate enteric methane production of dairy cows
    Hatew, B. - \ 2015
    Wageningen University. Promotor(en): Wouter Hendriks, co-promotor(en): Jan Dijkstra; Andre Bannink; Wilbert Pellikaan. - Wageningen : Wageningen University - ISBN 9789462574458 - 228
    melkkoeien - rundveevoeding - methaanproductie - milieueffect - pensfermentatie - voer - zetmeel - maïskuilvoer - graskuilvoer - diervoeding - dairy cows - cattle feeding - methane production - environmental impact - rumen fermentation - feeds - starch - maize silage - grass silage - animal nutrition

    As global demand for high-quality food originating from animal production is expected to rise due to an increasing human population and consumer income level, the expected role of ruminants in meeting this demand brings multiple challenges. Ruminant production needs to adapt to environmental changes and, at the same time, reduce its impact on the environment. Ruminants production systems have a major impact on the environment through the emission of greenhouse gases such as methane (CH4), nitrous oxide and carbon dioxide. Microbial fermentation of feeds in the gastrointestinal tract, known as enteric fermentation, is the main source of CH4 emissions from dairy production. Enteric CH4 emission is strongly related to the amount of feed fermented in the rumen, which depends on feed intake, feed composition and rumen fermentation conditions associated to the intrinsic characteristics of these feeds and the characteristics of the whole diet. Important gaps in knowledge remain however. The prime aim of this thesis was to investigate the effects of various feeding strategies to mitigate enteric CH4 emissions of dairy cows.

    First experiment was conducted to investigate the effects of type and level of starch in the concentrate. Inclusion of a high level (53%) of starch in the concentrate that accounted for 40% of the total mixed ration dry matter (DM) produced lower CH4 per unit of estimated rumen fermentable organic matter (eRFOM) than a low level (27% of DM) of starch (43.1 vs. 46.9 g/kg of eRFOM). Methane production per kg of eRFOM also was lower for diets based on rapidly fermentable starch (gelatinized maize grain) compared to diets based on slowly fermentable starch (native maize grain) (42.6 vs. 47.4 g/kg of eRFOM). However, inclusion of 53% of starch in the concentrate from both types of starch did not affect CH4 emission intensity (CH4 Ei) (CH4 emission per kg of fat- and protein-corrected milk; FPCM). In a subsequent experiment, maize silage was prepared from whole-plant maize harvested at a very early (25% DM), early (28% DM), medium (32% DM) and late (40% DM) stage of maturity and fed to dairy cows as an alternative to concentrate as starch source. Diet consisted of (on DM basis) 75% maize silage, 20% concentrate and 5% wheat straw. Increasing harvest maturity of maize silage linearly decreased CH4 yield (21.7, 23.0, 21.0 and 20.1 g/kg of DM intake) and CH4 emission as a fraction of gross energy intake (6.3, 6.7, 6.3 and 6.0%). Methane Ei tended to decrease linearly with maturity (13.0, 13.4, 13.2 and 12.1 g/kg FPCM). In another experiment grass silage as roughage source was tested. This experiment was designed to investigate the effects of N fertilisation of grassland and maturity of grass at cutting on CH4 emission in dairy cows. Two N fertilisation rates (65 vs. 150 kg of N/ha) were examined in combination with three stages of grass maturity (early, 28 days of regrowth; mid, 41 days of regrowth; and late, 62 days of regrowth). Diet contained 80:20 ratio (on DM basis) of grass silage (mainly ryegrass) and concentrate. Dry matter intake decreased with N fertilisation and maturity, and FPCM decreased with maturity but was unaffected by N fertilisation. Methane Ei (mean 15.0 g/kg of FPCM) increased by 31% and CH4 per unit digestible OM intake (mean 33.1 g/kg of DOMI) increased by 15% with increasing maturity. Methane yield (mean 23.5 g/kg of DM intake) and CH4 as a fraction of gross energy intake (mean 7%) increased by 7 and 9% with maturity, respectively, which implies an increased loss of dietary energy with progressing grass maturity. Rate of N fertilisation had no effect on CH4 Ei and CH4 yield.

    Despite the importance of in vitro gas production technique for evaluating feeds, in vitro study as a stand-alone approach was considered inadequate to fully evaluate the potential effect of feeds and rumen fermentation modifiers on CH4 production, because in vitro studies are frequently performed separately rather than in parallel with in vivo studies. To test this hypothesis, both in vitro and in vivo CH4 measurements were measured simultaneously using cows in the first experiment that were fed (and adapted to) the same dietary material used as a substrate for in vitro incubation, as donor for microbial inoculum. It was found that 24-h in vitro CH4 (mL/g of incubated organic matter) correlated well with in vivo CH4 when expressed per unit of eRFOM (R2 = 0.54), but not when expressed per unit of organic matter ingested (R2 = 0.04). In the same experiment, results showed that incubation of the same substrate with rumen inocula obtained from donor cows adapted to different diets produced a variable amount of CH4 suggesting that it is important to consider the diet of the donor animal when collecting rumen inocula for in vitro incubation. Even though the in vitro technique has limitations to represent in vivo conditions, it is useful for screening of large sets of animal feeds or feed additives to be used as a CH4 mitigation strategy. In this thesis, two in vitro experiments were conducted to examine the effects of variation in structural composition of condensed tannins (CT) in sainfoin accessions collected from across the world on CH4 production, and CT extracts obtained from a selected sainfoin accessions on CH4 production. Results revealed substantial variation among CT in their effect on in vitro CH4 production and this variation was attributed to differences in chemical structure of CT. Condensed tannins evaluated in this thesis showed to have potential to reduce in vitro CH4 production, but require further investigations to fully evaluate their in vivo effects.

    In conclusion, results from the research work conducted in this thesis show that changes in the basal diet of dairy cows and in roughage production management can substantially reduce the amount of enteric CH4 produced and thereby influence the impact of dairy production on the environment.

