Du Plessis, Izak (2004-04)
ENGLISH ABSTRACT: The aim of this study was to provide scientifically founded guidelines to enhance the understanding of beef production from natural pastures in arid sweet veld regions. Cattle from four breed types ranging from large to small frame sizes (Simmentaler cross > Bonsmara cross > Afrikaner > Nguni) were compared in terms of cow production and efficiency as well as the growth performance, carcass and meat quality of steers slaughtered at 18, 24 and 30 months of age. Eighteen and 30 month old steers were slaughtered at the end of the wet summer season, while the 24 month old steers were slaughtered at the end of the dry winter season. The Afrikaner herd (59.8 ± 9.0 %) had lower (p < 0.05) pregnancy rates than the Simmentaler cross (79.3 ± 12.2 %), Bonsmara cross (76.5 ± 11.1 %) and Nguni herds (86.1 ± 5.8 %). Breed differences (p < 0.05) for weaning weight and preweaning gain were observed (Simmentaler cross > Bonsmara cross > Afrikaner > Nguni). The Nguni cow herd (46.5 ± 5.7 kg/100 kg mated) was more (p < 0.05) efficient than the Simmentaler cross (36.2 ± 5.5 kg/100 kg mated), Bonsmara cross (37.7 kg/100 kg mated) and Afrikaner herds (29.5 ± 5.9 kg/100 kg mated). During the dry winter season steers gained 23.4 ± 1.5 kg from 7 to 12 months of age and from 18 to 24 months of age they gained 20.9 ± 2.0 kg. During the wet summer season steers gained 109.7 ± 1.8 kg from 12 to 18 months and 120.3 ± 4.1 kg from 24 to 30 months of age. The best (p > 0.05) fat classification codes were attained at 30 months of age and the worst (p < 0.05) at 24 months of age. Simmentaler cross steers attained the lowest (p < 0.05) fat classification at all three age classes. At 30 months of age, 15 of the 63 steers slaughtered had 3 or 4 permanent incisors, while 47 steers had 2 permanent incisors. The total amount as well as the percentage kidney and omental fat were the highest (p < 0.05) at 30 months of age and the lowest (p < 0.05) at 24 months. Back fat thickness followed the same pattern. Although breed differences for some meat quality parameters were observed, slaughter age had a much more pronounced effect on meat quality parameters. The percentage cooking loss was the lowest (p < 0.05) at 30 months of age. The meat was also darker (p > 0.05) and more red (p < 0.05) at 30 months than at 18 or 24 months of age. The pH24 was higher (p < 0.05) at 24 (5.68 ± 0.05) and 30 months (5.65 ± 0.03) than at 18 months of age (5.48 ± 0.04). A trained sensory panel only detected that Longissimus muscle samples from 18 month old steers were more tender (p < 0.05) than that from 30 month old steers. Similar results were found for Warner-Bratzler shear force values. Marketing steers at 30 months of age resulted in higher production outputs for all the breed types than marketing weaners. For marketing both weaners and 30 month old steers the Nguni herd produced more marketable kilograms live weight than the Simmentaler cross, the Bonsmara cross and the Afrikaner herds. Different marketing systems suitable to the Arid Sweet Bushveld were identified. Each marketing system is discussed in terms of its application, advantages, disadvantages and adaptability to arid regions. It is maintained throughout that a conservative approach to grazing as well as cattle management is critical to ensure stable production systems in arid regions with erratic rainfall patterns.
