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

[摘要] ENGLISH SUMMARY: The South African Feedlot industry develop over the past 30 years to a point where theindustry today are marketing 70% of all marketed carcasses. The foundations for thefeedlot 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 newmedicines, antibiotics, feed additives and ionofoors In the nineties a fieta-antogonist(Zilmax) with the active ingredient Zilpaterol is launched on the SA market, this productincreases the ability to utilize the positive feed margin - which generally exist - forlonger 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 Carbohydrateand Protein System (CNCPS) which was developed over the past 30 years at CornellUniversity in the USA.The CNCPS model consists of various components/submodels with a mechanisticunderstanding, which is usually needed for sustained development. The ruminalmicrobial population is divided into bacteria that ferment structural carbohydrate (SC)and those that ferment non-structural carbohydrate (NSC). This segregation reflectsdifferences in N utilization and growth efficiency as well as an almost exclusive partitionof energy source utilization. There is a difference in the maintenance requirements ofthe two groups of bacteria. Estimated passage and fermentation is central to theCNCPS model and are used to describe microbial growth. The model uses eNDF topredict rumen pH - with the acknowledgment that pH lower than 6,2 will lead to a quickdecline in microbial yield.The backbone of the CNCPS model is the fermentation submodel, which also providesthe 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 proteinthat is available to the animal. In the CNCPS structural carbohydrate (SC) and nonstructuralcarbohydrate (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 therelative rates of degradation and passage. Ruminal passage rates are a function ofOMI, particle size, bulk density and the type of feed that is consumed (forage vs cerealgrain). The CNCPS uses equations to predict fermentation and passage ofcarbohydrates 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 functionof competition between fermentation and passage and do differ for different feedstuffsand 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 gain2) eNOF was over supplied3) Calcium (feedlime) was over supplied in all the rations4) The low energy density of silage limits the inclusion of silage in feedlot rations5) Shortages in peptide supply did exist - this was mainly corrected through higherlevels of wheat bran inclusion and certain structural improvements were done toexisting 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.

[发布机构] Stellenbosch University