The present study was carried out to estimate genetic, phenotypic and environmental
parameters for growth traits, genetic trends as well as the level of inbreeding in the South
African Brahman breed. The data used were obtained from the South African Brahman
Breedersâ Society and consisted of pedigree information of 181 508 animals and 221 015
performance records, ranging from birth to 18-months weight /final weight collected
between 1955 and 2002. Performance records available before editing as classified
according to age ranges were birth weight (BWT) = 67 336, weaning weight (WWT)
(80â300 days) = 62 159, yearling weight (YWT) (301-500 days) = 41 313 and final
weight (FWT) (501-900 days) = 32 602. The linear animal model used included the fixed
effects of contemporary group (herd-year-season), sex, management group, age of the
calf, age of the dam. Direct genetic, maternal genetic and permanent maternal
environmental as random effects as well as sire x herd-year-season interaction as an
additional random effect. Preliminary analyses showed that all fixed effects had a
significant (P<0.0001) effect on all traits studied.
Genetic parameters for growth traits were estimated using ASREML software by fitting
univariate and bivariate animal models. Production traits considered after editing were
BWT = 41 509, WWT = 37 705, YWT = 22 682 and FWT = 13 055 records collected
between 1985 and 2002. The reason for using the data only from 1985 is that only a small
number of records were recorded up to 1984. The direct heritability estimates of BWT,
WWT, YWT and FWT were 0.28, 0.14, 0.14 and 0.18 respectively. The corresponding
maternal heritability estimates were 0.11, 0.06, 0.05 and 0.03 respectively. The maternal permanent environmental component due to the dam contributed 3 - 7 % of the total
phenotypic variance of the traits under consideration. The corresponding contribution of
sire x herd-year-season interaction ranges from 5 - 6%. The genetic correlation between
animal effects was -0.36 for BWT, other traits studied did not show an antagonism
between animal effects. The prospects of improvements of these traits by selection seem
possible and the contributions of permanent maternal environmental effect are not
equally important as maternal effects though the effects are small.
Estimates of phenotypic correlations were low to moderate (0.22 to 0.64), whereas
genetic correlations were moderate to high (0.47 to 0.91). Genetic correlations between
BWT and WWT, YWT and FWT were 0.62, 0.47, and 0.52 respectively. The
corresponding genetic correlations between direct and maternal effects of the same trait
(ram, rma) were (-0.4204, -0.014), (-0.4241, 0.0567) and (0.05170, 0.0879) respectively.
Genetic correlations between WWT and postweaning weights were 0.88 and 0.91 for
YWT and FWT respectively. The corresponding maternal correlation was at unity.
Lastly, the genetic and maternal correlation between YWT and FWT were 0.83 and unity,
respectively.
Positive genetic trends were observed for all traits except for the maternal genetic trend
for BWT, which had a slightly negative slope. Direct genetic progress for BWT was
0.0207 kg/year (1987-2002), whereas progress for WWT was 0.1kg/year (1985-1995)
and 0.4 kg /year (1996-2001). Progression in direct genetic effect for YWT was
0.1kg/year (1985- 1995) and 0.3 kg/year (1996-2001) whereas progress for FWT was
0.13 kg/year (1985-2001). The maternal genetic trends were -0.003, 0.04, 0.008 and 0.003 kg/year for BWT, WWT, YWT and FWT, respectively. Genetic progress was in
general low over the years for all traits. Therefore, estimation based on BLUP of breeding
values may be more important in the future and should be considered to maximise
opportunities for genetic change.
Inbreeding level and its possible influence on growth traits of the South African Brahman
cattle were investigated. Inbreeding coefficients were calculated by inverting the diagonal
of the inverse relationship matrix using the MTDFNRM program of the MTDFREML
package. Inbreeding depression was estimated as the regression of performance on
individual and dam inbreeding coefficients using an animal model. The mean inbreeding
of the population was very low (0.01) with an average of (0.03) for inbred animals.
Although regression coefficients of BWT, WWT, YWT and FWT on inbreeding of
animal and dam were significant for all traits, the results showed that inbreeding at
present is not a serious problem in the South African Brahman breed.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ufs/oai:etd.uovs.ac.za:etd-09292005-160524 |
| Date | 29 September 2005 |
| Creators | Pico, Boipuso Alpheus |
| Contributors | Prof FWC Neser, 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-09292005-160524/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. |
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