Thesis (MScAgric )--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: The main object of this study was to estimate heritabilities and possible genetic correlations for and
between reproductive traits in a composite multi breed beef cattle herd. Reproduction is a complex
process with many components. Due to the nature of the data, obtained from the two farms of the
Johannesburg Metropolitan Council from 1974 to 1993, only calving date (CD), calving date with a
penalty score (CDP), calving success (CS), calving interval (CI), age at first calving (AFC), longevity
and stayability at 36, 48, 60, 72 and 84 months were investigated.
A GFCAT set of programmes was used and fitted on a sire model to analyse all the categorical traits.
Heritabilities and product moment correlations between predicted breeding values for stayability at
36, 48, 60, 72, 84 months, calving success (CS) and longevity, were estimated. The estimated
heritabilities on the underlying scale for these traits were 0.06, 0.10, 0.06, 0.03, 0.11, 0.03 and 0.08,
respectively. Product moment correlations between breeding values for stayability traits were very
low. The highest correlation of 0.22 was obtained between 36 and 48 months. Heritability estimates
and correlations between traits appear to be of such a low magnitude that selection for these
characteristics would result in limited improvement and indicate that the sire had little influence on his
daughter's stayability, longevity and CS.
For the analyses oflinear traits (CI, CD, CDP and AFC), a REML procedure fitting a multitrait animal
model (using REML VCE 4.2.5 package of Groeneveld, 1998) was used. Heritabilities and geneticcorrelations for and between calving interval (CI), calving date (CD), calving date with a penalty
score (CDP) and age at first calving (AFC) were estimated as traits of the dam. The estimated
heritabilities for CI, CD, CDP and AFC obtained in this study were 0.01, 0.04, 0.06 and 0.40,
respectively with a repeatability of 0.07, 0.12 and 0.13 for CI, CD and CDP, respectively. Genetic
correlations between traits obtained varied from low to moderate, except for the high correlations
between CD and CDP (0.98), CI and CD (0.75) and CI and CDP (0.79). Heritabilities, genetic
correlations and repeatabilities of CD and CDP obtained in this study suggest that CD and CDP are
the same traits and that selection for CDP rather than for CD does not have any additional advantage.
Due to the additional advantages of CD over CI and the fact that CD is a less biased measurement of
the female reproductive complex, CD appears to be of genetic value and should.be considered-as a
possible selection criterion to ensure genetic improvement for reproduction in a beef cattle herd. / AFRIKAANSE OPSOMMING: Die doeI met hierdie studie was om oorerflikhede vir en moontlike genetiese korrelasies tussen
verskillende reproduksiekenmerke in 'n meerras vleisbeeskudde te bepaal. Reproduksie is 'n
komplekse proses en bestaan uit veelvuldige komponente. Weens die aard van die data, verkry vanaf
die Johannesburg Metropolitaanse Raad se twee plase (vanaf 1974 tot 1993), is slegs kalfdatum (CD),
kalf datum met 'n verswaringswaarde (CDP), kalwingsukses (CS), kalfinterval (CI), ouderdom met
eerste kalwing (AFC), langlewendheid en volhoubaarheid van die moeders om reproduktief in die
kudde tot op onderskeidelik 36, 48, 60, 72 en 84 maande te bly, bestudeer.
Kategoriese kenmerke is deur middel van 'n GFCAT stel programme, wat op 'n vadermodel gepas is,
geanaliseer. Oorerflikhede vir en die produkmoment korrelasies tussen die voorspelde teelwaardes vir
CS, langlewendheid en volhoubaarheid op onderskeidelik 36, 48, 60, 72 en 84 maande, is bereken.
Die oorerflikhede vir bogenoemde kenmerke was onderskeidelik 0.03, 0.08, 0.06, 0.10, 0.06, 0.03 en
0.11. Die korrelasie tussen die voorspelde teelwaardes vir die verskillende volhoubaarheidskenmerke
was laag. Die hoogste korrelasie, n1. 0.22, is tussen 36 en 84 maande verkry. Die oorerflikhede en
korrelasies tussen die kenmerke blyk van so 'n lae omvang te wees dat direkte seleksie vir die
kenmerke slegs tot 'n beperkte genetiese verbetering sal lei en dui daarop dat die vader slegs 'n
beperkte invloed op CS, volhoubaarheid en die langlewendheid van sy dogters het. Vir die analise van die lineere kenmerke (CI, CD, CDP en AFC), is 'n REML-prosedure gebruik wat
op 'n multikenmerk dieremodel gepas is (deur die gebruik van die REML VCE 4.2.5 pakket van
Groeneveld, 1998). Oorerflikhede vir en genetiese korrelasies tussen CI, CD, CDP en AFC is bereken
as kenmerke van die moeder. In hierdie studie is die beraamde oorerflikhede vir CI, CD, CDP en
AFC as onderskeidelik 0.01, 0.04, 0.06 en 0.40 bepaal, met herhaalbaarhede van onderskeidelik 0.07,
0.l2 en 0.13 vir CI, CD en CDP. Genetiese korrelasies tussen die kenmerke het van laag tot matig
gevarieer, behalwe vir die hoe korrelasies tussen CD en CDP (0.98), CI en CD (0.75) en CI en CDP
(0.79). Die oorerflikhede en herhaalbaarhede vir en genetiese korrelasie tussen CI en CDP verkry in
hierdie studie, veronderstel dat CD en CDP in wese dieselfde kenmerk is en dat seleksie vir CDP in
plaas van CD geen addisionele voordele inhou nie. Weens die addisionele voordele wat CD inhou, bo
die van CI, en die feit dat CD 'n minder sydige bepaling van die vroulike reproduksiekompleks is,
blyk CD van genetiese waarde te wees en moet dit as 'n moontlike seleksie kriterium, om genetiese
verbetering in 'n vleisbeeskudde te verseker, oorweeg word.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/52604 |
| Date | 03 1900 |
| Creators | Van der Westhuizen, Robert Rolfe |
| Contributors | Schoeman, S. J., Van Wyk, J. B., Stellenbosch University. Faculty of AgriSciences. Dept. of Animal Science . |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | viii, 49 p. : ill. |
| Rights | Stellenbosch University |
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