    What happens in the bag? : development and evaluation of a modified in situ protocol to estimate degradation of nitrogen and starch in the rumen
    Jonge, L.H. de - \ 2015
    Wageningen University. Promotor(en): Wouter Hendriks, co-promotor(en): Jan Dijkstra; H. van Laar. - Wageningen : Wageningen University - ISBN 9789462574519 - 175
    herkauwers - pensfermentatie - stikstof - zetmeelvertering - pensvertering - protocollen - evaluatie - methodologie - schatting - voedingsfysiologie - ruminants - rumen fermentation - nitrogen - starch digestion - rumen digestion - protocols - evaluation - methodology - estimation - nutrition physiology

    The most widely used method to estimate the rumen degradation of dietary components in feedstuffs is the in situ or in sacco method. This method is based on rumen incubation of substrate (feed) in nylon or dacron bags followed by rinsing and analysis of the residue. Small pores in the bag allow microbes to enter the bag whilst a variable portion of the feed is retained in the bag. The results are used to estimate the ruminal effective degradation (ED) that is used in several protein evaluation systems. The weaknesses of the in situ method are its low precision, the lack of standardization, and its inaccuracy. The accuracy can be divided in a bias with respect to the in situ method itself, and the difference between the in situ and in vivo degradation. The bias of the in situ method itself is related to several assumptions regarding the size and degradation rate of the washable fraction, secondary particle loss, and microbial contamination. The aim of this thesis was to examine possibilities to reduce this bias by modification of the in situ methodology.

    The bias related to the assumptions regarding the washout fraction was successfully reduced by developing and using a modified rinsing method that involves less vigorously shaking conditions and a solvent which mimics the rumen pH and osmolality. This modified rinsing method markedly reduced the soluble (S) fraction of N, especially for legume seeds, and the non-soluble washout (W-S) fraction, especially for starch, compared to the conventional method. Consequently, the estimation of the ED became less dependent on the assumptions regarding the degradation of the S and W-S fraction. In vitro results did not support the assumption of a much faster degradation of the W-S fraction of starch than that of the non-washout fraction of starch. The modified rinsing method also allowed measuring the in situ degradation of products that contain mainly small particles such as wheat yeast concentrates.

    The bias related to the breakdown of particles was also successfully reduced by development and application of a combination of the modified rinsing method and an in vitro method that simulates particulate matter loss during incubation. This in vitro method was based on in situ results obtained with an inert marker (i.e., silica gel) which showed that particulate matter loss during incubation was moderate and limited to particles smaller than approximately 40 μm. Correction for these losses decreased the estimated ED of feed ingredients used. This study also showed that the fractional degradation rate of starch in grains was strongly affected by the process of secondary particulate loss when using the conventional method, and applying the modified rinsing method markedly reduced the error due to secondary particulate loss.

    In comparison to the conventional method, the modified method resulted in an increase of the bias related to microbial contamination of the residues. The ratio between diaminopimelic acid (DAPA), a marker for bacterial protein, and N in the residues was higher when using the modified method than that in the conventional method. The results obtained for the modified method also indicated lysis of bacterial cells during rinsing. This bias led to a lower ED when using the modified method with the impact greatly depending on the degree of lysis of bacterial cells.

    In summary, the modified method increased the non-washout fraction of N and starch of various feed ingredients, which offers the possibility to use it for a larger range of feed ingredients, and reduced the bias related to assumptions on the washout fraction and the breakdown of particles compared to the conventional method. On the other hand, the modified method increased the bias related to microbial contamination and enlarged the difference between the in situ and in vivo degradation.

    Effects of dietary starch content and rate of fermentation on methane production in lactating dairy cows
    Hatew, B. ; Podesta, S.C. ; Laar, H. van; Pellikaan, W.F. ; St-Pierre, J.L. ; Dijkstra, J. ; Bannink, A. - \ 2015
    Journal of Dairy Science 98 (2015)1. - ISSN 0022-0302 - p. 486 - 499.
    microbial protein-synthesis - high-moisture corn - cattle fed barley - milk-production - ruminal fermentation - feed-intake - rumen fermentation - enteric methane - n balance - beet pulp
    The objective of this study was to investigate the effects of starch varying in rate of fermentation and level of inclusion in the diet in exchange for fiber on methane (CH4) production of dairy cows. Forty Holstein-Friesian lactating dairy cows of which 16 were rumen cannulated were grouped in 10 blocks of 4 cows each. Cows received diets consisting of 60% grass silage and 40% concentrate (dry matter basis). Cows within block were randomly assigned to 1 of 4 different diets composed of concentrates that varied in rate of starch fermentation [slowly (S) vs. rapidly (R) rumen fermentable; native vs. gelatinized corn grain] and level of starch (low vs. high; 270 vs. 530 g/kg of concentrate dry matter). Results of rumen in situ incubations confirmed that the fractional rate of degradation of starch was higher for R than S starch. Effective rumen degradability of organic matter was higher for high than low starch and also higher for R than S starch. Increased level of starch, but not starch fermentability, decreased dry matter intake and daily CH4 production. Milk yield (mean 24.0 ± 1.02 kg/d), milk fat content (mean 5.05 ± 0.16%), and milk protein content (mean 3.64 ± 0.05%) did not differ between diets. Methane expressed per kilogram of fat- and protein-corrected milk, per kilogram of dry matter intake, or as a fraction of gross energy intake did not differ between diets. Methane expressed per kilogram of estimated rumen-fermentable organic matter (eRFOM) was higher for S than R starch–based diets (47.4 vs. 42.6 g/kg of eRFOM) and for low than high starch–based diets (46.9 vs. 43.1 g/kg of eRFOM). Apparent total-tract digestibility of neutral detergent fiber and crude protein were not affected by diets, but starch digestibility was higher for diets based on R starch (97.2%) compared with S starch (95.5%). Both total volatile fatty acid concentration (109.2 vs. 97.5 mM) and propionate proportion (16.5 vs. 15.8 mol/100 mol) were higher for R starch– compared with S starch–based diets but unaffected by the level of starch. Total N excretion in feces plus urine and N retained were unaffected by dietary treatments, and similarly energy intake and output of energy in milk expressed per unit of metabolic body weight were not affected by treatments. In conclusion, an increased rate of starch fermentation and increased level of starch in the diet of dairy cattle reduced CH4 produced per unit of eRFOM but did not affect CH4 production per unit of feed dry matter intake or per unit of milk produced.
