Thesis (MSc)--Stellenbosch University, 2000. / ENGLISH ABSTRACT: South Africa, like many other developing countries throughout the world, has a rapidly
growing human population, resulting in a consequent increased demand for food. Ironically,
this increased food supply has to be produced on a smaller area of available agricultural land,
which means that agricultural production processes have to become more efficient.
Furthermore, the majority of the people in these countries are unschooled and poverty is a
common phenomenon. Therefore, animal scientists are faced with the challenge and the
responsibility to provide affordable, high quality food to these people.
One way of reaching this objective is to improve the utilisation of low-quality, high roughage
feedstuffs like crop residues and dry natural grass pastures. In the winter rainfall area of
South Africa alone, about 460 000 ha of wheat straw are annually available. The ruminant
animal has the ability to utilise the relatively unavailable energy (cellulose, hemi-cellulose
and pectin) in the fibre component of these low-quality forages. Unfortunately, various
factors, of which a N deficiency is the pre-dominant one, limit the utilisation of these
feedstuffs. If the ability of the ruminant to utilise low-quality, fibrous energy sources is
improved, these abundantly available and relatively inexpensive crop residues and natural
pastures can be converted into high quality protein food for human consumption. Therefore, in order to rectify the N deficiency caused by these low-quality forages, the
supplemental N requirement to optimise the fermentation and digestive processes of the
ruminant animal has to be determined. The first study was conducted to determine the
supplemental rumen degradable protein (RDP) requirement, to maximise the digestible
organic matter intake (DOMI) of Dohne Merino sheep fed wheat straw. Keeping the high
cost of natural protein supplementation in mind, the purpose of the second study was to
determine the amount of true protein that can be replaced by nonprotein nitrogen (NPN) in
RDP supplements fed to Dohne Merino sheep consuming wheat straw.
In both trials animals had ad libitum access to low-quality wheat straw (3.2% CP;
74.2% NDF) and water. In the first trial, RDP (calsium caseinate: 90% CP; 100% rumen
degradable) was intraruminally administered at 07hOOand 19hOO,at the following levels: 0,
40,80, 120 and 160 gld. Intake, fermentation and digestion were monitored to determine the
RDP requirement to maximise DOM!. Digestible organic matter (OM) intake displayed a
quadratic increase with elevated amounts of RDP (P < .01), and was maximised at an
estimated 3.15 g RDPlkg BW·75 or 11.6% of DOM. Forage OM intake tended to increase
quadratically (P = .15) with higher RDP levels. Microbial nitrogen (MN) flow to the
duodenum and microbial efficiency increased quadratically (P ~ .04) and fluid dilution rate
tended to increase in a quadratic manner (P = .15) with increased RDP supplementation
levels. Rumina! ammonia nitrogen (NH3-N) and total volatile fatty acid (VFA)
concentrations increased linearly (P ~ .07), while rumen pH exhibited a variable response to
increased RDP levels (cubic; P = .08). Increasing RDP supplementation to Dohne Merino
wethers consuming wheat straw, generally enhanced forage utilisation and DOM!.
