Modulation of starch digestion for productive performance in dairy cows

Shipandeni, Maria Ndakula Tautiko (2019-04)

Thesis (PhDAgric)--Stellenbosch University, 2019.


ENGLISH ABSTRACT: In this thesis, a series of experiments were conducted to ultimately investigate the effects of modulating site of starch digestion by varying ruminal fermentability of various starch sources on feed intake, production and metabolic response of transition cows. The first experiment was performed (Chapter 3) to evaluate the effects of different particle sizes on chemical composition and in vitro ruminal starch degradability of cereal grains commonly used in dairy cow diets. Four starch sources (maize 1 and 2, sorghum, barley and wheat) were ground through 1 and 2-mm screens and fractionated by sieving to obtain the following sizes: <250 (very fine), 250-500 (fine), 500-1180 (medium) and 1180-2000 μm (coarse). The generated particle size fractions and unsieved samples were separately analysed for chemical composition and fermented in vitro using rumen fluid for 0, 3, 6, 9, 12 and 24 h to determine starch degradability (Sd), and rate of starch degradation (kd), assuming a first order decay. Particle size affected (P<0.0001) the chemical composition of all grains, with the highest starch in the smallest particles and highest NDF in the largest particles. For all grains, Sd and kd increased with decreasing particle size. Results from this in vitro study suggest that starch digestion could be potentially shifted post-rumen by controlling particle size and reducing the amount fermented in the rumen. In Chapter 4 (experiment 2), we compared two mathematical approaches for determining the rate of starch degradation. The objective was to evaluate the accuracy and precision of the 7 h-kd’s by comparison with rates obtained using a non-linear first order decay model as a reference. Higher accuracy and precision were obtained by using a non-linear estimation. There is a need for using a non-linear estimation, using multiple time points or the development of alternative estimations, especially when quantifying rates of starch ddegradation for high producing cows. Experiment 3 was performed (Chapter 5) to quantify the potential of a starch binding agent (BioProtect™) to reduce in vitro rumen starch degradation of cereal grains of varying particles size. Maize and sorghum fractions used in experiment 1 were treated by spraying with BioProtect™ 24 h before in vitro fermentation to quantify starch degradability (Sd). Both treated and untreated (no BioProtect™) maize and sorghum samples were fermented in vitro. BioProtect™ was effective in decreasing starch degradability for both grains, with effects more pronounced for smaller particle sizes, by reducing Sd 17%-units compared to 7%-units for the largest particles. Simulations with the NDS software indicated that the use of BioProtect™ can reduce rumen starch digestibility, increase rumen starch escape and post rumen starch digestibility. Simulated total tract digestibility was not decreased by the use of BioProtect™ and indicated slightly reduced microbial protein production. Although BioProtect™ showed positive effects on reducing rumen starch degradation, in our simulations, larger particles were more effective at shifting the site of digestion and it could, therefore, be a more cost-effective option for our aim. Based on the in vitro results, two starch sources were selected for further in vivo investigation, to study a possible shift in the site of starch digestion. In experiment 4 (Chapter 6) the effects of starch sources and particle sizes on digesta flow, starch digestibility, ruminal fermentation parameters and production performance of dairy cows were investigated. Four ruminally-cannulated multiparous Holstein cows were used in a 4 × 4 Latin square design with a 2 x 2 factorial arrangement of treatments: maize or sorghum (M or S) either finely or coarsely ground (using a 1- or 4-mm screen sieve, F or C). Diets were formulated to contain similar starch concentration. Digesta flow was quantified using the reticular sampling technique, applying the triple-marker method. Dry matter (DM) intake, milk yield