Thesis (M.Sc.) (Agriculture) --University of Limpopo, 2007 / The objectives of this study were to evaluate the effect of pre-weaning selection on estimates of genetic parameters for post-weaning average daily gain in Phases C (ADG-C) and D (ADG-D) and to estimate genetic relationships between average daily gain in the two phases. Performance records of the South African Angus cattle breed was used in the analysis. (Co)variance components and genetic parameters for weaning (WWT), AGD-C and ADG-D were estimated by REML procedures fitting three different models (Models 1, 2 and 3) that differed in how they integrated sequential selection in the analysis of post-weaning traits. Model 1 was a univariate model of WWT, ADG-C and ADG-D. Model 2 was a two trait model of WWT and either ADG-C or ADG-D. Model 3 was a three trait model of WWT, ADG-C and ADG-D. Estimates of heritability for ADG-C were 0.39±0.08, 0.42±0.06 and 0.44±0.01 from Model 1, 2 and 3 respectively. Corresponding estimates of heritability for ADG-D were 0.18±0.021, 0.19±0.021 and 0.21±0.02 respectively. An estimate of genetic correlation between ADG-C and ADG-D was 0.58± and it suggested that the two traits may not necessarily be under the same genetic control. Rank correlations for all bulls based on ADG-C estimated breeding values (EBV’s) were 0.92, 0.83 and 0.94 for Model 1 vs. Model 2, Model 1 vs. Model 3 and Model 2 vs. Model 3 respectively. Corresponding ADG-D EBV’s rank correlations were 0.88, 0.84 and 0.93. Rank correlations for top and bottom 1%, 5% and 10% were lower than those for all bulls in both ADG-C and ADG-D. Low rank correlations showed that the difference in magnitude of genetic parameters from different models was enough to alter bull rankings based on EBV’s of ADG-C and ADG-D. Hence it was concluded that inclusion of pre-weaning information in genetic analysis for post-weaning average daily gain is necessary to account for selection at weaning. / the THRIP (Technology and Human Resource for Industry Project) and NRF (National Research Foundation).

Explanatory feeder cattle basis models were developed for 16 different Virginia markets by season, futures contract month, weight, lot size, sex, breed and USDA grade differentials. The models are more disaggregated and explain up to 80 percent more of feeder cattle basis variation than any previous research. Since the variables in these explanatory models are all known in advance, these basis models are also predictive. Basis estimates from these models make it possible for a Virginia feeder cattle forward pricing agency to offer forward price and minimum price contracts to small size operators. / Master of Science

Die Milchgarantiemengenregelung der EU hat nur noch eine vorgesehene Laufzeit bis 2008, welche Regelungen danach gelten werden, ist noch unklar. Um für die Zuchtplanung bei Milchrindern die ökonomisch-genetische Gewichtung der Milchleistungsmerkmale bei zukünftigen wirtschaftlichen Rahmenbedingungen zu erhalten, wurde ein Selektionsindexes erstellt. Als Datenmaterial dienten die Ergebnisse der Milchleistungsprüfungen der Kühe des Rinderzuchtverbandes Mecklenburg-Vorpommern. Hieraus wurden die genetischen Parameter für die Milchleistungsmerkmale Fettmenge, Eiweißmenge, Fettgehalt und Eiweißgehalt sowie für die Verzögerungszeit mit den Computerprogrammen SAS, PEST und VCE4 geschätzt. Diese Merkmale wurden dann in Selektionsindices aufgenommen, welche die derzeitige genetische Struktur der Rinderpopulation in Mecklenburg-Vorpommern und die zukünftig zu erwartenden politischen Rahmenbedingungen berücksichtigen. Zur Aufstellung der Selektionsindices wurden mehrere Varianten einer Liberalisierung des EU-Milchmarktes mit Hilfe des SWOPSIM-Marktmodels simuliert und für die Milchinhaltsstoffe Milchfett und Milcheiweiß die Marktpreise geschätzt. Das Preisniveau wird nach diesen Schätzungen nach einer Marktliberalisierung für Rohmilch bei ca. 0,22-0,25 €/kg liegen, für Milchfett bei ca. 2,05-2,25 €/kg und für Milcheiweiß bei ca.3,89-4,45 €/kg. / The Milk-Quota-System of the European Union will probably end in 2008. It is not clear which arrangement will prevail afterwards. A selection index was built to get the economic-genetic weights of different traits for the breeding-planning of dairy-cattle for future conditions. The data was taken from the milk-yield-testings of the cattle breeding organisation of Mecklenburg-Vorpommern. From these data the genetic parameters for fat yield, protein yield, fat content, protein content and the time from the first to the successfully insemination was estimated with the computer programs SAS, PEST and VCE4. With these traits a selection index was built which contains the actual genetic structure of the Mecklenburg-Vorpommern cattle population and the future economic and political conditions. To get the future economic parameters, different variants of liberalization of the European milk market had been simulated with the SWOPSIM-framework. Market prices for milk fat and milk protein have been estimated. After a liberalization in the EU the price level will be 0,22-0,25 €/kg for raw milk, 2,05-2,25 €/kg for milk fat and 3,89-4,45 €/kg for milk protein.

