Doctoral Degrees (Animal Sciences)

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Browsing Doctoral Degrees (Animal Sciences) by Author "Cloete, Jasper Johannes Erasmus"

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    Evaluation of the South African small stock genetic resources for production and meat quality traits
    (Stellenbosch : Stellenbosch University, 2007-03) Cloete, Jasper Johannes Erasmus; Hoffman, Louwrens C.; Cloete, Schalk W. P.; Stellenbosch University. Faculty of AgriSciences. Dept. of Animal Sciences.
    ENGLISH ABSTRACT: The study includes separate papers, which are all linked by their emphasis on the evaluation of South African small stock genetic resources for production and meat quality. This abstract is intended to provide readers with a broad overview of the outcomes of the study. Part 1: Comparison of breeds Chapter 2 dealt with the slaughter and meat quality traits of wool (Merino), dual-purpose (Dohne Merino and South African Mutton Merino (SAMM)) and meat type (Dormer) sheep. The more expensive retail cut weights were higher in the meat type sheep but the latter breeds also had a thicker fat cover. Dormer and SAMM sheep had heavier but fatter carcasses than Merinos and Dohne Merinos, with no marked differences in meat quality among breeds. Chapter 3 provides production parameters obtained from Merino, Dohne Merino and SAMM stud flocks. An economic simulation indicated differences in gross income per small stock unit between the breeds. Merinos generally outperformed the other two breeds in terms of income per small stock unit. In Chapter 4, Dorper, Merino and Boer Goat breeds were compared on reproduction potential. Reproduction and growth of the three breeds were comparable with figures found in the literature. An economical analysis indicates that Merino ewes outperformed the other two breeds in terms of income per small stock unit. Part 2: Assessment of Merino and Merino type ewe breeds as terminal dam lines Chapter 5 details the production performance of ewes that originated from a terminal crossbreeding experiment that involved five Merino type dam lines and two terminal crossbreeding sire lines (Dormer and Suffolk). In Chapter 6 slaughter data and meat quality of the crossbred progeny were compared and discussed. Differences between progeny in slaughter age, marketing weight, dressing percentage and carcass weight could largely be attributed to the comparison of purebred Merino lines with dual-purpose lines. In Chapter 7 an economic simulation indicated large differences in gross income per small stock unit between ewe lines. Chapter 8 provides details of slaughter traits of lambs born from a terminal crossbreeding experiment that involved Merino ewes crossed with Dormer, Ile de France, Merino Landsheep, Suffolk and Dorper rams, purebred Merinos were used as control. No conclusive advantages in favour of any of the terminal sire breeds were obtained. Part 3: Importance of carcass quality using leaner sire breeds on early maturing Dorpers In Chapter 9 Dorper ewes were crossed with Ile de France, Merino Landsheep and SAMM rams to produce lean carcasses without sacrificing growth performance. Terminal crossbred lambs were equal to or superior to purebred Dorpers with regard to quantitative and qualitative carcass parameters evaluated (Chapter 10). SM2000 economic simulation model was used to assess the economic output of the respective breed combinations and discussed in Chapter 11. No real differences were found for income per small stock unit between the different crossbred combinations and purebred Dorper lambs. Terminal crossbreeding could thus be implemented in commercial Dorper flocks, without compromising productivity and/or product quality. Implications The study revealed marked differences in the performance of the breeds contributing to the South African small stock genetic resource. As with other experiments with finite monetary and animal resources, animal numbers (and especially those of sires sampled to represent a breed) were relatively low. Further studies on the evaluation of the South African small stock genetic resource is indicated. Studies on the integration of sheep breeds in structured crossbreeding systems should have a high priority, since it appears to be a sustainable way to ensure economic viability of commercial small stock production.