In the second trial, urea replaced different levels of casein N on an isonitrogenous basis,
ranging from 0 - 100%. Since true protein is much more expensive than urea, the purpose of
this study was to determine the maximum natural protein level that can be replaced by urea in
RDP supplements, without adversely affecting intake and/or fermentation and digestive
processes. The control treatment provided all of the RDP in the form of calcium caseinate
(90% CP; 100% rumen degradable). The percentages of supplemental RDP from urea in the
other treatments were 25, 50, 75 and 100%. The 100% urea treatment was balanced with
maize starch to contain 40% CP and all other treatments received the same amount (150 gld)
of starch. Intake of forage OM showed a weak decreasing trend (linear; P = .16) with increasing urea levels. Ruminal digestibilities of OM and NDF were not affected (P ;;::.:18) by
urea level. Increasing urea levels resulted in linearly reduced total tract OM and NDF
digestibilities (P ~ .10). As a result, DOMI declined (linear; P < .01) with increasing
proportions of urea. Effects of increasing urea proportions on duodenal N flow, microbial
efficiency and fluid dilution rate were minimal. Ruminal NH3-N tended to increase
quadratically with increasing urea levels (P = .l4). Total VFA concentration decreased
linearly (P = .03), while rumen pH increased in a linear manner (P = .08) with increasing
urea proportions. Branched-chain volatile fatty acids (BCVFA's) and valerate decreased
linearly (P ~ .05) with increasing urea levels, while other VFA's and the acetate:propionate
ratio were generally not affected by treatment (P ;;:::.16). It appears as though ruminal and
total tract OM and NDF digestibility criteria, as well as DOMI reached maximum values at
substituting 25% of casein for urea. It is therefore concluded that replacing 25% of casein
with urea in RDP supplements, will maintain effective utilisation of low-quality forages by
sheep. / AFRIKAANSE OPSOMMING: Ontwikkelende lande, insluitend Suid-Afrika, word gekenmerk deur 'n vmmge
bevolkingsaanwas. Dit lei tot 'n verhoogde vraag na voedsel, wat op 'n gevolglik kleinerwordende
beskikbare kommersiële lanbbou-area geproduseer moet word. Die
doeltreffendheid van produksieprosesse in die landbousektor moet dus noodgedwonge
verbeter word. Die oorgrootte meerderheid van die bevolkings in ontwikkelende lande is
ongeletterd en armoede en hongersnood is soms 'n algemene verskynsel. Veekundiges word
dus gekonfronteer met die uitdaging en verantwoordelikheid om bekostigbare, hoë kwaliteit
voedsel aan hierdie mense te voorsien.
Een van die mees doeltreffende metodes om hierdie probleem aan te spreek, is om die
benutting van lae kwaliteit, hoë-vesel voerbronne, bv. oesreste en droë grasweidings te
verhoog. In die winterreënstreek van Suid-Afrika alleen, is 460 000 ha koringstrooi jaarliks
beskikbaar. Herkouers beskik oor die besondere vermoë om die relatief onbeskikbare energie
(sellulose, hemi-sellulose en pektien) in die veselkomponent van hierdie lae kwaliteit voere te
benut. Verskeie faktore, waarvan 'n N-tekort die mees prominente is, beperk egter die
benutting van hierdie voerbronne. Die uitdaging is dus om die herkouer se vermoë om
hierdie voere te benut, te optimaliseer. Sodoende word 'n geredelik beskikbare, onderbenutte
en relatief goedkoop voerbron omgeskakel in hoë kwaliteit proteïen vir menslike gebruik. Die N-aanvullingsbehoefte om die fermentasie- en verteringsprosesse van die herkouerdier te
optimaliseer moet dus bepaal word, sodat die N-tekort in herkouers, wat soortgelyke
weidings benut, reggestel kan word. Gevolglik was die doel met die eerste proef om die
behoefte aan rumen degradeerbare proteïen-(RDP)-aanvulling, vir die maksimum inname van
verteerbare organiese materiaal (VOM) van Dohne Merino skape wat koringstrooi ontvang,
te bepaal. Weens die hoë koste van natuurlike proteïenaanvulling, was die doel met die
tweede proef om die hoeveelheid ware proteïen in RDP-aanvullings, vir Dohne Merino skape
wat koringstrooi ontvang, wat met nie-proteïen stikstof (NPN) vervang kan word, te bepaal.
