The effect of fine particle removal from ground forage samples on In Saccro dry matter and neutral detergent fiber disappearance values

Thesis (MScAgric (Animal Sciences))--University of Stellenbosch, 2011.

ENGLISH ABSTRACT: In vitro and in situ methods using the in sacco technique have a wide application in ruminant nutrition as they allow the degradability and quality of forages and ruminant diets to be determined quicker and at a lower cost than in vivo methods. These trials make use of artificial fibre bags, made of polyester (dacron) or nylon which are available in variable pore sizes. Results from such degradability trials are of great value to feed formulation programs such as AMTS.cattle and CPM Dairy and the more accurate the results are obtained from such trials the more accurate feed formulation models are enabling the ruminant nutritionist to formulate the best diet possible to reach the genetic potential of ruminants. The accepted method for in sacco trials (NRC, 2001) requires that the feed samples are ground through a 2 mm screen. This usually results in a variety of particle sizes, including a significant amount of extremely fine particles. Research has, however, shown that these fine particles can potentially be washed out of the dacron bags that are used in in sacco degradability trials. This would result in an overestimation of the soluble and rapidly fermentable nutrient fractions. The objective of this study was to determine the effect of fine particle removal from ground forage samples on the chemical composition and in vitro dry matter (DM) and neutral detergent fibre (NDF) degradability of forages. Lucerne hay, oat hay and wheat straw samples were sourced from seven different locations in the Western Cape. Samples were milled through a 2 mm screen and then sieved through either 150 μm, 125 μm or 106 μm. All fractions were analysed for DM, crude protein (CP), NDF, fat and ash. Based on the NDF content of the original samples, four samples from each forage type were selected for in vitro trials to determine DM and NDF disappearance over time. Samples were incubated for 0, 6, 24 and 48 hours in an ANKOM Daisy II incubator. Significant variation occurred within forage types in terms of chemical composition. Fine particle removal had no effect on the NDF content of lucerne hay and wheat straw, but sieved oat hay fractions had a higher NDF content than the un-sieved samples. The NDF content was on average 635.9 for the sieved OH fractions, whereas the NDF content of the un-sieved samples was 606.8. The CP content of sieved oat hay (61.4 on average) and wheat straw fractions (47.7 on average) were lower than the un-sieved fractions (65.7 for OH and 55.4 for WS), whereas for lucerne hay, sieving had no effect on CP content. Dry matter and NDF disappearances were significantly higher for the un-sieved samples than for the sieved fractions for all three forage types at all incubation times, which indicates an overestimation of the soluble and readily digestible forage fractions. Compared to sieved samples, DMD values at 0 hours (washing only) of the un-sieved samples were, on average, 13.8% higher for lucerne hay, 27.3% for oat hay and 44.7% for wheat straw. At 48 h, the overestimation of lucerne DMD for the un-sieved samples was between 4.0% (compared to 106 μm sieve) and 7.3% (compared to 150 μm sieve). This over-estimation in the un-sieved samples was carried over to all four time points. No significant differences between the fractions (150, 125 and 106) were found within a forage type at all incubation times. The estimated degradation rates and the predicted digested proportions were also significantly higher for the un-sieved fractions compared to the sieved fractions. It was concluded that fine particle removal from forage samples would result in more accurate estimations of in sacco nutrient degradability.

