Thesis (MScAgric)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: The aim of this study was to critically assess the implementation of the internal reference
method within the most recent 173 full-sibling growth trial of the Innovation Fund Abalone
Breeding Project. The trial was conducted over two locations for a period of five years, with
minimal replication for the majority of test families and a single full-sibling family was entered
into each experimental unit (basket) as an internal reference group. The primary focus was
firstly, to validate the performance of the internal reference group as a control for
comparisons and correction of environmental variation in test family performances.
Secondly, to identify areas of weakness and either make recommendations to remedy areas
of weakness or justify devoting resources to alternative methods of reducing extraneous
environmental variance with limitations on replication. The efficiency and statistical power
associated with utilising internal reference information as a covariate and for manual
correction respectively were examined for the 6 full-sibling test families that were replicated.
This study reports on the evaluation of factors which are potential sources of bias in
the internal reference method, the first of which, tag loss, was found to be significant after 6-
12 months. However, it was not found to bias internal reference group performances as the
factors which contribute to tag loss were found to act randomly. Variability in size ratio of
internal reference to test family at co-stocking proved a significant source of bias, as
reference groups smaller than their test family counterparts had reduced performances.
Testing for genotype by environment interactions was precluded due to the inherent lack of
replication and the subsequent confounding of genotype effects with inter-rearing structure
effects at one of the locations. However, significant differences were detected for both traits
of interest of the internal reference group over the two locations. Significant antagonistic
interactions were detected and identified as a source of bias for average daily weight gain of
replicate test families. The evaluation of average daily length gain for the efficiency of adjustment when the
internal reference is a covariate and the change in statistical power when the internal
reference is used for a manual correction, yielded conflicting results. The latter shows a
decrease in statistical power and the former shows an increase in efficiency, both resulting in
poor goodness of fit in the respective models. There was however evidence that when no
antagonistic interactions occurred “between replicate variance” decreased and therefore the
internal reference method has statistical merit provided all critical success factors are
satisfied.
Recommendations were made for future implementation of the internal reference
method to facilitate adequate statistical testing for sources of bias and the prevention
thereof. Additionally, an alternative method which may have merit in decreasing
environmental variance and the need for replication, is discussed. / AFRIKAANSE OPSOMMING: Die doel van die studie was om die gebruik van ʼn interne verwysingsgroep te ontleed, soos
toegepas tydens die evaluering van 173 volsib families as deel van die Innovasiefonds
Perlemoen Teelprogram. Die evaluering is gedoen op twee lokaliteite oor 'n tydperk van vyf
jaar, met minimale replikasie van die toets families en die gebruik van ‘n enkele volsib familie
as 'n interne verwysingsgroep in elke eksperimentele eenheid (mandjie). Die primêre fokus
was eerstens om die gebruik van die interne verwysingsgroep vir die korreksie van
omgewingsvariasie in die toets familie optredes te evalueer. Tweedens, om spesifieke
gebreke te identifiseer ten opsigte van die gebruik van die interne verwysingsgroep en
aanbevelings maak dit reg te stel en om die meriete van alternatiewe metodes te oorweeg.
Die doeltreffendheid en statistiese onderskeidingsvermoë van die gebruik van interne
verwysingsgroep as 'n kovariaat is ondersoek met betrekking tot die 6 volsib groepe wat oor
voldoende replikasies beskik het.
Die studie doen voorts verslag oor die evaluering van potensiële oorsake van
sydigheid ten opsigte van die gebruik van die interne verwysingsgroep, insluitend die
beduidende verlies van identifikasie vanaf 6 tot 12 maande. Geen aanduiding van sydigheid
is egter gevind en die aanleidende oorsake van verlies van identifikasie blyk van ʼn
ewekansige aard te wees. Verskille in die grootte tussen die interne verwysingsgroep en
toets-families met aanvang van evaluering blyk 'n belangrike bron van sydigheid te wees,
waar die kleiner groepering aan verminderde prestasie gekoppel word. Bepaling van
genotipe-omgewing-interaksies kon nie uitgevoer word nie as gevolg van die inherente
gebrek van replisering oor lokaliteite. Beduidende verskille is egter waargeneem tussen
interne verwysingsgroepe oor die twee lokasies ten opsigte van die beide groei eienskappe.
Beduidende antagonistiese interaksies is waargeneem en geïdentifiseer as 'n bron van
sydigheid ten opsigte van die gemiddelde daaglikse gewigstoename van replikaat
toetsfamilies.
Die evaluering van gemiddelde daaglikse lengtetoename met die interne
verwysingsgroep as is 'n kovariaat en die verandering in statistiese ontledingsvermoë tydens
die gebruik van die interne verwysingsgroep het teenstrydige resultate opgelewer.
Laasgenoemde toon 'n afname in statistiese ontledingsvermoë en die eersgenoemde toon 'n
toename in doeltreffendheid, met beide swak passing op die onderskeie modelle. In die
afwesigheid van antagonistiese interaksies tussen replikasies het variansie afgeneem en
beskik die interne verwysingsgroep oor die nodige statistiese meriete indien daar aan al die
kritiese vereistes voldoen word. Aanbevelings is gemaak ten opsigte van die toekomstige implementering van die
interne verwysingsmetode met verwysing na voldoende statistiese toetsing vir bronne van
sydigheid en die voorkoming daarvan. 'n Verdere metode wat oor die nodige meriete beskik
om die omgewingsvariasie en die noodsaaklikheid vir replikasie te verminder, word
bespreek.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/85658 |
| Date | 12 1900 |
| Creators | Difford, Gareth Frank |
| Contributors | Brink, Daniel, Stellenbosch University. Faculty of Agricultural Science. Dept. of Genetics, division of aquaculture. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Format | x, 76 p. : ill., map. |
| Rights | Stellenbosch University |
Page generated in 0.0031 seconds