The theoretical part of the thesis entitled "Accuracy of loading into a hanging horizontal feed wagon" deals with the historical development of feed administration of cattle and currently used trends in feeding. The diploma part also describes the basic technology of production of bulky and fodder fodder, there is also a modern technology for their distribution, characteristics and the way of loading individual components of the ration, which also includes the evaluation of loading of individual components. The thesis also deals with the choice of mixing feed wagon. The practical part is focused on the evaluation of loading accuracy into the hanging horizontal feed wagon.

Dairy farming is one of the most important agricultural industries in South Africa, and thus improving the performance of dairy cows, with respect to economically important dairy traits, would be beneficial. Selection of dairy cows has traditionally been phenotypic, but new molecular techniques have made it possible to evaluate phenotypic dairy traits at the DNA level, providing the possibility of more accurate selection. The economically important dairy traits, milk production and reproductive performance, are quantitative traits, and are therefore controlled by many genes and the environment. A number of genes have been identified that have been shown to influence economically important dairy traits, including the lep gene. This gene encodes the hormone leptin, which has been proven to regulate feed intake, energy balance, fertility and immune function. A polymorphism has been identified in the lep gene, which may be associated with economically important dairy traits. This study on a South African Jersey herd investigated the possible association of the polymorphism, RFLP-Kpn 21, with milk production and reproductive performance. The lactation records of fifty Jersey cows that completed their first lactation between 1997 and 2004 were collected, and these cows were genotyped for the RFLP-Kpn 21 polymorphism, located at exon 2 of the lep gene. This involved the extraction of DNA from venous blood, using a salting out technique. The extracted DNA was amplified using PCR primers; the reverse primer included a purposeful mismatch. The role of the purposeful mismatch was to create a recognition site for a restriction enzyme (Kpn 21), thus allowing the alleles of the polymorphism to be identified through a restriction digestion protocol. Two alleles were identified, the C- and the Tallele. The genotype of each cow was identified using PAGE. The significance of the genotype effects on the milk production traits and the reproductive performance traits were estimated using the F-statistic provided by a GLM Univariate analysis. In conclusion, no significant effect of the RFLP-Kpn 21 polymorphism was found for milk yield, butterfat and protein percentage, ICP and SPC (p > 0.05), but a possible association with lactose percentage was suggested by the statistical analysis (p < 0.05). Further investigation of South African Jersey cows will be necessary in order for conclusive results to be obtained. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2005.

