Determination of variance components for skin traits of ostriches in South Africa

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dc.contributor.advisorEngelbrecht, Anel en_ZA
dc.contributor.advisorCloete, Schalk W. P. en_ZA
dc.contributor.advisorDzama, Kennedyen_ZA
dc.contributor.advisorTada, Oberten_ZA
dc.contributor.authorNemutandani, Khetho Ratshilumela
dc.contributor.otherStellenbosch University. Faculty of AgriSciences. Dept. of Animal Science.en_ZA
dc.date.accessioned2023-03-03T08:26:21Z
dc.date.accessioned2023-05-18T07:15:56Z
dc.date.available2023-03-03T08:26:21Z
dc.date.available2023-05-18T07:15:56Z
dc.date.issued2023-03
dc.descriptionThesis (PhDAgric)--Stellenbosch University, 2023.en_ZA
dc.description.abstractENGLISH ABSTRACT: In the South African ostrich industry, production of high quality leather is a necessity for sustainability and competitiveness on the world market. However, most skins are downgraded due to poor quality, constraining enterprise revenue. The aim of this study was to identify factors contributing to skin value, to determine genetic and environmental parameters for ostrich skin traits, as well as to evaluate the performance of pure and crossbred ostriches for skin traits. Skin size (SSZ), skin grade (SG) and quill value (QV) were assessed as predictors of skin value, using multiple regression techniques. Pearson’s correlations among independent variables confirmed that SG was the dominant driver of skin value, as indicated by a high negative correlation (r=-0.88) with skin income. Skin traits such as nodule size score (NSZ), nodule shape score (NS), hair follicle score (HF) and pitting score (PIT) mostly failed to reflect the variation in skin value accounted for by QV and SG, respectively. Single-trait heritability estimates, derived on South African Black (SAB) birds, for skin traits such as SSZ, skin weight (SW) and skin thickness (ST) were 0.37±0.06, 0.27±0.06 and 0.20±0.05, respectively. Overall, direct heritability ranged from low (0.08) for pitting scores to high (0.42) for hair follicle scores. Genetic correlations of slaughter weight (SLW) with SSZ, SW and ST were 0.92, 0.48, and 0.15. A positive genetic correlation of 0.33 was found between SLW and NSZ. A high genetic correlation of 0.71 existed between scores for NS and NSZ. For threshold traits, heritability estimates ranged from 0.17 for nodule direction (NDIR) to 0.47 for nodule outliers (OUTL) in the 5- trait threshold model analysis for non-linear and binomial traits. In the 6-trait linear- threshold analysis including SSZ as a linear trait, heritability estimates ranged from 0.20 for NDISTR to 0.39 for OUTL. For both sets of analyses, significant genetic correlations were found between OUTL and PIT (respectively 0.49 and 0.71). Evaluation of purebreds showed that Zimbabwean Blue (ZB) and Kenyan Red (KR) birds outperformed their SAB contemporaries for most size-related traits (P<0.05). Heterosis were found for SLW, SSZ, and NSZ, for SAB and ZB as well as for SAB and KR combinations. The effect of the taller KR dam line was significant for SLW, neckline total length, neckline crown length and neckline width in the middle. However, most of the size dependent genetic group effects were reduced or removed when farm weight was modelled as a covariate across analyses. High scores for HF were observed for all the crosses though. It was concluded that: 1. Skin grading was the dominant force in determining skin value; 2. Genetic variation existed and exploitable levels of variation were found in most quantitative skin characteristics; therefore genetic progress appear feasible through selection; 3. Genetic progress can also be achieved for traits not conforming to the assumptions of normality; 4. ZB and KR birds performed better for size-related traits than their SAB contemporaries, indicating that commercial crossbreeding could improve slaughter weight and size-related traits in hybrids. Overall, this study provides information to the ostrich industry regarding options for the exploitation of additive genetic gains, the choice of breeds, as well as crossbreeding options. This information will provide a sound foundation for genetic improvement of skin traits that is based on scientific principles.en_ZA