AFRIKAANSE OPSOMMING: Die oogmerk van hierdie studie is om wetenskaplik gefundeerde riglyne daar te stel wat die begrip van beesvleis produksie vanaf natuurlike weidings in ariede soetveld streke sal verbeter. Beeste van vier ras tipes wat wissel van groot- tot kleinraam tipes (Simmentaler kruis > Bonsmara kruis > Afrikaner > Nguni) is vergelyk in terme van koeiproduksie en effektiwiteit sowel as die groei prestasie, karkas- en vleiskwaliteit van osse op 18-, 24- en 30-maande ouderdom. Osse wat op 18 en 30 maande ouderdom geslag is, is aan die einde van die nat somerseisoen geslag, terwyl osse wat op 24 maande ouderdom geslag is, aan die einde van die droë winterseisoen geslag is. Die Afrikaner kudde (59.8 ± 9.0 %) het ’n laer (p < 0.05) reproduksietempo as die Simmentaler kruis (79.3 ± 12.2 %), Bonsmara kruis (76.5 ± 11.1 %) en die Nguni kuddes (86.1 ± 5.8 %) gehandhaaf. Ras verskille (p < 0.05) ten opsigte van speenmassas en voorspeense groeitempo’s is waargeneem (Simmentaler kruise > Bonsmara kruise > Afrikaners > Ngunis). Die Nguni koei kudde (46.5 ± 5.7 kg/100 kg gedek) was meer (p < 0.05) effektief as die Simmentalerkruis (36.2 ± 5.5 kg/100 kg gedek), Bonsmarakruis (37.7 kg/100 kg gedek) en die Afrikaner kuddes (29.5 ± 5.9 kg/100 kg gedek). Gedurende die droëwinter seisoen het die osse vanaf 7 to 12 maande ouderdom 23.4 ± 1.5 kg in liggaamsmassa toegeneem en vanaf 18 tot 24 maande ouderdom het hulle 20.9 ± 2.0 kg toegeneem. Gedurende die nat somerseisoen het die osse vanaf 12 tot 18 maande ouderdom 109.7 ± 1.8 kg in liggaamsmassa toegeneem en van 24 tot 30 maande ouderdom het hulle 120.3 ± 4.1 kg toegeneem. Die beste (p < 0.05) vetklassifikasie kodes is op 30 maande ouderdom verkry en die swakste (p < 0.05) op 24 maande ouderdom. Simmentalerkruisosse het by alle ouderdomsgroepe die swakste (P < 0.05) vetklassifikasie kodes behaal. Op 30 maande ouderdom het 15 van die 63 osse wat geslag is 3 of 4 permanente snytande gehad, terwyl 47 osse 2 permanente snytande gehad het. Die totale hoeveelheid sowel as die persentasie nier- en omentumvet was die hoogste (p < 0.05) op 30 maande ouderdom en die laagste (p < 0.05) op 24 maande ouderdom. Rugvetdikte het dieselfde patroon gevolg. Alhoewel rasverskille vir sommige vleiskwaliteitsparameters waargeneem is, het slagouderdom’n groter effek hierop. Die persentasie kookverlies was die laagste (p < 0.05) op 30 maande ouderdom. Die vleis was ook donkerder (p < 0.05) en meer rooi (p < 0.05) op 30 maande ouderdom as op 18 en 24 maande ouderdom. Die pH24 was hoër (p < 0.05) op 24 (5.68 ± 0.05) en 30 maande ouderdom (5.65 ± 0.03) as op 18 maande ouderdom (5.48 ± 0.04). Behalwe vir sagtheid, is geen ander ras- of slagouderdomsverskille in die longissimus spiermonsters vir enige van die sensoriese eienskappe wat geëvalueer is, waargeneem nie. ’n Opgeleide sensoriese paneel het slegs waargeneem dat die longissimus spiermonsters van 18 maand oue osse sagter (p < 0.05) was as dié van 30 maand oue osse. Soortgelyke resulte is vir die Warner-Bratzler snyweerstand gevind. Die bemarking van 30 maand oud osse het hoër produksie uitsette vir al die ras tipes opgelewer as die bemarking van speenkalwers. Met die bemarking van beide speenkalf en 30 maand oue osse, het die Ngunikudde meer bemarkbare kilogram lewendige massa as die Simmentalerkruis, die Bonsmarakruis en die Afrikaner kuddes geproduseer. Verskillende bemarkingstelsels wat as geskik vir die Ariede Soet Bosveld beskou word, is geïdentifiseer. Elke bemarking stelsel is in terme van sy toepassing, voor- en nadele asook die toepaslikheid daarvan in ariede streke bespreek. Dit word deurgaans aanbeveel dat ’n konserwatiewe benadering tot beide weidings- en kuddebestuur, krities is om stabiele produksiestelsels in ariede streke met wisselvalige reënvalpatrone te verseker.
Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/16314
du plessis_effect_2004.pdf (711.6Kb)
Masters Degrees (Animal Sciences)179
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