and composition were not affected by dietary treatments in exception of MUN. Milk urea nitrogen concentration was lower for cows fed maize diets: 14.36, 14.89, 16.99 and 17.09 mg/dL for MF, MC, SF and SC, respectively. Rumen pH and reticulum pH were higher for the SC diet (6.20 and 6.56, respectively) when compared to the other treatments. Rumen and reticulum pH were 5.98 and 6.33 for MF, 5.96 and 6.32 for MC, and 5.92 and 6.36 for SF, respectively. Propionate concentration was greater for both maize diets (33.21 and 32.96 vs. 31.22 and 28.68 mM; P < 0.0001) and ruminal ammonia N was lower for the fine maize diet compared to the SF and SC diets. Dietary treatments did not affect (P > 0.05) organic matter (OM) and NDF intake, nutrient flow of DM, OM and NDF, or ruminal digestibility of OM. Starch from the coarser maize was less ruminally digested (83.76 vs. 88.77% of intake) and had a greater flow to the abomasum when compared to the fine particles (1.04 vs 0.76 kg/d). However, the apparent total-tract digestibility of starch was greater in MF than MC cows (96.29 vs. 87.84%). This study confirms that coarser particles can allow part of starch digestion to be shifted from the rumen to the small intestine, but total tract starch digestibility could be decreased if ruminal digestion is not compensated postruminally. The objective of experiment 5 (Chapter 7) was to evaluate the effects of starch fermentability of diets fed during the early postpartum (PP) period on feeding behaviour, dry matter intake (DMI), lactation performance and body metabolism of fresh dairy cows. Jersey cows (n =117) were used in a randomized complete block design. Treatment diets were formulated to similar starch concentration, with ground maize (3 or 6-mm screen sieve) as the primary starch source. Treatments were fed as TMR from calving to 30 d PP before switching to a common lactation diet. Throughout the experiment DMI, milk yield and body weight were recorded daily, and milk composition, body condition score (BCS) and blood metabolites were measured weekly. Feeding coarsely ground maize (MC) increased dry matter intake (16.08 vs. 17.13 kg/d) and milk yield (20.41 vs. 21.70 kg/d) compared to finely ground maize (MF). Diet did not affect (P > 0.05) eating and rumination time and had no effects on milk composition, but milk lactose was increased in the MC compared to the MF diet (4.70 vs. 4.61%) and milk fat percentage tended to be greater (5.57 vs. 5.27%) in the MF than MC diet. Decreases in BW and BCS were greater in cows fed the MF (39.92 vs 32.24 kg and 0.23 vs. 0.14 units) than in cows fed the MC diet, resulting in increased plasma NEFA concentration (0.71 vs. 0.56 mmol/L) in MF cows. Blood glucose levels were not affected (P > 0.05). The increased DMI in cows fed the MC diets could possibly be attributed to reduced production of propionate in the rumen, resulting from shifting starch digestion postruminally and by the decreased plasma NEFA concentration. Overall, in conclusion, our results confirm that starch digestibility increases with decreasing particle size, suggesting that starch digestion could be potentially shifted post-rumen by controlling the grain particle size fed and thus reducing the amount fermented in the rumen. BioProtect™, a starch binding agent was effective in reducing in vitro rumen starch degradation, with effects more pronounced for smaller particle sizes. Shifting the site of starch digestion postruminally in early postpartum cows increased DMI, milk production and decreased mobilization of body reserves as indicated by the decreased concentration of plasma NEFA. The results of this study apparently support the hepatic oxidation theory of the control of feed intake, particularly during the early postpartum period. More processing alternatives should be investigated to reduce loss of digestibility postruminally for larger particles.

