Die gebruik van die Cornell Net Carbohydrate and Protein System (CNCPS) model vir winsgewende voeding onder Suid-Afrikaanse voerkraal toestande

Van Staden, Hermanus Johannes (2002-12)

Veebedryfbestuur' -- t.p.

Thesis (MPhil)--Stellenbosch University, 2002.

Thesis

ENGLISH SUMMARY: The South African Feedlot industry develop over the past 30 years to a point where the industry today are marketing 70% of all marketed carcasses. The foundations for the feedlot industry are in the byproducts from the milling industry as well as in silage. During the past 25 years, front line scientific research increased the availability of new medicines, antibiotics, feed additives and ionofoors In the nineties a fieta-antogonist (Zilmax) with the active ingredient Zilpaterol is launched on the SA market, this product increases the ability to utilize the positive feed margin - which generally exist - for longer periods. Suspension feeds also came to the SA market during this time. At the turn of the century the feedlot industry took note of the Cornell Net Carbohydrate and Protein System (CNCPS) which was developed over the past 30 years at Cornell University in the USA. The CNCPS model consists of various components/submodels with a mechanistic understanding, which is usually needed for sustained development. The ruminal microbial population is divided into bacteria that ferment structural carbohydrate (SC) and those that ferment non-structural carbohydrate (NSC). This segregation reflects differences in N utilization and growth efficiency as well as an almost exclusive partition of energy source utilization. There is a difference in the maintenance requirements of the two groups of bacteria. Estimated passage and fermentation is central to the CNCPS model and are used to describe microbial growth. The model uses eNDF to predict rumen pH - with the acknowledgment that pH lower than 6,2 will lead to a quick decline in microbial yield. The backbone of the CNCPS model is the fermentation submodel, which also provides the composition of microbial yield. The CNCPS has a submodel that predicts rates of feedstuff degradation in the rumen, the passage of undegraded feed to the lower gut, and the amount of ME and protein that is available to the animal. In the CNCPS structural carbohydrate (SC) and nonstructural carbohydrate (NSC) are estimated from sequential NDF analyses of the feed. Data from the literature are used to predict fraction rates of SC and NSC degradation. Crude protein is partitioned into five fractions (A,C,B3,B2,B1). The amount of carbohydrate or N that is digested in the rumen is determined by the relative rates of degradation and passage. Ruminal passage rates are a function of OMI, particle size, bulk density and the type of feed that is consumed (forage vs cereal grain). The CNCPS uses equations to predict fermentation and passage of carbohydrates and protein Carbohydrates are divided into four fractions (A,B1 ,B2 an C) acording to their rate of degradation. The extended of rumen fermentation is a function of competition between fermentation and passage and do differ for different feedstuffs and particle sizes. In the CNCPS evaluations of the rations at Hurland feedlot, the following was observed: 1) Primarily there was shortages in MP- and energy allowable gain 2) eNOF was over supplied 3) Calcium (feedlime) was over supplied in all the rations 4) The low energy density of silage limits the inclusion of silage in feedlot rations 5) Shortages in peptide supply did exist - this was mainly corrected through higher levels of wheat bran inclusion and certain structural improvements were done to existing facilities to accommodate this. Some commercial feedlot data that were collected over the last 10 years are supplied. Certain seasonal tendencies are described from the data. Both AOG, intake (kg/day) and intake as a % of live mass decreases as daylight length decrease.

