Genetic (co)variances for yearling body weight (BW), clean fleece weight (CFW)
and mean fibre diameter (MFD) in the SA Dohne Merino population were estimated
using records of 107 389 animals recorded between 1992 and 2004. The data
include records of 1 530 sires and 45 178 dams. An animal model with direct and
maternal additive, maternal permanent and temporary environmental effects was
fitted for all traits. Sire-flock (SF) and sire-flock-year-season (SFYS) was included
as additional random effects. Fixed effects were (FYSSM) (1594 classes), type of
birth (singles, multiples), age of dam (2 to 7+ years) and average age (± SD) at
measurement fitted as a linear covariate (385 ± 12 days). Estimates obtained by
single -trait analyses were used as starting values in three-trait analyses.
The direct genetic heritability estimates for FD, CFW and BW obtained from the
three-trait analysis were 0.447 (0.009), 0.216 (0.008) and 0.277 (0.008) respectively.
The genetic correlations were 0.050 between BW and CFW, 0.100 between BW and
FD and 0.139 between FD and CFW. The phenotypic correlations were 0.318
between BW and CFW, 0.129 between BW and FD and 0.180 between FD and
CFW. Direct genetic correlations of BW, CFW and MFD were positive, which
suggest that selection for bigger and heavier sheep would generally lead to a
stronger MFD and higher CFW. Because these values are very low the subsequent
effect of this phenomenon would be that the effect of selection for body traits on
fleece traits would be very small and vice versa.
Genetic trends were calculated using the annual average breeding value estimates
(EBV) for each trait. According to the genetic trends derived, the selection policy
followed did cause genetic change in the traits studied, even though it was slow.
The level of inbreeding (F) in the South African Dohne Merino sheep population is
very low. The proportion of animals that was inbred to some extent increased from
0% (average F=0) in 1980 to 38% in 2003 (average F=1.22%). No significant
inbreeding depression on BW, CFW and MFD could be found. In general the results suggest that inbreeding at present is not a serious problem in the South African Dohne Merino breed.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ufs/oai:etd.uovs.ac.za:etd-02282007-090448 |
| Date | 28 February 2007 |
| Creators | Swanepoel, Jan Willem |
| Contributors | Dr GJ Delport, Prof SWP Cloete, Prof JB van Wyk |
| Publisher | University of the Free State |
| Source Sets | South African National ETD Portal |
| Language | en-uk |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.uovs.ac.za//theses/available/etd-02282007-090448/restricted/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University Free State or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
Page generated in 0.002 seconds