    Meta-analysis of relationships between enteric methane yield and milk fatty acid profile in dairy cattle
    Lingen, H.J. van; Crompton, L.A. ; Hendriks, W.H. ; Reynolds, C.K. ; Dijkstra, J. - \ 2014
    Journal of Dairy Science 97 (2014)11. - ISSN 0022-0302 - p. 7115 - 7132.
    conjugated linoleic acids - rumen fermentation - linseed oil - nutritional regulation - extruded linseed - mammary-gland - grass-silage - odd-chain - cows - energy
    Various studies have indicated a relationship between enteric methane (CH4) production and milk fatty acid (FA) profiles of dairy cattle. However, the number of studies investigating such a relationship is limited and the direct relationships reported are mainly obtained by variation in CH4 production and milk FA concentration induced by dietary lipid supplements. The aim of this study was to perform a meta-analysis to quantify relationships between CH4 yield (per unit of feed and unit of milk) and milk FA profile in dairy cattle and to develop equations to predict CH4 yield based on milk FA profile of cows fed a wide variety of diets. Data from 8 experiments encompassing 30 different dietary treatments and 146 observations were included. Yield of CH4 measured in these experiments was 21.5 ± 2.46 g/kg of dry matter intake (DMI) and 13.9 ± 2.30 g/kg of fat- and protein-corrected milk (FPCM). Correlation coefficients were chosen as effect size of the relationship between CH4 yield and individual milk FA concentration (g/100 g of FA). Average true correlation coefficients were estimated by a random-effects model. Milk FA concentrations of C6:0, C8:0, C10:0, C16:0, and C16:0-iso were significantly or tended to be positively related to CH4 yield per unit of feed. Concentrations of trans-6+7+8+9 C18:1, trans-10+11 C18:1, cis-11 C18:1, cis-12 C18:1, cis-13 C18:1, trans-16+cis-14 C18:1, and cis-9,12 C18:2 in milk fat were significantly or tended to be negatively related to CH4 yield per unit of feed. Milk FA concentrations of C10:0, C12:0, C14:0-iso, C14:0, cis-9 C14:1, C15:0, and C16:0 were significantly or tended to be positively related to CH4 yield per unit of milk. Concentrations of C4:0, C18:0, trans-10+11 C18:1, cis-9 C18:1, cis-11 C18:1, and cis-9,12 C18:2 in milk fat were significantly or tended to be negatively related to CH4 yield per unit of milk. Mixed model multiple regression and a stepwise selection procedure of milk FA based on the Bayesian information criterion to predict CH4 yield with milk FA as input (g/100 g of FA) resulted in the following prediction equations: CH4 (g/kg of DMI) = 23.39 + 9.74 × C16:0-iso - 1.06 × trans-10+11 C18:1 - 1.75 × cis-9,12 C18:2 (R2 = 0.54), and CH4 (g/kg of FPCM) = 21.13 - 1.38 × C4:0 + 8.53 × C16:0-iso - 0.22 × cis-9 C18:1 - 0.59 × trans-10+11 C18:1 (R2 = 0.47). This indicated that milk FA profile has a moderate potential for predicting CH4 yield per unit of feed and a slightly lower potential for predicting CH4 yield per unit of milk.
    Association of total mixed ration particle fractions retained on the Penn State Particle Separator with milk, fat, and protein yield lactation curves at the cow level
    Caccamo, M. ; Ferguson, J.D. ; Veerkamp, R.F. ; Schadt, I. ; Petriflieri, R. ; Azzaro, G. ; Pozzebon, A. ; Licitra, G. - \ 2014
    Journal of Dairy Science 97 (2014)4. - ISSN 0022-0302 - p. 2502 - 2511.
    physically effective fiber - neutral detergent fiber - dairy-cows - grain fermentability - rumen fermentation - midlactation cows - corn-silage - ruminal ph - size - forage
    As part of a larger project aiming to develop management evaluation tools based on results from test-day (TD) models, the objective of this study was to examine the effect of physical composition of total mixed rations (TMR) tested quarterly from March 2006 through December 2008 on milk, fat, and protein yield curves for 25 herds in Ragusa, Sicily. A random regression sire-maternal grandsire model was used to estimate variance components for milk, fat, and protein yields fitted on a full data set, including 241,153 TD records from 9,809 animals in 42 herds recorded from 1995 through 2008. The model included parity, age at calving, year at calving, and stage of pregnancy as fixed effects. Random effects were herd × test date, sire and maternal grandsire additive genetic effect, and permanent environmental effect modeled using third-order Legendre polynomials. Model fitting was carried out using ASREML. Afterward, for the 25 herds involved in the study, 9 particle size classes were defined based on the proportions of TMR particles on the top (19-mm) and middle (8-mm) screen of the Penn State Particle Separator. Subsequently, the model with estimated variance components was used to examine the influence of TMR particle size class on milk, fat, and protein yield curves. An interaction was included with the particle size class and days in milk. The effect of the TMR particle size class was modeled using a ninth-order Legendre polynomial. Lactation curves were predicted from the model while controlling for TMR chemical composition (crude protein content of 15.5%, neutral detergent fiber of 40.7%, and starch of 19.7% for all classes), to have pure estimates of particle distribution not confounded by nutrient content of TMR. We found little effect of class of particle proportions on milk yield and fat yield curves. Protein yield was greater for sieve classes with 10.4 to 17.4% of TMR particles retained on the top (19-mm) sieve. Optimal distributions different from those recommended may reflect regional differences based on climate and types and quality of forages fed.