AFRIKAANSE OPSOMMING: Hierdie tesis rapporteer oor ‘n reeks eksperimente wat uitgevoer is om die invloed van die modulering van die plek van styselvertering op voerinname en produksie- en metaboliese response in oorgangskoeie te ondersoek deur die ruminale fermentasie van verskillende styselbronne te verander. Die eerste proef (Hoofstuk 3) is uitgevoer om die invloed van partikelgrootte op die chemise samestelling en in vitro ruminale styselafbraak van grane, wat tipies in melkbeesrantsoene gebruik word, na te gaan. Vier styselbronne (mielies1 en 2, sorghumgraan, hawer en koring) is deur 1 en 2 mm siwwe gemaal en gefraksioneer deur die gemaalde grane verder deur fyner siwwe te sif om die volgende partikelgroottes te verkry: <250 (baie fyn), 250-500 (fyn), 500-1180 (medium) en 1180-2000 μm (grof). Die resulterende fraksies, asook ongesifte monsters, is apart vir hul chemise samestelling ontleed en vir 0, 3, 6, 9, 12 en 24 h in vitro in gebufferde rumenvloistof gefermenteer om styseldegradeerbaarheid (Sd) en tempo van styseldegradering (kd) te bepaal, met die aanvaarding van ‘n eerste-orde afbraak. Partikelgrootte het die chemise samestelling van al die grane beïnvloed (P<0.0001) en die hoogste styselinhoud is in die fynste partikels gevind en die hoogste NDF-inhoud in die grofste partikels. Vir al die grane het Sd en kd toegeneem namate partikelgrootte afgeneem het. Resultate van hierdie in vitro-studie dui daarop dat styselvertering potensieel na die post-ruminale verteringskanaal verskuif kan word deur partikelgrootte te beheer en die hoeveelheid stysel wat in die rumen fermeteer word te verlaag. In Hoofstuk 4 (Eksperiment 2), is twee wiskundige benaderings vergelyk waarmee die tempo van styselvertering bepaal word. Die doel was om die akkuraatheid en presisie van die 7 h kd waardes te vergelyk met beramings wat verkry is met ‘n nie-lineêre eerste-ordemodel as verwysing. ’n Hoër mate van akkuraatheid en presisie is met die nie-lineêre beraming verkry. Daar bestaan ’n behoefte aan die gebruik van ‘n nie-lineêre beraming met veelvuldige tydintervalle, of die ontwikkeling van alternatiewe beramings, veral wanneer die tempo’s van styselvertering vir hoogproduserende melkkoeie gekwantifiseer word. Eksperiment 3 (Hoofstuk 5) is gedoen om die potensiaal van ‘n styselbindingsagent (BioProtect™) te kwantifiseer om in vitro styselafbraak van verskillende grane en variërende partikelgroottes te verlaag. Die mielie- en sorghumfraksies wat in Eksperiment 1 gebruik is, is 24 h voor in vitro-fermentasie met BioProtect™ behandel om styselafbraak (Sd) te kwantifiseer. Beide behandelde en onbehandelde monsters van mielies en sorghumgraan is in vitro gefermenteer. BioProtect™ was doeltreffend om styselafbraak in beide grane te verlaag en die invloed was groter met die kleiner partikels waar Sd met 17 persentasie-eenhede verlaag is in vergelyking met 7 persentasie-eenhede vir die grootste partikels. Simulasies met behulp van die NDS sagteware het aangetoon dat die gebruik van BioProtect™ ruminale styselvertering kan verlaag en terselfdertyd die ruminale verbyvloeiwaarde en post-ruminale styselvertering kan verhoog. Gesimuleerde totale-kanaal verteerbaarheid is nie deur BioProtect™ verlaag nie en het ‘n geringe verlaging in die produksie van mikrobiese proteïen aangedui. Hoewel BioProtect™ positiewe resultate getoon het om ruminale styselafbraak te verlaag, het simulasies aangedui dat groter partikels meer doeltreffend was om die plek van vertering te skuif en kan dit dus moontlik ‘n meer koste-effektiewe opsie wees om die doel van die studie te bereik. Gebaseer op die in vitro-resultate, is twee styselbronne geselekteer vir verdere in vivo-ondersoeke om die moontlike verskuiwing van die plek van styselvertering te bestudeer. In Eksperiment 4 (Hoofstuk 6) is die invloed van styselbron en partikelgrootte op die vloei van digesta, styselverteerbaarheid, ruminale fermentasieparameters en produksierespons van melkkoeie ondersoek. Vier rumengekannuleerde Holsteinkoeie is in ‘n 4 x 4 Latynse vierkantontwerp, met ‘n 2 x 2 faktoriale indeling van behandelings, gebruik: mielies of sorghum (M of S), fyn of grofgemaal (deur ‘n 1 of 4 mm sif, F of C). Diëte is geformuleer om dieselfde styselinhoud te hê. Digestavloei is gekwantifiseer deur van die retikulêre monsternemingstegniek gebruik te maak, met die toepassing van die trippelmerkermetode. Droëmateriaal (DM) inname, melkproduksie en melksamestelling is nie deur behandelings beïnvloed nie, behalwe