The face of animal breeding has changed significantly over the past few decades. Traditionally, the genetic improvement of both plant and animal species focussed on the selective breeding of individuals with superior phenotypes, with no precise knowledge of the genes controlling the traits under selection. Over the past few decades, however, advances in molecular genetics have led to the identification of genetic markers associated with genes controlling economically important traits, which has enabled breeders to enhance the genetic improvement of breeding stock through linkage disequilibrium marker-assisted selection. Since the integration of marker-assisted selection into breeding programmes has not been widely documented, it is important that breeders are able to evaluate the advantages and disadvantages of marker-assisted selection, in comparison to phenotypic selection, prior to the implementation of either selection strategy. Therefore, this investigation aimed to develop deterministic simulation models that could accurately demonstrate and compare the effects of phenotypic selection and marker-assisted selection, under the assumption of both additive gene action and complete dominance at the loci of interest. Six computer models were developed using Microsoft Excel, namely 'Random Mating,' 'Phenotypic Selection,' 'Marker-Assisted Selection,' 'Selection with Dominance,' 'Direct Selection' and 'Indirect selection.' The 'Random Mating' model was firstly used to determine the effects of linkage disequilibrium between two loci in a randomly mating population. The 'Phenotypic Selection' and 'Marker-Assisted Selection' models focused primarily on examining and comparing the response to these two selection strategies over five generations and their consequent effect on genetic variation in a population when the QTL of interest exhibited additive gene action. In contrast, the 'Selection with Dominance' model investigated the efficiency of phenotypic selection and marker-assisted selection under the assumption of complete dominance at the QTL under selection. Finally, the 'Direct Selection and 'Indirect Selection' models were developed in order to mimic the effects of marker assisted selection on two cattle populations utilizing both a direct and indirect marker respectively. The simulated results showed that, under the assumption of additive gene action, marker-assisted selection was more effective than phenotypic selection in increasing the population mean, when linkage disequilibrium was present between the marker locus and the QTL under selection and the QTL captured more than 80% of the trait variance. The response to both selection strategies was shown to decrease over five generations due to the decrease in genetic variation associated with selection. When the QTL under selection was assumed to display complete dominance, however, marker-assisted selection was markedly more effective than phenotypic selection, even when a minimal amount of linkage disequilibrium was present in the population and the QTL captured only 60% of the trait variance. The results obtained in this investigation were successful in simulating the theoretical expectations of markerassisted selection. The computer models developed in this investigation have potential applications in both the research and agricultural sectors. For example, the successful application of a model developed in this investigation to a practical situation that simulated markerassisted selection, was demonstrated using data from two Holstein cattle populations. Furthermore, the computer models that have been developed may be used in education for the enhancement of students understanding of abstract genetics concepts such as linkage disequilibrium and marker-assisted selection. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2006.

Leptin, a 16 (kilo Dalton) kDa hormone secreted predominantly by white adipocytes, regulates reproduction, energy intake and expenditure, and is involved in immune system function. Previous studies have identified associations between polymorphism E2FB in the leptin gene (lep) of cattle and milk quality and quantity, feed intake, and fat deposition in dairy and beef cattle though further studies have shown inconclusive results. Furthermore, indigenous South African cattle have not been involved in lep investigations or the applicability of the marker in South African beef grading systems. An investigation was conducted into the association of an SNP of a cytosine (C) to thymine (T) SNP (single nucleotide polymorphism) mutation in exon 2 of the bovine lep (leptin) gene with weight gain, body condition, carcass fat content and quality in a population of indigenous Nguni cattle (n = 70) as well as a population of exotic British Hereford cattle (n = 54). The Hereford population had higher T-allele frequencies and a lower P-value (P = 0.172) for the E2FB genotypes than the Nguni population (P = 0.958). The resulting E2FB lep genotypes CC, CT and TT did not show an association with the pre- and post-slaughter traits initial live weight (ILW), body condition score (BCS), slaughter live weight (SLW), carcass fat content (FAT), carcass conformation (CFN) or warm carcass mass (WCM) for either population though t-tests revealed an association with the CT genotype with increased ILW than TT and a significantly higher WG in the TT genotypes than the CT (P<0.05). Subsequently, differences in pre- and post-slaughter traits in both populations were largely attributable to breed differences. The Hereford population exhibited significantly higher WG, CFN, SLW, WCM and CCM (P<0.05) than the Nguni population. The Nguni displayed significantly higher ILW and BCS values when graded in terms of the commercial South African AAA feedlot system. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2010.

No description available.

No description available.

No description available.