    Cost-effectiveness of feeding strategies to reduce greenhouse gas emissions from dairy farming
    Middelaar, C.E. van; Dijkstra, J. ; Berentsen, P.B.M. ; Boer, I.J.M. de - \ 2014
    Journal of Dairy Science 97 (2014)4. - ISSN 0022-0302 - p. 2427 - 2439.
    nitrous-oxide emissions - dietary nitrate supplementation - enteric methane mitigation - special topics-mitigation - milk-production - fat supplementation - rumen fermentation - grazing behavior - linseed oil - cows
    The objective of this paper was to evaluate the cost-effectiveness of 3 feeding strategies to reduce enteric CH4 production in dairy cows by calculating the effect on labor income at the farm level and on greenhouse gas (GHG) emissions at the chain level (i.e., from production of farm inputs to the farm gate). Strategies included were (1) dietary supplementation of an extruded linseed product (56% linseed; 1 kg/cow per day in summer and 2 kg/cow per day in winter), (2) dietary supplementation of a nitrate source (75% nitrate; 1% of dry matter intake), and (3) reducing the maturity stage of grass and grass silage (grazing at 1,400 instead of 1,700 kg of dry matter/ha and harvesting at 3,000 instead of 3,500 kg of dry matter/ha). A dairy farm linear programing model was used to define an average Dutch dairy farm on sandy soil without a predefined feeding strategy (reference situation). Subsequently, 1 of the 3 feeding strategies was implemented and the model was optimized again to determine the new economically optimal farm situation. Enteric CH4 production in the reference situation and after implementing the strategies was calculated based on a mechanistic model for enteric CH4 and empirical formulas explaining the effect of fat and nitrate supplementation on enteric CH4 production. Other GHG emissions along the chain were calculated using life cycle assessment. Total GHG emissions in the reference situation added up to 840 kg of CO2 equivalents (CO2e) per t of fat- and protein-corrected milk (FPCM) and yearly labor income of €42,605. Supplementation of the extruded linseed product reduced emissions by 9 kg of CO2e/t of FPCM and labor income by €16,041; supplementation of the dietary nitrate source reduced emissions by 32 kg of CO2e/t of FPCM and labor income by €5,463; reducing the maturity stage of grass and grass silage reduced emissions by 11 kg of CO2e/t of FPCM and labor income by €463. Of the 3 strategies, reducing grass maturity was the most cost-effective (€57/t of CO2e compared with €241/t of CO2e for nitrate supplementation and €2,594/t of CO2e for linseed supplementation) and had the greatest potential to be used in practice because the additional costs were low.
    Passage of stable isotope-labeled grass silage fiber and fiber-bound protein through the gastroinstestinal tract of dairy cows
    Warner, D. ; Dijkstra, J. ; Hendriks, W.H. ; Pellikaan, W.F. - \ 2013
    Journal of Dairy Science 96 (2013)12. - ISSN 0022-0302 - p. 7904 - 7917.
    neutral detergent fiber - fresh perennial ryegrass - small-particle kinetics - in-sacco degradation - organic-matter - rumen fermentation - chemical-composition - nitrogen-fertilizer - digestion processes - physical structure
    Fractional passage rates are required to predict nutrient absorption in ruminants but data on nutrient-specific passage kinetics are largely lacking. With the use of the stable isotope ratio (d) as an internal marker, we assessed passage kinetics of fiber and fiber-bound nitrogen (N) of intrinsically labeled grass silage from fecal and omasal excretion patterns of d13C and d15N. In a 6 × 6 Latin square, lactating dairy cows received grass silages [455 g/kg of total diet dry matter (DM) ] in a 2 × 3 factorial arrangement from ryegrass swards fertilized at low (45 kg of N/ha) or high (90 kg of N/ha) levels of N and harvested at 3 maturity stages. Feed intake (16.7 ± 0.48 kg of DM/d; mean ± standard error of the mean) and milk yield (26.7 ± 0.92 kg/d) increased at the high level of N fertilization and at decreasing maturity. Nutrient digestibility decreased with increasing plant maturity, particularly at the high level of N fertilization, essentially reflecting dietary treatment effects on the nutritional composition of the grass silage. Fractional rumen passage rates (K1) were highest and total mean retention time in the gastrointestinal tract (TMRT) was lowest when based on the external marker chromium mordanted fiber (Cr-NDF; 0.047/h and 38.0 h, respectively). Fecal d13C in the acid detergent fiber fraction (13CADF) provided the lowest K1 (0.023/h) and the highest TMRT (61.1 h) and highest peak concentration time (PCT; 24.3 h) among markers. In comparison, fecal fiber-bound N (15NADF) had a considerably higher K1 (0.032/h) and lower TMRT (46.4 h) than 13CADF. Total N (measured with 15NDM) had a comparable K1 (0.034/h) to that of 15NADF but provided the highest fractional passage rates from the proximal colon-cecum (K2; 0.37/h) and lowest PCT (17.4 h) among markers. A literature review indicated unclear effects of grass silage maturity on K1 and unknown effects of N fertilization on K1. Our study indicated no effect of advancing maturity on fecal K1 and a trend for K1 to increase with the high level of N fertilization. Parameter K2 increased, whereas PCT and TMRT generally decreased with the high level of N fertilization. Omasal digesta sampling largely confirmed results based on fecal sampling. Results indicate that the use of d13C and d15N can describe fiber-specific passage kinetics of forage.
    Technical options for the mitigation of direct methane and nitrous oxide emissions from livestock: a review
    Gerber, P.J. ; Hristov, A.N. ; Henderson, B.L. ; Makkar, H.P.S. ; Oh, J. ; Lee, C. ; Meinen, R. ; Montes, F. ; Ott, T. ; Firkins, J. ; Rotz, A. ; Dell, C. ; Adesogan, A.T. ; Yang, W.Z. ; Tricarico, J.M. ; Kebreab, E. ; Waghorn, G. ; Dijkstra, J. ; Oosting, S.J. - \ 2013
    Animal 7 (2013)s2. - ISSN 1751-7311 - p. 220 - 234.