In beide eksperimente het die diere ad libitum toegang tot koringstrooi (3.2% RP;
74.2% NBV) en water gehad. In die eerste proefis RDP (kalsiumkaseïnaat; 90% RP; 100%
rumen degradeerbaar) teen 07hOOen 19hOOintraruminaal toegedien, teen die volgende peile:
0, 40, 80, 120 en 160 gld. Inname, fermentasie en vertering is gemonitor om die RDP
behoefte vir die maksimum inname van VOM te bepaal. Verteerbare OM-inname het 'n
stygende kwadratiese tendens (P < .01) getoon met verhoogde RDP-peile en het 'n
maksimum bereik by 'n aanvullingspeil van 3.15 g RDPlkg metaboliese liggaamsmassa
(LM·75
) of 11.6% van VOM. Organiese materiaalinname vanaf koringstrooi het geneig om
kwadraties toe te neem (P = .15) met verhoogde RDP-peile. Mikrobiese stikstof-(MN)-vloei
na die duodenum en mikrobiese effektiwiteit het kwadraties toegeneem (P :::;.;04) en vloeistof
deurvloeitempo het 'n neiging vir 'n kwadratiese toename (P = .15) met verhoogde RDPpeile
getoon. Rumen-ammoniakstikstof (NH3-N) en vlugtige vetsuur-(VVS)-konsentrasies
het lineêr toegeneem (P :::;.;07), terwyl rumen pH 'n wisselende reaksie (kubies; P = .08) met
stygende RDP-peile getoon het. Verteerbare OM-inname en benutting van koringstrooi is
verbeter deur stygende peile van RDP aanvulling by Dohne Merino hamels.
In die tweede proef is kaseïen op 'n iso-stikstof basis met verskillende ureumpeile, vanaf
o - 100%, vervang. Omdat ureum baie goedkoper is as natuurlike proteïen, was die doel van
die tweede proef om die hoeveelheid natuurlike proteïen in RDP-aanvullings te bepaal wat
met ureum vervang kan word, sonder om inname, fermentasie en vertering te benadeel. Die
kontrolebehandeling het 100% van die RDP in die vorm van kalsiumkaseïnaat (90% RP;
100% rumen degradeerbaar) voorsien, terwyl ureum in die ander behandelings onderskeidelik
25, 50, 75 en 100% van die kaseïen-N vervang het. Die 100% ureumbehandeling is met
mieliestysel tot 40% RP gebalanseer en dieselfde hoeveelheid stysel (150 gld) is by al die ander behandelings ingesluit, om moontlike effekte van stysel op rumenfermentasie te
elimineer. Organiese materiaalinname vanafkoringstrooi het 'n swak dalende tendens getoon
met stygende ureum insluitingsvlakke (lineêr; P = .16). Rumenverteerbaarheid van OM en
neutraal bestande vesel (NBV) is nie deur die ureumpeil beïnvloed nie (P ;;:: .18).
Toenemende ureumpeile het gelei tot 'n lineêre afname in totale kanaal OM en NBVverteerbaarheid
(P ~ .10). Gevolglik het VOM inname lineêr afgeneem (P < .01) met
stygende ureum insluitingspeile. Die effek van behandeling op duodenale N-vloei,
mikrobiese effektiwiteit en vloeistof deurvloeitempo was minimaal. Rumenammoniakstikstof-(
NH3-N)-konsentrasie het 'n stygende kwadratiese tendens getoon
(P = .14) met toenemende ureum peile. Totale vlugtige vetsuur-(VVS)-konsentrasies het
lineêr gedaal (P = .03), terwyl rumen pH lineêr toegeneem het (P = .08) met stygende ureum
insluitingsvlakke. Vertakte ketting VVS' e en valeriaansuurkonsentrasies het lineêr gedaal
(P ~ .05) met stygende ureumpeile, terwyl die ander VVS' e en die
asynsuur:propioonsuurverhouding oor die algemeen nie deur behandeling beïnvloed N; nie
(P ;;:: .16). Dit blyk asof VOM inname, sowel as rumen- en totale kanaal
verteerbaarheidsmaatstawwe, by 25% vervanging van kaseïen-N met ureum-N 'n maksimum
bereik het. Die gevolgtrekking is gemaak dat die doeltreffende benutting van lae kwaliteit
ruvoere deur skape, gehandhaaf sal word deur 25% van die ware proteïen in RDP-aanvullings
met ureum te vervang.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/51597 |
| Date | 12 1900 |
| Creators | Nolte, Joubert van Eeden |
| Contributors | Ferreira, A. V., Koster, H. H., Stellenbosch University. Faculty of AgriScience. Dept. of Animal Sciences. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 70 pages |
| Rights | Stellenbosch University |
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