dc.description.abstractAFRIKAANSE OPSOMMING: Die produksie van goeie kwaliteit leer is noodsaaklik vir die Suid-Afrikaanse volstruisbedryf om volhoubaar en kompeterend te bly in die wêreldmark. Die oorgrote meerderheid van volstruisvelle word egter afgegradeer weens swak kwaliteit, wat die winsgewindheid van volstruisproduksie negatief beïnvloed. Die doel van hierdie studie was gevolglik om faktore te identifiseer wat velinkomste bepaal, om genetiese en omgewingsparameters vir volstruis veleienskappe te beraam, asook om die veleienskappe van suiwer rasse en kruiskombinasies te vergelyk. Velgrootte, velgradering en knoppie-aanvaarbaarheid as voorspellers van velwaarde is met behulp van meervoudige regressiemetodes ondersoek. Daar is aangetoon dat velgradering die dominante dryfveer van velprys was, soos bevestig deur die hoë negatiewe Pearson korrelasie (r=-0.88) tussen hierdie veranderlikes. Veleienskappe wat op ‘n linieêre skaal gepunt is, soos knoppiegrootte (KG), knoppievorm (KV), haarfollikels (HF) en putjieskade (PS) kon nie die variasie in velprys verklaar wat onderskeidelik aan knoppie-aanvaarbaarheid en velgradering toegeskryf kon word nie. Oorerflikheid vir veleienskappe, soos gemeet by Suid-Afrikaanse Swart (SAS) volstruise, het gewissel van laag (0.08) vir die voorkoms van putjieskade, tot hoog (0.42) vir die voorkoms van haarfollikels. Genetiese korrelasies van slaggewig (SG) met velgrootte, slaggewig en veldikte was 0.92, 0.48, en 0.15, onderskeidelik. ‘n Positiewe genetiese korrelasie van 0.33 is ook tussen slaggewig en knoppiegroottepunt gevind. Daar was ook ‘n hoë positiewe genetiese korrelasie van 0.71 tussen knoppievormpunt en knoppiegroottepunt. Oorerflikheidsberamings vir drumpel eienskappe het gewissel van 0.17 vir knoppierigting tot 0.47 vir uitskietknoppies in ‘n 5-eienskap ontleding vir nie-lineêre en binominale eienskappe. In ‘n 6-eienskap ontleding wat velgrootte as lineêre eienskap ingesluit het, het oorerflikhede gevarieer van 0.20 vir knoppieverspreiding tot 0.39 vir uitskietknoppies. In beide ontledings is betekenisvolle genetiese korrelasies tussen die voorkoms van uitskietknoppies en putjieskade (0.49 en 0.71, onderskeidelik) gevind. Die vergelyking tussen suiwer volstruisrasse het bevind dat Zimbabwiese Blou (ZB) en Keniaanse Rooi (KR) volstruise beter gevaar het as die SAS volstruise vir meeste grootte- verwante veleienskappe (P<0.05). Heterose is gevind vir verskeie eienskappe, o.a. slaggewig, velgrootte en knoppiegrootte, vir kruisings tussen SAS en ZB, en tussen SAS en KR volstruise, onderskeidelik. Die effek van die groter KR wyfie lyn was betekenisvol vir slaggewig, totale neklynlengte, neklynkroonlengte en neklynbreedte in die middel van die vel. Meeste van die grootte-afhanklike effekte het egter verdwyn of verminder toe lewende gewig as ‘n kovariant ingesluit is in die ontledings. Hoë punte vir haarfollikels was egter merkbaar by al die kruisvolstruise van KR-oorsprong. Die gevolgtrekkings van die studie was dus: 1. Velgradering is die dominante faktor wat velinkomste bepaal; 2. Genoegsame genetiese variasie bestaan vir meeste kwantitatiewe veleienskappe; genetiese vordering behoort dus moontlik te wees met seleksie; 3. Genetiese vordering kan ook gemaak word in veleienskappe wat nie normaal versprei is nie; 4. Zimbabwiese Blou en Keniaanse Rooi volstruise het beter gevaar as die Suid-Afrikaanse Swart volstruise vir eienskappe wat verwant is aan grootte, wat aandui dat kommersiële kruisteling slaggewig en ander grootte-verwante eienskappe kan verbeter in kruisvolstruise. Die studie verskaf inligting wat deur die volstruisbedryf gebruik kan word vir besluitneming rondom opsies vir genetiese verbetering, raskeuse en kruisteling. Die bevindinge kan as ‘n goeie basis dien vir genetiese verbetering gebaseer op wetenskaplike beginsels.af_ZA
dc.description.versionDoctoralen_ZA
dc.format.extentiii, 119 pages : illustrations (some color), mapsen_ZA
dc.identifier.urihttp://hdl.handle.net/10019.1/127320
dc.language.isoen_ZAen_ZA
dc.publisherStellenbosch : Stellenbosch Universityen_ZA
dc.rights.holderStellenbosch Universityen_ZA
dc.subject.lcshOstrich products industry -- South Africa -- Environmental aspects en_ZA
dc.subject.lcshOstriches en_ZA
dc.subject.lcshOstrich feathersen_ZA
dc.subject.lcshOstrich leather -- Quality en_ZA
dc.subject.lcshOstriches -- Economic aspects -- South Africaen_ZA
dc.subject.lcshOstrich skin en_ZA
dc.subject.lcshVarianceen_ZA
dc.subject.lcshGenetic engineeringen_ZA
dc.subject.nameUCTDen_ZA
dc.titleDetermination of variance components for skin traits of ostriches in South Africaen_ZA
dc.typeThesisen_ZA
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