    greenhouse-gas emissions - dietary nitrate supplementation - phase compost biofilters - lactating dairy-cows - cereal grain diet - nitrification inhibitors - reduce methane - pig slurry - management options - rumen fermentation
    Although livestock production accounts for a sizeable share of global greenhouse gas emissions, numerous technical options have been identified to mitigate these emissions. In this review, a subset of these options, which have proven to be effective, are discussed. These include measures to reduce CH4 emissions from enteric fermentation by ruminants, the largest single emission source from the global livestock sector, and for reducing CH4 and N2O emissions from manure. A unique feature of this review is the high level of attention given to interactions between mitigation options and productivity. Among the feed supplement options for lowering enteric emissions, dietary lipids, nitrates and ionophores are identified as the most effective. Forage quality, feed processing and precision feeding have the best prospects among the various available feed and feed management measures. With regard to manure, dietary measures that reduce the amount of N excreted (e.g. better matching of dietary protein to animal needs), shift N excretion from urine to faeces (e.g. tannin inclusion at low levels) and reduce the amount of fermentable organic matter excreted are recommended. Among the many ‘end-of-pipe’ measures available for manure management, approaches that capture and/or process CH4 emissions during storage (e.g. anaerobic digestion, biofiltration, composting), as well as subsurface injection of manure, are among the most encouraging options flagged in this section of the review. The importance of a multiple gas perspective is critical when assessing mitigation potentials, because most of the options reviewed show strong interactions among sources of greenhouse gas (GHG) emissions. The paper reviews current knowledge on potential pollution swapping, whereby the reduction of one GHG or emission source leads to unintended increases in another
    Rumen fermentation profile and intestinal digestibility of maize and grass silages
    Ali, M. - \ 2013
    Wageningen University. Promotor(en): Wouter Hendriks, co-promotor(en): John Cone; Gert van Duinkerken. - S.l. : s.n. - ISBN 9789461736581 - 157
    melkkoeien - maïskuilvoer - graskuilvoer - pensfermentatie - verteerbaarheid - darmfysiologie - chemische samenstelling - diervoeding - voedingsfysiologie - dairy cows - maize silage - grass silage - rumen fermentation - digestibility - intestinal physiology - chemical composition - animal nutrition - nutrition physiology

    Maize and grass silages are commonly used as major feed materials for dairy cows in Europe and are becoming common parts of dairy cow rations in other parts of the world. Thenutritive value of maize and grass silages varies greatly due to variation in chemical composition. A combination of different factors such as the use of various cultivars, fertilization practices, growing conditions, harvesting technology, maturity at harvest and ensiling conditions cause this variation in chemical composition. The first aim of this thesis was to investigate relationships between the chemical composition and the in situ rumen degradation characteristics and in situ mobile nylon bag digestibility of dietary nutrients of maize and grass silages. Maize and grass silages with a broad range in chemical composition and quality parameters were selected from different Dutch commercial farms. The broad range in the chemical composition of the maize and grass silages resulted in a large variation in rumen degradable fractions of dry matter (DM), organic matter (OM), crude protein (CP), neutral detergent fibre (NDF) and starch. The intestinal digestibility of CP, NDF and/or starch was affected by the concentration of these components in the maize and grass silages, by the rumen incubation time and the rumen escape content. Regression equations were developed describing relationships between the chemical composition and the in situ ruminal and postruminal degradation characteristics of dietary nutrients of maize and grass silages. A number of the developed regression equations presented in this thesis can be used for accurate and rapid estimation of the ruminal and postruminal degradation characteristics of dietary nutrients of maize and grass silages, without conducting time consuming and expensive in situ experiments. The second aim of this thesis was to determine whether three cows are sufficient to cover the variation between individual cows in in situ rumen degradation characteristics of dietary nutrients of maize and grass silages. Significant differences (P<0.05) were found between individual cows for a number of parameters of DM, OM and CP of maize silages, indicating that four or more cows should be used for nylon bag incubations of maize silages. For grass silages, no significant differences (P>0.05) between individual cows were found for all the parameters of DM, OM, CP and NDF. The results suggest that using three cows are sufficient for nylon bag incubations of grass silages and pooling of rumen incubated residues is allowed to obtain a representative sample. The third aim of this thesis was to compare two fractionation methods; the washing machine method and a modified method, for nitrogen (N) and starch fractions of maize silages and N fractions of grass silages. The N and/or starch fractions of maize and grass silages determined, using the washing machine method (washing with water for 40 min) and the modified method (shaking with buffer solution for 60 min) were compared. The different methodological approaches of both methods resulted in different values for the washout (W), the soluble (S) and the non-washout (D+U) fractions of N of maize and grass silages and for the W, the insoluble washout (W-S) and the D+U fractions of starch of maize silages. The loss of insoluble small particles of starch was less during shaking of nylon bags in buffer solution, compared to washing nylon bags in the washing machine. Therefore, large differences were found between the D+U fractions of starch determined by both methods compared to the D+U fractions of N of maize silages. The developed regression equations for W, S and D+U fractions of N in grass silages and for D+U fractions of starch in maize silages determined by both methods can be used for rapid estimation of these fractions from chemical characteristics of maize and grass silages. The information on nutrient bioavailability of maize and grass silages presented in this thesis can be used to more accurately formulate dairy ration in terms of maintenance, health and production of dairy cows.

    Mitigation of greenhouse gases from agriculture: Role of models
    Schils, R.L.M. ; Ellis, J.L. ; Klein, C.A.M. de; Lesschen, J.P. ; Petersen, S.O. ; Sommer, S.G. - \ 2012
    Acta Agriculturae Scandinavica Section A-Animal Science 62 (2012)4. - ISSN 0906-4702 - p. 212 - 224.
    nitrous-oxide emissions - ruminant livestock systems - methane production - dairy-cows - rumen fermentation - manure management - feeding frequency - lactating cows - cattle slurry - new-zealand
    Models are widely used to simulate the emission of greenhouse gases (GHG). They help to identify knowledge gaps, estimate total emissions for inventories, develop mitigation options and policies, raise awareness and encourage adoption. These models vary in scale, scope and methodological approach. The scale increases from field, manure storage or rumen via herd or farm to country or continent. The scope may be restricted to a single GHG or include all gases. Multidisciplinary models may include nutrients, other substances or socio-economic parameters. Mechanistic process-based models have been developed from the knowledge of how GHG are produced in soils, animals and manures. These types of models often operate at the lower end of the scale, but they are also incorporated in farm and regional models. This paper discusses how the different types of models, as well as tools for farmers, are used to develop and evaluate mitigation strategies.