vir MUN. Die melk-ureumstikstofinhoud was laer vir koeie op die mieliediëte: 14.36, 14.89, 16.99, en 17.09 mg/dL vir MF, MC, SF en SC, onderskeidelik. Rumen pH en retikulum pH was hoër vir die SC dieet (6.20 en 6.56, onderskeidelik) in vergelyking met die ander behandelings. Rumen- en retikulum pH was 5.98 en 6.33 vir MF, 5.96 en 6.32 vir MC en 5.92 en 6.36 vir SF, onderskeidelik. Propionaatkonsentrasies was hoër vir beide mieliediëte (33.21 en 32.96 vs. 31.22 en 28.68 mM; P < 0.0001) en rumen-ammoniak-N was laer vir die fyn mieliedieet in vergelyking met die SF en SC diëte. Dieetbehandelings het nie organiese materiaal (OM) en NDF-inname, nutriëntvloei van DM, OM en NDF, of ruminale OM-verteerbaarheid beïnvloed nie. Stysel van die grower mielies het ‘n laer rumenverteerbaarheid getoon (83.76 vs. 88.77% van inname) en het ‘n groter vloei na die abomasum gehad in vergelyking met die fyn partikels (1.04 vs. 0.76 kg/d). Die skynbare totalekanaalverteerbaarheid van stysel was egter hoër in die MF as in die MC koeie (96.29 vs. 87.84%). Hierdie studie bevestig dat growwer partikels die vermoë het om styselvertering gedeeltelik vanaf die rumen na die laer spysverteringskanaal te verskuif. Totalekanaal-styselverteerbaarheid kan egter verlaag word indien daar nie post-ruminaal vir ruminale styselvertering gekompenseer word nie. Die doel van Eksperiment 5 (Hoofstuk 7) was om die invloed van stysel-fermenteerbaarheid in vroeë-laktasiediëte vir melkkoeie op voedingsgedrag, droëmateriaalinname (DMI), melkproduksierespons en liggaamsmetabolisme na te gaan. Jerseykoeie (n = 117) is in ‘n gerandomiseerde blokontwerp gebruik. Behandelingsdiëte is geformuleer om dieselfde styselvlakke te bevat, met gemaalde mielies (3 of 6 mm sif) as die primêre styselbron. Die behandelingsdëte is in die vorm van ‘n TGR aangebied, vanaf kalwing tot 30 dae na kalwing wanneer die koeie weer teruggeplaas is op die normale laktasiedieet. Gedurende die proefperiode is melkproduksie en liggaamsmassa (LM) daagliks aangeteken, terwyl melksamestelling, liggaamskondisie (BCS) en bloedmetaboliete weekliks bepaal is. Die voeding van grofgemaalde mielies (MC) het DMI verhoog (16.08 vs. 17.13 kg/d), asook melkproduksie (20.41 vs. 21.07 kg/d) verhoog in vergelyking met fyn mielies (FM). Dieet het nie vreet- en herkoutyd beïnvloed nie, terwyl melksamestelling ook nie beïnvloed is nie, behalwe in die geval van melklaktose wat hoër was in die MC diet in vergelyking met die MF diet (4.70 vs. 4.61%) en die bottervetinhoud wat geneig het om hoër te wees in die MF diet teenoor die MC diet (5.57 vs. 5.27%). Die afname in LM en BCS was groter in koeie wat die MF dieet ontvang het as in dié op die MC dieet (39.92 vs 32.24 kg en 0.23 vs. 0.14 eenhede), wat gelei het tot verhoogde NEFA konsentrasies (0.71 vs. 0.56 mmol/L) in die MF koeie. Bloedglukosekonsentrasies is nie beïnvloed nie. Die verhoogde DMI in koeie wat die MC diëte ontvang het kan moontlik toegeskryf word aan die verlaagde propionaatproduksie in die rumen, wat die resultaat was van ‘n verskuiwing van styselvertering na die dunderm en ook as gevolg van die daling in NEFA konsentrasies. In die algemeen bevestig die huidige studieresultate dat styselvertering verhoog namate partikelgrootte afneem, wat daarop dui dat styselvertering na die laer spysverteringskanaal verskuif kan word deur die partikelgrootte van grane te beheer en sodoende die hoeveelheid stysel wat in die rumen fermenter word te verlaag. BioProtect™, ‘n styselbindingsagent, was doeltreffend om in vitro styselvertering te verlaag en die effek was groter in die geval van die kleiner partikelgroottes. Deur styselvertering in vroeëlaktasiekoeie post-ruminaal te verskuif, het die DMI en melkproduksie verhoog, terwyl die mobilisering van liggaamsreserwes verlaag het, soos aangedui deur die verlaagde plasma NEFA konsentrasies. Resultate van hierdie studie ondersteun skynbaar ook die hepatiese oksidasieteorie van voerinnamebeheer, veral gedurende die vroeë laktasieperiode. Meer prosesseringsalternatiewe behoort ondersoek te word om om die postruminale verlies van styselvertering van groter partikels te verlaag.

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