AFRIKAANSE OPSOMMING: In sacco in vitro- en in situ-metodes word dikwels toegepas in die studie van herkouervoeding aangesien hierdie metodes vinniger, meer effektief en meer ekonomies is as in vivo-metodes. Hierdie studies maak gebruik van kunsveselsakkies, gemaak van poliëster (dacron) of nylon wat beskikbaar is in verskeie poriegroottes. Resultate van sulke verteringsproewe is belangrik vir toepassing in voerformuleringsprogramme soos AMTS.cattle en CPM Dairy. Die resultate wat deur hierdie studies verkry word, is belangrik vir akkurate voerformulering deur formuleringsmodelle en stel die herkouervoedingkundige in staat om die ideale voer te formuleer vir die manifestering van die dier se genetiese potensieaal. Die aanvaarde in sacco-metode (NRC, 2001) vereis dat voermonsters deur ‘n 2 mm sif gemaal word wat ‘n groot verskeidenheid partikelgroottes tot gevolg het met ‘n beduidende hoeveelheid baie fyn materiaal. Navorsing het getoon dat hierdie baie fyn partikels uit die dacronsakkies gewas kan word tydens in sacco verteringstudies, met die gevolg dat die oplosbare en vinnig-verteerbare fraksie oorskat kan word. Die doel van die huidige studie was om die invloed van die verwydering van fyn partikels op die chemiese samestelling van ruvoermonsters te bepaal, asook die in vitro droë materiaal (DM) en neutraal-onoplosbaare vesel (NDF) verteerbaarheid daarvan. Monsters van lusernhooi, hawerhooi en koringstrooi, afkomstig van sewe verskillende lokaliteite in die Wes-Kaap, is deur 'n 2 mm sif gemaal en sub-monsters is deur ‘n reeks siwwe met poriegroottes van 150 μm, 125 μm of 106 μm gesif. Al die fraksies is geanaliseer vir DM, ruproteïen (RP), NDF, vet en as. Vier monsters van elke voertipe is op grond van die NDF-inhoud geselekteer vir in vitro-studies om die DM- en NDF- verteerbaarheid oor tyd te bepaal. Monsters is vir 0, 6, 24 of 48 uur geïnkubeer. Die resultate het getoon dat daar betekenisvolle variasie in chemiese samestelling binne ruvoertipes voorgekom het. Die verwydering van die fyn partikels het geen invloed die NDF-inhoud van lusernhooi en koringstrooi gehad nie. Wat hawerhooi betref, was die NDFinhoud van die gesifte monsters egter betekenisvol hoër in vergelyking met die ongesifte monsters. Die NDF inhoud was gemiddeld 635.9 vir die gesifte monsters en vir die ongesifte monsters 606.8. Sifting het geen invloed op die RP-inhoud van lusernhooi gehad nie, maar vir hawerhooi (61.4 gemiddeld) en koringstrooi (47.7 gemiddeld) was die RP-inhoud van die gesifte monsters betekenisvol laer as dié van die ongesifte monsters (65.7 vir hawerhooi en 55.4 vir koringstrooi). In vergelyking met die gesifte monsters, was die in vitro DM- en NDF-verteerbaarhede betekenisvol hoër vir die ongesifte monsters vir al drie ruvoertipes by alle inkubasietye. Hierdie resultate bevestig ‘n oorskatting van oplosbare en maklik verteerbare fraksies in gemaalde voermonsters. In vergelyking met die gesifte monsters, was die DMV-waardes van die ongesifte monsters by 0 ure (slegs gewas) gemiddeld 13.8% hoër vir lusernhooi, 27.3% vir hawerhooi en 44.7% vir koringstrooi. Na 48 h inkubasie was die oorskatting van lusern DMV vir die ongesifte monsters tussen 4.0% (vergeleke met die 106 μm sif) en 7.3% (vergeleke met 150 μm sif). Die oorskatting is oorgedra na al vier inkubasietye. Die resultate het geen noemenswaardige verskille tussen die fraksies (150 μm, 125 μm en 106 μm poriegroottes) van ‘n ruvoertipe by enige inkubasietyd aangedui nie. Die beraamde verteringstempo’s en verteerde fraksies was ook aansienlik hoër vir die ongesifte monsters in vergelyking met die gesifte monsters. Die gevolgtrekking is gemaak dat die verwydering van fyn partikels uit gemaalde ruvoermonsters die akkurate bepaling van in sacco verteerbaarheidswaardes verhoog.

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