    Dietary nitrate supplementation reduces methane emission in beef cattle fed sugarcane-based diets
    Hulshof, R.B.A. ; Berndt, A. ; Gerrits, W.J.J. ; Dijkstra, J. ; Zijderveld, S.M. van; Newbold, J.R. ; Perdok, H.B. - \ 2012
    Journal of Animal Science 90 (2012)7. - ISSN 0021-8812 - p. 2317 - 2323.
    rumen fermentation - sheep - methanogenesis - manipulation - mitigation - livestock - nitrite - dairy - urea - wall
    The objective of this study was to determine the effect of dietary nitrate on methane emission and rumen fermentation parameters in Nellore × Guzera (Bos indicus) beef cattle fed a sugarcane based diet. The experiment was conducted with 16 steers weighing 283 ± 49 kg (mean ± SD), 6 rumen cannulated and 10 intact steers, in a cross-over design. The animals were blocked according to BW and presence or absence of rumen cannula and randomly allocated to either the nitrate diet (22 g nitrate/kg DM) or the control diet made isonitrogenous by the addition of urea. The diets consisted of freshly chopped sugarcane and concentrate (60:40 on DM basis), fed as a mixed ration. A 16-d adaptation period was used to allow the rumen microbes to adapt to dietary nitrate. Methane emission was measured using the sulfur hexafluoride tracer technique. Dry matter intake (P = 0.09) tended to be less when nitrate was present in the diet compared with the control, 6.60 and 7.05 kg/d DMI, respectively. The daily methane production was reduced (P <0.01) by 32% when steers were fed the nitrate diet (85 g/d) compared with the urea diet (125 g/d). Methane emission per kilogram DMI was 27% less (P <0.01) on the nitrate diet (13.3 g methane/kg DMI) than on the control diet (18.2 g methane/kg DMI). Methane losses as a fraction of gross energy intake (GEI) were less (P <0.01) on the nitrate diet (4.2% of GEI) than on the control diet (5.9% of GEI). Nitrate mitigated enteric methane production by 87% of the theoretical potential. The rumen fluid ammonia-nitrogen (NH3-N) concentration was significantly greater (P <0.05) for the nitrate diet. The total concentration of VFA was not affected (P = 0.61) by nitrate in the diet, while the proportion of acetic acid tended to be greater (P = 0.09), propionic acid less (P = 0.06) and acetate/propionate ratio tended to be greater (P = 0.06) for the nitrate diet. Dietary nitrate reduced enteric methane emission in beef cattle fed sugarcane based diet.
    Effects of feeding different linseed sources on omasal fatty acid flows and fatty acid profiles of plasma and milk fat in lactating dairy cows
    Sterk, A.R. ; Vlaeminck, B. ; Vuuren, A.M. van; Hendriks, W.H. ; Dijkstra, J. - \ 2012
    Journal of Dairy Science 95 (2012)6. - ISSN 0022-0302 - p. 3149 - 3165.
    conjugated linoleic acids - in-vitro - rumen fermentation - intestinal digestibility - ruminal biohydrogenation - extruded flaxseed - concentrate ratio - lipid-metabolism - sunflower oil - duodenal flow
    The aim of this experiment was to study the effects of feeding different linseed sources on omasal fatty acid (FA) flows, and plasma and milk FA profiles in dairy cows. Four ruminally cannulated lactating Holstein-Friesian cows were assigned to 4 dietary treatments in a 4 × 4 Latin square design. Dietary treatments consisted of supplementing crushed linseed (CL), extruded whole linseed (EL), formaldehyde-treated linseed oil (FL) and linseed oil in combination with marine algae rich in docosahexaenoic acid (DL). Each period in the Latin square design lasted 21 d, with the first 16 d for adaptation. Omasal flow was estimated by the omasal sampling technique using Cr-EDTA, Yb-acetate, and acid detergent lignin as digesta flow markers. The average DM intake was 20.6 ± 2.5 kg/d, C18:3n-3 intake was 341 ± 51 g/d, and milk yield was 32.0 ± 4.6 kg/d. Milk fat yield was lower for the DL treatment (0.96 kg/d) compared with the other linseed treatments (CL, 1.36 kg/d; EL, 1.49 kg/d; FL, 1.54 kg/d). Omasal flow of C18:3n-3 was higher and C18:3n-3 biohydrogenation was lower for the EL treatment (33.8 g/d; 90.9%) compared with the CL (21.8 g/d; 94.0%), FL (15.5 g/d; 95.4%), and DL (4.6 g/d; 98.5%) treatments, whereas whole-tract digestibility of crude fat was lower for the EL treatment (64.8%) compared with the CL (71.3%), FL (78.5%), and DL (80.4%) treatments. The proportion of C18:3n-3 (g/100 g of FA) was higher for the FL treatment compared with the other treatments in plasma triacylglycerols (FL, 3.60; CL, 1.22; EL, 1.35; DL, 1.12) and milk fat (FL, 3.19; CL, 0.87; EL, 0.83; DL, 0.46). Omasal flow and proportion of C18:0 in plasma and milk fat were lower, whereas omasal flow and proportions of biohydrogenation intermediates in plasma and milk fat were higher for the DL treatment compared with the other linseed treatments. The results demonstrate that feeding EL did not result in a higher C18:3n-3 proportion in plasma and milk fat despite the higher omasal C18:3n-3 flow. This was related to the decreased total-tract digestibility of crude fat. Feeding FL resulted in a higher C18:3n-3 proportion in plasma and milk fat, although the omasal C18:3n-3 flow was similar or lower than for the CL and EL treatment, respectively. Feeding DL inhibited biohydrogenation of trans-11,cis-15-C18:2 to C18:0, as indicated by the increased omasal flows and proportions of biohydrogenation intermediates in plasma and milk fat
    Effect of corn silage harvest maturity and concentrate type on milk fatty acid composition of dairy cows
    Khan, N.A. ; Tewoldebrhan, T.A. ; Zom, R.L.G. ; Cone, J.W. ; Hendriks, W.H. - \ 2012
    Journal of Dairy Science 95 (2012)3. - ISSN 0022-0302 - p. 1472 - 1483.
