The genetic basis of gestation length in Bonsmara cattle
| dc.contributor.advisor | Neser, F. W. C. | |
| dc.contributor.advisor | Van der Westhuizen, J. | |
| dc.contributor.advisor | Theron, H. E. | |
| dc.contributor.author | Van Graan, Arno C. | |
| dc.date.accessioned | 2017-05-08T06:35:04Z | |
| dc.date.available | 2017-05-08T06:35:04Z | |
| dc.date.issued | 2002-11 | |
| dc.description.abstract | English: The purpose of this study was to investigate the genetic and phenotypic parameters for gestation length and birth weight in Bonsmara cattle in South Africa. The genetic and phenotypic parameters were determined when the traits were firstly treated as traits of the calf and secondly as traits of the dam. A total of 26962 gestation length and birth weight records were used for this investigation. The data was collected from 1989 to 2000. The phenotypic correlation between gestation length and birth weight was moderate and positive (0.22). The sources of non - genetic variation for gestation length and birth weight were sex, herd x year x season (HYS) and age of dam (linear and quadratic). When the traits were treated as traits of the calf all the sources of non-genetic variance were highly significant (P<0.001). Age of dam quadratic was not significant for birth weight when the trait was treated as a trait of the dam. The traits were analysed through univariate and bivariate analyses. Five basic models were used for the univariate analysis. The five models took the direct genetic, maternal genetic, and/or permanent maternal environmental genetic effects into account. The appropriate random effects were also included in, or excluded from the models. The model that fitted the data best was then used for a bivariate analysis. The direct heritability through the bivariate analysis was 0.38 for gestation length and 0.23 for birth weight. Maternal heritability was lower, 0.09 for gestation length and 0.11 for birth weight. The direct genetic correlation (0.40) and the maternal genetic correlation (0.57) between gestation length and birth weight were positive. In the above results the traits were treated as traits of the calf. The direct heritabilities for gestation length and birth weight, when the traits were treated as traits of the dam, were 0.15 and 0.16 respectively through bivariate analysis. The maternal heritabilities for gestation length and birth weight were very low to negligible (0.02 and 0.003). The direct genetic correlation (0.41) between gestation length and birth weight was positive, but the maternal genetic correlation (-0.83) was negative. Estimated breeding values (EBVs) for gestation length and birth weight were calculated for each animal in the data. The genetic trends for gestation length and birth weight were also determined. The trend for gestation length showed that there was a correlated response for shorter gestation length through the possible direct selection for lower birth weight. The trend for birth weight showed that there was selection for lower birth weight. | en_ZA |
| dc.description.abstract | Afrikaans: Die doel van die studie was om die genetiese en fenotipiese parameters van dragtigheidslengte en geboortegewig in Bonsmara beeste te ondersoek. Eerstens is die genetiese en fenotipiese parameters bereken wanneer die eienskappe as 'n meting van die kalf hanteer is. Tweedens is die eienskappe as 'n meting van die moeder hanteer. 'n Totaal van 26962 dragtigheidslengte en geboortegewig rekords is vir die ontledings gebruik. Die data het oor die tydperk 1989 tot 2000 gestrek. Die fenotipiese korrelasie was positief (0.22). Die bronne van nie-genetiese variasie was geslag, kudde x jaar x seisoen (HYS) en ouderdom van moeder (Iineêr en kwadraties). AI die bronne van nie-genetiese variasie het 'n betekenisvolle (p<0.001) invloed op die berekeninge gehad. Bogenoemde het gegeld ten opsigte van die hantering van die eienskappe as 'n meting van die kalf. Waar die eienskappe as 'n meting van die moeder hanteer is, was die effek van ouderdom van moeder (kwadraties) vir geboortegewig nie betekenisvol (P<0.001) nie. Die eienskappe is ontleed deur enkelkenmerk- en multikenmerk ontledings. Vyf basiese modelle is gebruik vir die enkelkenmerk ontleding. Hierdie modelle het die direk genetiese, maternaal genetiese en permanente maternale omgewing genetiese effekte in berekening gebring. Die toevallige effekte is ook in- of uitgesluit in die ontledings. Die model wat die data die beste verklaar het is gebruik vir die multikenmerk ontleding. Die direkte oorerflikheid is 0.38 vir dragtigheidslengte en 0.23 vir geboortegewig. Maternale oorerflikhede was laer, 0.09 vir dragtigheidslengte en 0.11 vir geboortegewig. Bogenoemde resultate is verkry toe die eienskappe hanteer is as 'n meting van die kalf. Die genetiese korrelasies (direk en maternaal) tussen dragtigheidslengte en geboortegewig was positief (0.40 en 0.57). In die geval waar die eienskappe as 'n meting van die moeder hanteer is, is heelwat laer oorerflikhede verkry. Die direkte oorerflikheid vir dragtigheidslengte en geboortegewig was 0.15 en 0.16. Maternale oorerflikhede vir dragtigheidslengte en geboortegewig in die geval was 0.02 en 0.003. Die direkte genetiese korrelasie tussen dragtigheidslengte en geboortegewig is in die geval positief (0.41) maar die maternale genetiese korrelasie is negatief (-0.83). Teelwaardes vir dragtigheidslengte en geboortegewig is bereken vir al die individuele diere in die data. Die genetiese tendense is ook bereken vir dragtigheidslengte en geboortegewig. Die genetiese tendens vir dragtigheidslengte toon aan dat dit korter geword het oor die jare as gevolg van die gekorreleerde respons op seleksie vir laer geboortegewigte. Die genetiese tendens van geboortegewig toon aan dat daar geselekteer is vir laer geboortegewigte. | af |
| dc.identifier.uri | http://hdl.handle.net/11660/6179 | |
| dc.language.iso | en | en_ZA |
| dc.publisher | University of the Free State | en_ZA |
| dc.rights.holder | University of the Free State | en_ZA |
| dc.subject | Bonsmara cattle -- Pregnancy | en_ZA |
| dc.subject | Beef cattle -- Breeding | en_ZA |
| dc.subject | Dissertation (M.Sc.Agric. (Animal, Wildlife and Grassland Sciences))--University of the Free State, 2002 | en_ZA |
| dc.title | The genetic basis of gestation length in Bonsmara cattle | en_ZA |
| dc.type | Dissertation | en_ZA |