Thesis (PhD)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: The ostrich industry is a predominantly quantitative industry; focused mainly on the production of large numbers of slaughter birds for maximum meat and leather yield. Competing in the international market in the current economic environment necessitates a more qualitative approach. Productivity and product quality are aspects that need to be improved in order to stay competitive and economically viable. Genetic parameters for ostrich slaughter traits are lacking, however, and breeding programs are yet to be developed. Data on quantitative and qualitative production and slaughter traits from a commercial ostrich breeding flock was consequently analysed to establish the relative importance of genetic and non-genetic influences on these traits. Genetic and environmental (co)variances as well as estimates of heritability, genetic and phenotypic correlations were estimated for and among the various traits using standard software for multi-trait genetic analyses.
Substantial variation, high and favourable genetic correlations as well as moderate to high heritability estimates were found among, and for distinguished body weight traits of growing ostriches. Heritability estimates of 0.14, 0.22, 0.33, 0.43 and 0.43 for 1-month, 4-month, 7-month, 10-month and 13-month-old ostrich weights were estimated in a five-trait animal model analysis.
All carcass component weight traits, with the exception of the weight of the liver, showed significant genetic variation. No significant maternal permanent environmental variance was evident for these traits. Heritability estimates ranged from 0.21 (for subcutaneous fat weight) to 0.45 (for neck weight) in multi-trait analyses. The only potentially unfavourable correlation was a high genetic correlation between live weight and subcutaneous fat weight, as fat is considered as a waste product in the present system. The heritability estimates for individual muscle weights ranged from 0.14 to 0.43, while the genetic correlation between these weights and pre-slaughter live weight were all positive, ranging from 0.59 to 0.82.
When meat quality traits were analysed it was evident that lightness (L*) and ultimate pH (pHu) showed significant genetic variation, with heritability estimates of 0.37 and 0.42, respectively. L* and pHu were negatively correlated (-0.65 ± 0.19). Since pH is an indicator of various meat quality parameters, it could be considered as an appropriate selection criterion for enhanced meat quality. With the exception of skin grading and crown length, all quantitative and qualitative skin traits showed significant genetic variation. Nodule traits were accordingly moderate to highly heritable. A negative, but favourable, correlation between weight and hair follicle score was ascertained, as hair follicles is a defect that should be selected against.
This study demonstrated that sufficient genetic variation exists for most slaughter traits to allow sustained genetic progress for these traits, should it be desired as part of the overall selection objective. Combining some of the current economically important slaughter traits in a provisional selection index, it was clear that weight and crust skin size contributed most to monetary gain (approximately 54 and 38%, respectively). It was also demonstrated with this simple index that monetary gains in slaughter bird production should be easy to achieve at all levels of production performance and data recording. / AFRIKAANSE OPSOMMING: Die volstruisbedryf is hoofsaaklik ‘n kwantitatiewe bedryf wat meerendeels fokus op die produksie van groot getalle slagvolstruise vir die produksie van vleis en leer. Siende dat die bedryf hoofsaaklik op uitvoere fokus, word aanvaar dat ‘n verandering in strategie na ‘n meer kwalitatiewe benadering nodig is, in ag geneem die huidige ekonomiese situasie en marktoestande. Produktiwiteit sowel as produkgehalte moet in ag geneem word vir die bedryf om lewensvatbaar te bly. Daar is egter ‘n gebrek aan genetiese parameters vir volstruisslageienskappe, terwyl doeltreffende teeltstelsels nog ontwikkel moet word. Data van kwantitatiewe en kwalitatiewe produksie- en slageienskappe is gevolglik van ‘n kommersiële volstruis teeltkudde verkry en ontleed om die relatiewe belang van genetiese en nie-genetiese effekte op die eienskappe te kwantifiseer. Genetiese- en omgewings (ko)variansies, asook beramings van oorerflikheid sowel as genetiese en fenotipiese korrelasies, is vervolgens vir en tussen die onderskeie eienskappe beraam deur van standaard sagteware vir veelvuldige-eienskap genetiese ontledings gebruik te maak.
Aansienlike variasie, hoë en meestal gunstige korrelasies, sowel as matige tot hoë oorerflikhede, is tussen en vir die onderskeie ligaamsgewigte van groeiende volstruise gevind. Oorerflikheidsberamings van 0.14, 0.22, 0.33, 0.43 en 0.43 is vir 1-maand, 4-maande, 7-maande, 10-maande en 13-maande-oue volstruise in ‘n vyf-eienskap dieremodel ontleding gekry.
Alle karkaskomponentgewigte, met die uitsondering van die gewig van die lewer, het betekenisvolle genetiese variasie getoon. Oorerflikheidsberamings het tussen 0.21 (vir onderhuidse vetgewig) en 0.45 (vir nekgewig) gevarieer in veelvuldige-eienskapontledings. Die enigste moontlike ongunstige korrelasie was tussen liggaamsgewig en onderhuidse vetgewig, siende dat vet as ‘n afvalproduk gereken word in die huidige stelsel. Die oorerflikhede van die gewigte van indiwiduele spiere het van 0.14 tot 0.43 gevarieer, terwyl die genetiese korrelsies tussen hierdie gewigte en voorslaggewig deurgaans positief was, met waardes wat van 0.59 tot 0.82 gewissel het.
Tydens die ontleding van vleisgehalte eienskappe was dit duidelik dat ligtheid (L*) en uiteindelike pH (pHu) genetiese variasie getoon het, met oorerflikheidsberamings van onderskeidelik 0.37 en 0.42. L* en pHu was negatief gekorreleerd op die genetiese vlak (-0.65 ± 0.19). Aangesien pH ‘n aanduiding is van verskeie vleisgehalteparameters, kan dit moontlik as ‘n indirekte seleksie-kriterium vir verbeterde vleisgehalte gesien word. Alle kwantitatiewe en kwalitatiewe veleienskappe het genetiese variasie getoon, met die uitsondering van velgradering en kroonlengte. Knoppie-eienskappe van die veerfollikels op die vel was ooreenstemmend matig tot hoog oorerflik. ‘n Negatiewe, maar gunstige, genetiese korrelasie is tussen liggaamsgewig en haarfollikelpunt beraam, siende dat haarfollikels ‘n defek is waarteen daar geselekteer moet word. Hierdie studie dui op voldoende genetiese variasie vir die meeste slageienskappe om voldoende genetiese vordering te verseker indien dit verlang sou word. Somminge van hierdie eienskappe wat tans van ekonomiese belang is, is vervolgens in ‘n voorlopige seleksie-indeks gekombineer. Dit was duidelik dat liggaamsgewig en velgrootte die meeste tot monetêre vordering bygedra het (onderskeidelik ongeveer 54 en 38%). Dit is vervolgens aangetoon dat monetêre vordering maklik haalbaar behoort te wees op alle vlakke van produksieprestasie en data-aantekening.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/80204 |
| Date | 03 1900 |
| Creators | Engelbrecht, Anel |
| Contributors | Cloete, Schalk W.P., Van Wyk, Japie B., Bunter, Kim L., Stellenbosch University. Faculty of AgriSciences. Dept. of Animal Sciences. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Detected Language | Unknown |
| Type | Thesis |
| Format | xiv, 107 p. : ill. |
| Rights | Stellenbosch University |
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