    conjugated linoleic acids - trans octadecenoic acid - replacing grass-silage - maize silage - rumen fermentation - detergent fiber - sunflower oil - duodenal flow - linseed oil - fish-oil
    The variation in maturity at harvest during grain filling has a major effect on the carbohydrate composition (starch:NDF ratio) and fatty acid (FA) content of corn silages, and can alter the FA composition of milk fat in dairy cows. This study evaluated the effect of silage corn (cv. Atrium) harvested and ensiled at targeted DM contents of 300, 340, 380, and 420g/kg of fresh weight and fed to dairy cows in combination with a highly degradable carbohydrate (HC) or low-degradable carbohydrate concentrate, on the nutrient intake, milk yield, and composition of milk and milk fat. Sixty-four multiparous Holstein-Friesian dairy cows in their first week of lactation were assigned to the 8 dietary treatments according to a randomized complete block design. The 8 dietary treatments consisted of a factorial combination of the 4 corn silages and the 2 concentrates. Corn silages were offered ad libitum as part of a basal forage mixture, whereas the concentrates were given at the rate of 8.5kg of DM/cow per day during the 15-wk experimental period. Dry matter, crude protein, and energy intakes did not differ across the corn silages. However, the intake of starch increased, and those of NDF and C18:3n-3 decreased with increasing maturation. Milk yield and composition were not different across the corn silages. Yield (kg/d) of milk, protein, and lactose was higher for low-degradable carbohydrate compared with HC concentrate-fed groups. Increasing maturity of corn silages decreased the content of C18:3n-3 and total n-3 and increased the n-6:n-3 ratio in milk fat. Concentrate type significantly altered the composition of all trans FA, except C18:2 trans-9,12. Inclusion of the HC concentrate in the diets increased the contents of all C18:1 trans isomers, C18:2 cis-9,trans-11, and C18:2 trans-10,cis-12 conjugated linoleic acid in milk fat. Milk fat composition was strongly influenced by the stage of lactation (wk 3 to 10). The content of all even short- and medium-chain FA changed with lactation, except C8:0 and C10:0. The content of C12:0, C14:0, and C16:0 and total saturated FA increased and the content of C18:0, C18:1 cis total, and total cis monounsaturated FA decreased with lactation. Maturity of the corn silages at harvest did not affect the production performance of dairy cows, but resulted in a decreased content of C18:3n-3, total n-3, and an increased n-6:n-3 ratio in the milk fat of dairy cows.
    Ruminal pH regulation and nutritional consequences of low pH
    Dijkstra, J. ; Ellis, J.L. ; Kebreab, E. ; Strathe, A.B. ; Lopez, S. ; France, J. ; Bannink, A. - \ 2012
    Animal Feed Science and Technology 172 (2012)1-2. - ISSN 0377-8401 - p. 22 - 33.
    volatile fatty-acids - lactating dairy-cows - resistant escherichia-coli - physically effective fiber - rumen fermentation - buffering capacity - milk-production - in-vitro - methane production - cellulolytic bacteria
    Volatile fatty acids (VFA) and lactic acid can build up in the rumen and reduce ruminal pH. Low ruminal pH for prolonged periods each day can affect feed intake, microbial metabolism and feed digestion, and has also been related to inflammation, diarrhea and milk fat depression. This paper considers aspects of pH regulation, as well as the effects of ruminal pH on rate of substrate degradation and on the profile of VFA available for absorption. Removal of VFA from the rumen by passage in the liquid phase and by absorption through the rumen wall are major processes that influence ruminal pH. The buffering capacity (BC) of rumen fluid is variable and is generally assumed to depend primarily on bicarbonate. Bicarbonate-dependent absorption is not just a primary absorption pathway of VFA but can also secrete bicarbonate at a capacity equal to that from saliva, thus removing protons from the rumen by neutralization. In addition, the inherent BC of the diet is involved in pH regulation, largely explained by the cation exchange capacity of feedstuffs. Empirical models to predict ruminal pH have had limited success. The inclusion of dietary characteristics in those models is needed to improve prediction accuracy. Representations of the effect of pH on fiber degradation adopted in models of ruminal function differ widely and include linear decline, saturation-type and sigmoidal relationships. In comparison with pH effects on degradation of fiber in sacco, most representations tend to overestimate the inhibiting effect of pH. Because the products of fiber hydrolysis are a major source of energy for microbial growth in the rumen, proper understanding and representation of fiber degradation at low pH is vital to predict microbial protein supply and VFA production satisfactorily. Variation in VFA profile is associated with variation in methane production, nutrient partitioning and milk composition. Various ruminal bacterial species have been observed to shift pathways in response to changes in pH while fermenting the same substrate. Mechanistic rumen models have adopted VFA stoichiometric coefficients related to type of substrate present in the feed or fermented in the rumen, but the majority of models do not include the effect of pH on VFA profile. In conclusion, ruminal pH is a major determinant of the profile of nutrients available for absorption. Shifting focus to factors other than salivary bicarbonate secretion will aid in better understanding ruminal pH regulation. Improved models to predict effects of ruminal pH on microbial metabolism and VFA profile will enable further optimization of dairy cow nutrition
    Persistency of methane mitigation by dietary nitrate supplementation in dairy cows
    Zijderveld, S.M. van; Gerrits, W.J.J. ; Dijkstra, J. ; Newbold, J.R. ; Hulshof, R.B.A. ; Perdok, H.B. - \ 2011
    Journal of Dairy Science 94 (2011)8. - ISSN 0022-0302 - p. 4028 - 4038.
