The effect of different energy and nitrogen sources on in vitro fibre digestion and gas production kinetics of high and low quality forages.

Neethling, Kathleen Elizabeth (2016-12)

Thesis (MScAgric)--Stellenbosch University, 2016.

Thesis

ENGLISH ABSTRACT: Digestibility of fibre from the roughage component of total mixed rations for dairy cows can be influenced by the source of supplemental energy and nitrogen included in the ration. By optimizing the digestion of fibre in the rumen, dairy cows can utilize the potential nutrients in roughages to its best, and thereby obtain more substrates for optimal production. This thesis reports on two in vitro studies aimed to improve forage digestion. In the first study, a high quality forage (lucerne hay) and a poor quality forage (wheat straw) were incubated in vitro with the filter bag method with an energy source, being either maize, citrus pulp or molasses syrup and a nitrogen source, being either soybean meal, urea or no added N. The forage samples were weighed out to provide 125 mg NDF and transferred to Ankom filter bags. Bags were heat sealed and incubated in Erlenmeyer flasks for six and 30 hours at 39ºC. Energy sources were added to the incubation medium in the respective flasks and amounts were calculated to supply a metabolisable energy equivalent of 125 mg of pure starch. The amounts of the respective N sources were calculated to provide 21 mg of N per flask. Dry matter and NDF disappearance values were calculated. There was no treatment that increased DM disappearance significantly in either of the two forage sources after six or 30 hours of fermentation. The highest NDF disappearance values for LH treatments were observed in the LHCU and LHCSB treatments, after six and 30 hours, respectively. With WS as substrate, the highest NDFD values were observed in the WSCSB and WSSSB, at six and 30 hours, respectively. In the second study, the same sources were used as in the first study. Total mixed rations were simulated in which roughage was included at 229 g DM, energy sources at 188 g DM and nitrogen sources calculated to supply 21 mg N. The sample diets were incubated in sealed flasks with rumen fluid and incubation medium for 30 hours. During the incubation period, gas production was measured at regular intervals. After termination of the incubation the same digestion parameters were measured as in the first study. The highest DM disappearance was seen in LHMU and WSSSB for the two forage sources respectively. The combinations that showed the highest NDF disappearance values were M*U and S*U for lucerne hay, and S*SB for wheat straw. In both LH and WS, the highest amount of gas produced was present when M served as energy source and U as nitrogen source. It was concluded that the various combinations of forages, energy and nitrogen sources affected forage digestibility differently and knowledge thereof can be of value in formulating ruminant total mixed rations.

AFRIKAANS OPSOMMING: Verteerbaarheid van vesel uit die ruvoer komponent van totale gemengde rantsoene vir melkkoeie kan beïnvloed word deur die bron van aanvullende energie en stikstof in die rantsoen. Deur die vertering van vesel in die rumen te optimaliseer, kan melkkoeie ten volle gebruik maak van die voedingstowwe in ruvoere, om sodoende meer substrate daaruit te verkry vir optimale produksie. Hierdie tesis handel oor twee in vitro studies wat gemik was op die verbetering van vesel vertering. In die eerste studie was 'n hoë kwalitiet ruvoer (lusernhooi) en 'n swak kwaliteit ruvoer (koringstrooi) in vitro geïnkubeer deur die filtersakkie metode met òf mielies, sitrus pulp of melassestroop as energiebron en óf sojameel, ureum of die inkubasie medium as stikstofbron. Die ruvoer monsters wat 125 mg NDF bevat het is verseël in 'n filtersakkie en geïnkubeer in flesse vir ses en 30 uur teen 39ºC, tesame met die nodige hoeveelheid van die betrokke energiebron om metaboliseerbare energie gelykstaande aan 125 mg stysel te verteenwoordig, en 21 mg stikstof voorsien deur die spesifieke stikstofbron. Die verteerbaarheidsparameters; DM verdwyning en NDF verdwyning, was bepaal. Daar was geen behandeling op enige van die twee ruvoere wat aansienlik toegeneem het in DM verdwyning na ses of 30 uur van fermentasie nie. Die hoogste NDF verdwyning waardes vir LH behandelings is gesien met behandeling LHCU en LHCSB na ses en 30 uur onderskeidelik. Onder die WS behandelings was die hoogste NDFD gesien met behandeling WSCSB en WSSSB, na ses uur en 30 uur onderskeidelik. In die tweede studie is dieselfde bronne gebruik as in die eerste studie. Totale gemengde rantsoene was gesimuleer waarin ruvoer ingesluit was teen 229 g DM, energiebronne teen 188 g DM en stikstof bronne bereken tot 21 mg N. Die monsters is geïnkubeer in verseëlde flesse met rumen vloeistof en inkubasie medium vir 30 uur. Gedurende die inkubasieperiode, is gasproduksie gemeet met gereelde tussenposes. Na beëindiging van die inkubasie is dieselfde vertering parameters gemeet as in die eerste studie. Die hoogste DM verdwyning was gesien in LHMU en WSSSB vir die twee onderskeie ruvoer bronne. Die kombinasies wat die hoogste NDF verdwyning getoon het was M*U en S*U vir lusernhooi, en S*SB vir koringstrooi. In beide ruvoere was die hoogste volume gas geproduseer teenwoordig toe M gedien het as energiebron en U as stikstofbron. Daar was tot die gevolgtrekking gekom dat die verskillende kombinasies van ruvoer, energie en stikstof bronne die verteerbaarheid van vesel anders kan beinvloed. Kennis daarvan kan van groot belang wees in die formulering van totale gemengde rantsoene vir herkouers.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/100195
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