AFRIKAANSE OPSOMMING: Die Suid Afrikaanse Voerkraalbedryf het oor die afgelope 30 jaar ontwikkel en sodanig gegroei dat 70% van alle bemarkte karkasse vandag deur die bedryf voorsien word. Die voerkraalbedryf is hoofsaaklik geskoei op graan neweprodukte en kuilvoer. Gedurende die afgelope 25 jaar het baanbrekers wetenskaplike navorsing gelei tot die beskikbaarstelling van nuwe medikamente, antibiotikums, voeradditiewe, entstowwe en ionofore. In die negentiger jare verskyn "n Beta-agonis (Zilmax) met die aktiewe bestandeel Zilpaterol op die mark - hierdie produk maak dit by uitstek moontlik vir die voerkraal om die positiewe voermarge - wat as "n reël bestaan- vir langer periodes te benut. Suspensie voere verskyn ook vir die eerste keer gedurende die negentig's in Suid Afrika. Met die draai van die eeu is daar "n bewuswording in die Voerkraalbedryf van die Cornell Net Carbohydrate and Protein System (CNCPS) model wat gedurende die afgelope 30 jaar by die Cornell Universiteit in Amerika ontwikkel is. Hierdie model is by uitstek geskik vir die verbetering van voedingsdoeltreffendheid in vie is- en melkbeeste. Die model maak dit moontlik om nie slegs die goedkoopste dieet te formuleer nie, maar ook die winsgewendste dieet aangesien die "koste per kilogram toename" "n belangrike maatstaf vir die model is. Die CNCPS model is opgebou uit verskeie komponente/submodelle en "n meganistiese benadering word gevolg wat volhoubare ontwikkeling van die model in stand hou. Die CNCPS karakteriseer twee hoofgroepe bakterieë nl. Die SC(Strukturele Koolhidrate) en die NSC(Nie Strukturele Koolhidrate) volgens die tipe koolhidrate wat elke groep fermenteer. Hierdie verdeling reflekteer verskille in N verbruik en doeltreffendheid van groei, sowel as "n bykans eksklusiewe gebruik van energie. Dié twee groepe bakterieë se onderhoudsbehoeftes verskilook. Beraamde deurvloei- en fermentasie tempo is "n integrale deel van die CNCPS model en word gebruik om Mikrobiese groei te beskryf. Die model gebruik eNDF om die rumen pH te voorspel, met dien verstande dat "n pH laer as 6,2 lei tot "n vinnige afname in mikrobiese opbrengs. Die fermentasie submodel is die ruggraat van die CNCPS model en die samestelling van mikrobe proteïen word aangedui. Vir die beskikbaarheid van Koolhidraat en proteïen fraksies beskik die CNCPS model oor 'n submodel wat die tempo van degradasie van voedingstowwe in die rumen, sowel as die deurvloei tempo van nie gedegradeerde voer voorspel. In die CNCPS word NSC en SC koolhidrate beraam vanaf voer NDF ontledings. Data uit die literatuur word gebruik om die fraksionele tempo van SC en NSC te voorspel. Ruproteïen word verdeel in vyf fraksies verdeel nl(A,C, B3, B2, B1). Die hoeveelheid koolhidrate of N wat in die rumen verteer word, word bepaal deur relatiewe tempo's van degradasie en deurvloei. Die deurvloeitempo uit die rumen is 'n funksie van DMI, partikel grootte, digtheid en tipe voer wat gevoer word (ruvoer of kragvoer). Die CNCPS model beskik oor vergelykings wat die fermentasie en deurvloei tempo van koolhidrate en proteïen fraksies voorspel. Koolhidrate word in vier fraksies verdeel nl: (A, B1, B2 en C) - op grond van degradasie tempo. Die mate van rumenvertering is 'n funksie van kompetisie tussen vertering en uitvloei en verskil tussen voersoorte en partikelgrootte. In die evaluering van Hurland Voerkraal se rantsoene met behulp van die CNCPS model het die volgende duidelik na vore gekom: 1) Primêre tekorte het algemeen voorgekom in MP-, en energie toelaatbare groei. 2) eNDF is as 'n reëloorvoorsien en geen spysverterings steurnisse word verwag (vesel vlakke was te hoog) 3) 'n Oormaat Ca (Voerkalk) was deurgaans in alle rantsoene teenwoordig 4) Die lae energie digtheid van kuilvoer beperk die insluitingsvlakke van kuilvoer in voerkraal diëte. 5) Tekorte aan peptiede het voorgekom - wat reggestel is met die verhoging in koringsemel vlakke (Fisiese aanpassings aan bestaande strukture en metodes is gedoen om hierdie mikpunt te bereik) Ter afsluiting is data wat gedurende die afgelope tien jaar ingesamel is weergegee. Hierdie data wat gemiddelde maandelikse voerinname sowel as GOT aandui - dui op besliste seisoenale tendense wat voorkom. Beide GOT, inname in kg/dag en inname as % van liggaamsmassa daal as die dagliglengte verkort.

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