    rumen fermentation - l-cysteine - sheep - manipulation - combination - ruminants - hydrogen - nitrite - cattle
    Feeding nitrate to dairy cows may lower ruminal methane production by competing for reducing equivalents with methanogenesis. Twenty lactating Holstein-Friesian dairy cows (33.2±6.0 kg of milk/d; 104±58 d in milk at the start of the experiment) were fed a total mixed ration (corn silage-based; forage to concentrate ratio 66:34), containing either a dietary urea or a dietary nitrate source [21 g of nitrate/kg of dry matter (DM)] during 4 successive 24-d periods, to assess the methane-mitigating potential of dietary nitrate and its persistency. The study was conducted as paired comparisons in a randomized design with repeated measurements. Cows were blocked by parity, lactation stage, and milk production at the start of the experiment. A 4-wk adaptation period allowed the rumen microbes to adapt to dietary urea and nitrate. Diets were isoenergetic and isonitrogenous. Methane production, energy balance, and diet digestibility were measured in open-circuit indirect calorimetry chambers. Cows were limit-fed during measurements. Nitrate persistently decreased methane production by 16%, whether expressed in grams per day, grams per kilogram of dry matter intake (DMI), or as percentage of gross energy intake, which was sustained for the full experimental period (mean 368 vs. 310±12.5 g/d; 19.4 vs. 16.2±0.47 g/kg of DMI; 5.9 vs.4.9±0.15% of gross energy intake for urea vs. nitrate, respectively). This decrease was smaller than the stoichiometrical methane mitigation potential of nitrate (full potential=28% methane reduction). The decreased energy loss from methane resulted in an improved conversion of dietary energy intake into metabolizable energy (57.3 vs. 58.6±0.70%, urea vs. nitrate, respectively). Despite this, milk energy output or energy retention was not affected by dietary nitrate. Nitrate did not affect milk yield or apparent digestibility of crude fat, neutral detergent fiber, and starch. Milk protein content (3.21 vs. 3.05±0.058%, urea vs. nitrate respectively) but not protein yield was lower for dietary nitrate. Hydrogen production between morning and afternoon milking was measured during the last experimental period. Cows fed nitrate emitted more hydrogen. Cows fed nitrate displayed higher blood methemoglobin levels (0.5 vs. 4.0±1.07% of hemoglobin, urea vs. nitrate respectively) and lower hemoglobin levels (7.1 vs. 6.3±0.11 mmol/L, urea vs. nitrate respectively). Dietary nitrate persistently decreased methane production from lactating dairy cows fed restricted amounts of feed, but the reduction in energy losses did not improve milk production or energy balance
    Genetic parameters for predicted methane production and potential for reducing enteric emissions through genomic selection
    Haas, Y. de; Windig, J.J. ; Calus, M.P.L. ; Dijkstra, J. ; Haan, M.H.A. de; Bannink, A. ; Veerkamp, R.F. - \ 2011
    Journal of Dairy Science 94 (2011)12. - ISSN 0022-0302 - p. 6122 - 6134.
    residual feed-intake - dairy-cows - energy-balance - milk-yield - rumen fermentation - beef-cattle - efficiency - ruminants - information - mitigation
    Mitigation of enteric methane (CH4) emission in ruminants has become an important area of research because accumulation of CH4 is linked to global warming. Nutritional and microbial opportunities to reduce CH4 emissions have been extensively researched, but little is known about using natural variation to breed animals with lower CH4 yield. Measuring CH4 emission rates directly from animals is difficult and hinders direct selection on reduced CH4 emission. However, improvements can be made through selection on associated traits (e.g., residual feed intake, RFI) or through selection on CH4 predicted from feed intake and diet composition. The objective was to establish phenotypic and genetic variation in predicted CH4 output, and to determine the potential of genetics to reduce methane emissions in dairy cattle. Experimental data were used and records on daily feed intake, weekly body weights, and weekly milk production were available from 548 heifers. Residual feed intake (MJ/d) is the difference between net energy intake and calculated net energy requirements for maintenance as a function of body weight and for fat- and protein-corrected milk production. Predicted methane emission (PME; g/d) is 6% of gross energy intake (Intergovernmental Panel on Climate Change methodology) corrected for energy content of methane (55.65 kJ/g). The estimated heritabilities for PME and RFI were 0.35 and 0.40, respectively. The positive genetic correlation between RFI and PME indicated that cows with lower RFI have lower PME (estimates ranging from 0.18 to 0.84). Hence, it is possible to decrease the methane production of a cow by selecting more-efficient cows, and the genetic variation suggests that reductions in the order of 11 to 26% in 10 yr are theoretically possible, and could be even higher in a genomic selection program. However, several uncertainties are discussed; for example, the lack of true methane measurements (and the key assumption that methane produced per unit feed is not affected by RFI level), as well as the limitations of predicting the biological consequences of selection. To overcome these limitations, an international effort is required to bring together data on feed intake and methane emissions of dairy cows.
    The effect of high-sugar grass on predicted nitrogen excretion and milk yield simulated using a dynamic model
    Ellis, J.L. ; Dijkstra, J. ; Bannink, A. ; Parsons, A.J. ; Rasmussen, S. ; Edwards, G.R. ; Kebreab, E. ; France, J. - \ 2011
    Journal of Dairy Science 94 (2011)6. - ISSN 0022-0302 - p. 3105 - 3118.
    perennial ryegrass cultivars - water-soluble carbohydrate - neutral detergent fiber - offered lolium-perenne - lactating dairy-cows - rumen fermentation - mechanistic model - digestion - cattle - diets
    High-sugar grass varieties have received considerable attention for their potential to reduce nitrogen (N) excretion and increase milk yield in cattle. However, considerable variation exists in the magnitude of response in published results. The purpose of this study is to explain the variation in response using a dynamic mechanistic model to predict observed N and milk yield results from the literature, and from simulated data. Examined effects were (1) water-soluble carbohydrate [WSC; g/kg of dry matter (DM)] increase; (2) change in crude protein (CP) and neutral detergent fiber (NDF) content of the plant with WSC increase; and (3) the level of N fertilization. The database for evaluation of model N and milk yield predictions consisted of 4 published studies with 28 treatment means for which high-sugar grasses were being evaluated. Water-soluble carbohydrate content of the diets ranged from 95 to 248 g/kg of DM, CP content ranged from 115 to 263 g/kg of DM, and the NDF content ranged from 400 to 568 g/kg of DM. Urine N, milk N, and total N excretion were predicted well by the model and followed the directional pattern of observed values within each study. Simulation results showed that the N utilization ratio increased as the WSC content of the diet increased, but to varying degrees depending on the grass scenario examined. The greatest benefit in terms of N utilization ratio and urine N levels were seen when the WSC content of grass increased at the expense of CP, followed by a 50:50 CP and NDF mix, followed by a trade for NDF. Simulated milk yield decreased slightly when WSC increased at the expense of CP, increased slightly when it increased at the expense of a CP and NDF mix, and increased most when WSC increased at the expense of NDF. Results were amplified slightly under conditions of low-N fertilization and in the absence of grain feeding. Overall, modeling is useful as an explanatory tool. The variation from results in the literature with high-WSC grass feeding may be, at least in part, the result of the level of WSC (g/kg of DM) increase, concurrent changes occurring within the CP and NDF fractions of the plant, and the plane of nutrition of the diet (grain feeding and N fertilization levels).
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