1. The purpose of the first chapter was to give a short introduction to the study. Although there were
exponential increases in knowledge, there are still fields of study where there is little understanding
and enormous gaps relating to information. A short history of the development of cattle was presented,
with special reference to the Simmentaler breed. The objectives of this study were then stated. These
objectives were: the definition of breeding objectives, derivation of economic values and development
of economic selection indices for the Simmentaler breed in South Africa.
2. In Chapter 2 the development of breeding objectives and the derivation of economic values were
reviewed. There seems to be general consensus that definition of breeding objectives should be the
primary step in the design of structured breeding programs. Development of the breeding objective
can be described in terms of the following phases: specific ation of the breeding, production and
marketing system, identification of sources of income and expense in commercial herds, determination
of biological traits that influence income and expense, derivation of economic values, choice of
selection criteria, and estimation of phenotypic and genetic parameters. The modeling methods to
derive economic values can be divided into simulation, dynamic programming and profit functions.
3. In Chapter 3 the important traits, which should be considered for the development of breeding
objectives, as well as the criteria to be included in the selection index were reviewed. Traits were
classified as fitness-, production-, product-, input-, type- and behavioural traits. The decision whether
or not to include a trait in the breeding objective depends on the relative economic value of the trait,
the potential for genetic improvement and the possibility of accurate and cheap measurement. Several
traits determine economic efficiency, and the required balance of these traits is likely to differ between
different production systems.
4. The purpose of Chapter 4 was the development of a general breeding objective for the Simmentaler
breed in Southern Africa as well as the derivation of economic values for beef production traits.
Income was partitioned between weaners (steers), surplus heifers and cull cows. Expenses were
calculated for all classes and included feed cost, husbandry cost and marketing cost. Economic values
for weaning weight (direct), weaning weight (maternal), yearling weight (400 days), final weight (600
days) and mature cow weight were derived as partial derivatives of the profit equation. These values,
expressed per genetic standard deviation, in South African Rand per cow, corrected with the
discounted gene flow and diffusion coefficient methods (in brackets) are, 25.57 (75.01), 15.21 (47.97),
28.49(83.63), -13.95 (-40.79) and -69.29 (-63.39) respectively.
5. The objectives of Chapter 5 were to expand the Simmentaler breeding objective by inclusion of
functional traits and to derive economic values for the functional traits calving rate, days -to-calving,
calving-ease (direct) and calving-ease (maternal). It was assumed, for these categorical traits, that
there is an unobserved underlying normal distribution of the sum of genetic and environmental values,
and that the phenotypic category is defined by threshold values on this distribution. The consequences
of a change in fitness included changes in costs, changes in culling rate, number of barren cows and
the number of surplus offspring available for sale. Results emphasised the relative importance of
fertility. Economic values, expressed per genetic standard deviation in South African Rand per cow,
corrected with the discounted gene flow and diffusion coeffic ient methods (in brackets) are, 18.98
(15.27), - 93.82 (- 75.51), 1.08 (1.31) and 1.15 (1.08) for calving rate, days-to-calving, calving-ease
(direct) and calving-ease (maternal), respectively.
6. The objectives of Chapter 6 were to expand the Simmentaler breeding objective by the inclusion of
product quality traits and to derive economic values for dressing percentage, backfat thickness,
tenderness and marbling. A method to derive economic values for these optimum traits was described.
It was as sumed, for the categorical traits, that there is an unobserved underlying normal distribution of
the sum of genetic and environmental values, and that the phenotypic category is defined by threshold values on this distribution. The consequences of a change in the mean performance of a trait include
changes in the number of animals in different quality classes and as a result thereof, changes in the
expected value of a carcass. Economic values, expressed per genetic standard deviation in South
African Rand per cow, corrected with the discounted gene flow and diffusion coefficient methods (in
brackets) are, 20.96 (61.50), 0.39 (1.14), -3.52 (-10.33) and 0.18 ( 0.52) for dressing percentage,
backfat thickness, tenderness and marbling respectively.
7. The development of economic selection indices for an integrated Simmentaler production system was
described in Chapter 7. The breeding objective was defined in terms of production-, functional- and
product quality traits. Criteria included in the total index are birth- and weaning weight (direct and
maternal), yearling weight, final weight, mature cow weight, days -to-calving, backfat thickness,
tenderness and marbling. The total merit index (IT) for an integrated Simmentaler production system is
IT = â 1.65 BWD â 1.99 BWM + 2.28 WWD + 1.76 WWM + 1.48YW â 0.50 FW â 2.02 MCW â 13.21
CD + 4.92 BF â 2.34 T + 12.77 M. The correlation between this index and the breeding objective is
0.987. The economic superiority, over the average progeny, of the progeny from the top 40% of
animals selected on their ranking in the total index, is expected to be R116.49.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ufs/oai:etd.uovs.ac.za:etd-09292005-155554 |
| Date | 29 September 2005 |
| Creators | Kluyts, Johan Francois |
| Contributors | Prof FWC Neser, Dr MJ Bradfield |
| 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-09292005-155554/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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