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Summary The aim of this study was to determine the egg production potentials of four different indigenous chicken breeds in South Africa: Potchefstroom Koekoek, Venda, Ovambo and Naked Neck. The White Leghorn breed was used as the control. The egg production potentials were evaluated over two consecutive production cycles of 52 weeks (used as replicates). Data were collected at the experimental farm of the Agriculture Research Council at Irene. Treatment means were separated using Fisher’s protected t-test least significant difference at the 5 percent level of significance and the percentage mortality rate by means of a row by column chi-square test. No significant differences were observed between breeds on the mean age to the production of the first egg. The White Leghorn was superior ( p ≤ 0.05) to all four of the indigenous breeds for the mean number of eggs and percentage hen-housed egg production produced per production cycle. The Potchefstroom Koekoek was also superior ( p ≤ 0.05) to the other three indigenous breeds for these parameters. There was no difference between the Ovambo and Naked Neck breeds. The percentage mortality rate for the White Leghorn (39.5 percent) was significantly ( p ≤ 0.05) different from that of the Venda, Ovambo and Potchefstroom Koekoek (22.2 percent). No differences were observed among the Potchefstroom Koekoek, Venda, Ovambo and Naked Neck (32.3 percent) or between the White Leghorn and Naked Neck with regard to the mean percentage mortality.

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No / Contrary to some popular thinking, fish do not produce a lot of eggs because so many are eaten by predators. Rather, the rate of predation on fish eggs is high because they produce such a lot of eggs. Many fish produce thousands of minute eggs, each with an infinitesimally small chance of survival because this reproductive strategy in these species results in the highest number surviving to adulthood.

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In this thesis I examine the reproductive strategies of the bed bug Cimex lectularius, a traumatically inseminating insect. In Chapter 21 examine the mating behaviour of C. lectularius, including the mating rates of males and females. Remating rates were very high, with females mating with 5 different males during a single reproductive bout. Males copulated for longer with virgin females than non-virgins. Sperm competition was predicted to be an important determinant of male reproductive success, because the ejaculates of an average of 5 males will be concurrent in the female's reproductive tract during a reproductive bout. In Chapter 3 the different gamete allocation strategies used by males were examined. Males allocated more sperm to virgin females than to non-virgins. Sperm migration and storage by females was examined in order to provide a basis from which mechanisms of sperm competition could be predicted. In Chapter 4 the patterns of sperm precedence were examined and a hypothetical mechanism of sperm competition was tested experimentally. Sperm precedence appears to favour the last male to mate due to a positional effect in the spermalege of the last ejaculate inseminated. In Chapter 5 the effect of high mating rates on females was assessed experimentally. Females mating at a high rate were found to die earlier than females mating at an artificially low rate. There was no difference in the rate of egg production of females between these two groups, so females mating at a low rate had a higher lifetime reproductive success. Appendix I investigates the potential benefits females may gain from polyandry. Both direct benefits of mating and a suite of possible fitness traits were assessed. However, no detectable differences in number or quality of offspring were uncovered. Chapter 6 reviews the evidence for a conflict of interest between the sexes over the remating rate and the possible causes of this conflict.

Native fowl populations in South Africa were characterized genetically and phenotypically. Four South African native populations, two dual-purpose breeds, and two populations from Mozambique and Botswana were included for genetic analysis. For phenotypic characterization, two commercial lines were also included as a benchmark. Twenty-three micro satellite markers were selected and tested to obtain genetic data for estimation of genetic variability and distance. Growth (weight gain) and egg production were included for phenotypic characterization. A relatively high (53% ¬64%) genetic variation was found among the populations, which suggests conservation as a genetic resource for future use. The lowest genetic variation (53%) was found for the Koekoek and Australorp populations, which are the two populations that were subjected to formal selection, while the highest variation was observed in the Naked Neck population (64%). The New Hampshire has often been included in upgrading programs and this is evident from the close relationship with both the Lebowa- Venda and Naked Neck fowls. Phenotypic trials indicated significant differences among the populations included for growth, carcass and egg production traits. The Koekoek and New Hampshire populations had the best performance for egg production and growth (weight gain) in the study. Genetic and phenotypic differences indicate that the populations can be distinguished as different breeds or groups of fowl. The results of this study may contribute to selection for improved performance for household food production, as well as conservation of the populations as a genetic resource. / Thesis (PhD)--University of Pretoria, 2001. / Animal and Wildlife Sciences / unrestricted

Mycoplasma gallisepticum (MG) is a major and economically significant pathogen of avian species. Different strains of MG have been used as vaccines in multiple-age commercial layer farms in an effort to protect the birds against more virulent field strains. The lower level of protection afforded by the low virulent MG strain vaccines provides an opportunity to the use of an overlay (revaccination) with an F-strain M. gallisepticum (FMG) later in their production cycles. In the present study, three trials were conducted to investigate the effects of prelay vaccinations of ts-11 strain MG, MG-Bacterin, or their combination, in conjunction with a FMG overlay after peak production in commercial layers. The following treatments were utilized at 10 wk of age (woa): 1) Control (no vaccinations); 2) ts-11 MG vaccine; 3) MG-Bacterin vaccine; and 4) ts-11 MG and MG-Bacterin combination. At 45 woa, all the birds in trial 1 and half of the birds in each treatment group in trials 2 and 3 were overlaid with an FMG vaccine. Various parameters including performance, internal egg and eggshell quality, blood, and visceral characteristics of the birds were evaluated. In this study, the ts-11 MG vaccination at 10 woa was shown to increase shell weight and the yolk lipid content of the eggs laid by the birds without affecting their performance. On the other hand, a prelay vaccination with MG-Bacterin did not prevent a drop in egg production in response to an overlay with FMG at 45 woa. A decrease in proportional infundibulum length in the control birds and MG-Bacterin vaccinated birds after being overlaid with FMG might be the underlying factor responsible for the observed decrease in egg production. Nevertheless, the prelay use of MG-Bacterin together with ts-11 MG didn’t appear to provide any additional benefit over the ts-11 MG vaccine alone on any of the parameters investigated. In conclusion, these results establish the potentially effective prelay use of the ts-11 MG vaccine in combination with an FMG overlay for the provision of continual protection against field strain MG infections, without eliciting any subsequent suppressive effects on the performance of commercial layers.