The effect of different energy and nitrogen sources on in vitro fibre digestion of high and low quality roughages

Strauss, Mari (2015-03)

Thesis (MSc)--Stellenbosch University, 2015.

Thesis

ENGLISH SUMMARY: Fibre digestion differs among roughages and it is also affected by the supplementation of different energy and nitrogen sources. Improving ruminal fibre digestion could increase the energy intake of ruminant animals and increase production. It is thus important to maximize forage utilization. This thesis reports on two in vitro studies aimed at the improvement of DM and NDF gestibility, as well as in vitro true digestibility (IVTD). In the first study, four levels of starch were chosen (0, 35, 80 and 125 mg hexose equivalents) to supplement 125 mg of NDF from either lucerne hay (good quality roughage) or wheat straw (poor quality roughage). The in vitro procedure was a combination of the filter bag and test tube (Tilley & Terry, 1963) methods, with slight modifications to the Goering & Van Soest (1970) incubation medium. Samples were incubated at 39 °C for six or 30 hours. No significant differences were observed among levels of starch supplementation regarding fibre digestion, thus the highest inclusion level (50:50 starch HE:NDF) was used in the second study. In the second study, different combinations of energy sources (starch, sucrose, pectin) and nitrogen sources (urea, soybean meal or no N) were studied with the two roughages. The same in vitro procedure was followed as in the first study, but the treatment combinations included an incubation medium that contained no nitrogen. The same digestibility parameters were measured as in the first study and pH was also recorded at the end of the fermentations. Regarding six hours DM digestibility, lucerne showed the best results with sucrose supplementation without any N. After 30 hours, sucrose with soybean meal proved to be the best combination. For wheat straw, treatments had no effect on six hours DM disappearance, but after 30 hours, pectin and soybean meal resulted in the highest digestion values. Similar results were observed for NDF digestibility and IVTD, where the sucrose and soybean meal combination gave the best results for lucerne hay after 30 hours of incubation. For wheat straw, the highest NDF digestibly and IVTD values were observed with the pectin and soybean meal combination at 30 hours. After six hours of fermentation, the highest pH values were observed for lucerne hay with starch and urea supplementation. After 30 hours, the same combination of starch and urea resulted in the highest pH values in both roughages. In the second study, it was shown that pectin and sucrose as energy sources resulted in the highest in vitro digestibility values when supplemented to low quality (wheat straw) and high quality (lucerne hay) roughages, respectively. Soybean meal proved to be the best N supplement for both roughage sources. It was concluded that different energy sources affect in vitro digestibility of different roughages in different ways. This may have practical implications in ration formulation for ruminant animals.

AFRIKAANS OPSOMMING: Die graad van veselvertering verskil tussen ruvoere en dit word ook beïnvloed deur supplementering met verskillende energie- en stikstofbronne. Deur veselvertering te verhoog, kan herkouers meer energie inneem wat dus produksie kan verhoog. Dit is dus belangrik om veselbenutting te maksimeer. Hierdie tesis handel oor twee in vitro studies wat daarop gemik was om droëmateriaal (DM)- en NDF-vertering, asook in vitro ware verteerbaarheid (IVTD) te verhoog. In die eerste studie is vier vlakke van stysel gekies (0, 35, 80 en 125 mg heksose ekwivalente) om 125 mg NDF, afkomstig van lusern (hoë kwaliteit ruvoer) en koringstrooi (lae kwaliteit ruvoer), te supplementeer. Die in vitro-metode wat gebruik is, is ‘n kombinasie van die filtersakkiemetode en die proefbuismetode van Tilley & Terry (1963), met geringe aanpassings in die inkubasiemedium van Goering & Van Soest (1970). Monsters is vir ses of 30 ure by 39 °C geïnkubeer. Geen betekenisvolle verskille in veselvertering is waargeneem tussen die verskillende vlakke van styselsupplementering nie en daar is besluit om die hoogste insluitingsvlak (50:50 stysel:NDF) in die tweede studie te gebruik. In die tweede studie is verskillende kombinasies van energiebronne (stysel, sukrose en pektien) en stikstofbronne (ureum, sojaboon meel, of geen N) as supplemente tot die twee ruvoere nagegaan. Dieselfde in vitro-prosedure is gevolg as in die eerste studie, maar die inkubasiemedium is aangepas om geen stikstof te bevat wanneer die verskillende kombinasies getoets is nie. Dieselfde verteerbaarheidsparameters is getoets as wat die geval in die eerste studie was, terwyl pH ook na die fermentasies gemeet is. Betreffende die ses-ure fermentasies, het lusern die beste resultate getoon met sukrosesupplementering en geen stikstof nie. Na 30 ure was sukrose en sojameel die beste kombinasie. In die geval van koringstrooi, het behandelings geen invloed op ses-ure DM-verdwynings gehad nie, maar na 30 ure het pektien en sojameel die hoogste verteerbaarheidswaardes gelewer. Soortgelyke resultate is ten opsigte van NDF-verteerbaarheid en IVTD waargeneem, waar die sukrose- en sojameelkombinasie die beste resultate in lusern gelewer het na 30 ure fermentasie. In koringstrooi is die hoogste NDF-verteerbaarheid en IVTDwaardes na 30 ure waargeneem met die pektien- en sojameelkombinasie. Na ses ure fermentasie is die hoogste pH-waardes waargeneem vir lusernhooi met die supplementering van stysel en ureum. Na 30 ure het dieselfde kombinasie van stysel en ureum die hoogste pH-waardes tot gevolg gehad in beide ruvoere. In die tweede studie is bevind dat pektien en sukrose as energiebronne die hoogste in vitro-verteerbaarheidswaardes tot gevolg gehad het wanneer dit as supplemente tot, onderskeidelik, lae-kwaliteit (koringstrooi) en hoë-kwaliteit (lusernhooi) ruvoere gebruik is. Sojameel was die beste N-aanvulling vir beide ruvoerbronne. Die gevolgtrekking is gemaak dat verskillende energiebronne die in vitro-verteerbaarheid van verskillende ruvoere op verskillende maniere beïnvloed. Hierdie bevindings mag praktiese implikasies in voerformulering vir herkouers inhou.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/96643
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