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A total of 7,472 progeny from 4 lines of chickens, a Black Australorp, a New Hampshire and 2 Leghorn lines, their crosses and reciprocal crosses were assessed for their pre- and post-hatching body weights, pre- and post-hatching growth rates and their associated egg weights. The interrelationships of these traits as they influenced growth and 7-week body weight were evaluated. The effects of these relationships were jointly considered as they influenced the genetic variation and subsequent estimates of the heritability (h²) of these traits. The results of the investigation showed that an adverse environmental effect due to hatching was definitely established. It took 2 weeks of growth after hatching for the chicken body weights to attain the same level of association with 7-week body weight that was previously shown in the body weights of 18-day old embryos. Multiple regression analyses showed that 1-week body weight and any subsequent growth periods successfully accounted for variation in 7-week body weight. The h² estimates obtained for all weekly growth rates as well as the 1-3, 3-7, and 1-7 week growth rates strongly indicated a major source of additive genetic variance was available in poultry populations that heretofore has not been directly utilized in body weight selection programs. / Land and Food Systems, Faculty of / Graduate

A study was conducted to make a genetic evaluation of egg mass (weight of the total eggs laid in a given period) in order to determine its genetic potential as a new criterion for selection as compared to the conventional selection program based on egg number (early and full production records). In addition, biometrical evaluations of some egg component traits: yolk weight, albumen weight, shell weight, percent yolk, percent albumen, percent shell, albumen percent solid, yolk percent solid, yolk percent protein, albumen percent protein, yolk solid and albumen solid were made. The aforementioned traits were measured on 3 random bred lines of chickens in quarterly periods through the laying year. Within each line, the heritability estimates of egg number and egg mass for any given period (275, 325, 450 and 540 days of age) were found to be in close agreement. In general, for egg number and egg mass, selection from early production records showed higher gains per unit of time than full year production records, A negative genetic correlation between egg number traits and egg weight traits and a positive genetic correlation between egg mass and egg weight traits was found, therefore, selection for egg mass was recommended. Relative merit of early and full year egg records as selection criterion was discussed in the light of the results obtained for the three lines. It was concluded that the decision as to which criterion should be used would have to depend upon the genetic properties of the population in question. Line effects were found to be significant for all the egg component traits studied, except percent shell, A season-age effect was also found to be significant in all the traits studied. Season-age by sire interactions were found to be non-significant for all the traits in all the three lines. The importance of yolk size from a human nutrition standpoint was discussed. A selection program based on total yolk weight produced by a hen in a given period (yolk mass) was suggested. Because of the water in the egg being an essential nutrient for the developing chick embryo, it was suggested that selection be made on the egg solid or egg solid mass (total amount of solid laid by a hen in a given period). The heritability estimates of albumen percent solid and albumen percent protein were high and of the same magnitude. It was, therefore, suggested that an increase in percent protein in albumen should be achieved by selection of albumen percent solid. / Land and Food Systems, Faculty of / Graduate

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Call number: LD2668 .T4 1953 S6 / Master of Science

Certain types of infertility found in various animal populations may be due to genetic causes. This type of lowered reproduction becomes increasingly important in the male as the use of artificial insemination extends to more species. The extensive use of affected males tends to increase the frequency of these deleterious alleles in a population and thus lower the rate of reproduction of the species. [...]

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Introduction : Family Poultry (FP) are birds of indigenous breeds living in almost symbiotic relationship with human communities. The chickens are usually free ranging, or have very limited restrains on their access to the village environment. African livestock population statistics for 1995 indicates poultry to be the most numerous species of farm animal (Anonymous, 1996a). More than 80% of poultry are kept in rural areas and contribute substantially to annual egg and meat production (Sonaiya, 1997). Throughout Africa poultry production stems from ancient traditional practices. FP is the most important type of poultry kept on the continent. In general, village producers keep small flocks of between 5 and 20 birds per household (Gueye, 1997a). Women and children play a key role in their management (Kitalyi, 1996). Because of its productivity, FP production has been neglected and is frequently considered by farmers as an insignificant occupation compared with other agricultural activities. Nevertheless, outside urban centers and especially in non-coastal areas, FP provides the population with a vital source of protein and income. In addition, they play an important role within the context of many social and/ or religious ceremonies. Although this type of poultry constitutes an important part of food security for rural households in South Africa, scientists have not explored this area of research for improving or recording this production system. Yet, FP survived for decades without being wiped out, in the interim, their keepers have gathered and stored a wealth of knowledge and experience, ensuring the survival of this genetic resource. The objective of this study was to collect the baseline data on FP production systems, determine their production constraints and achieve data for future use in the intervention strategies.

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