Chicken meat is an important source of high quality protein in the diet of most people in the world. Consequently, the increasing demand for this meat has made chicken meat production the most important growth sector among other meat species. This has been achieved by a half century of intensive genetic selection for growth traits; however, this was coupled with poor reproductive performance of broiler breeders. Ross 708 represents a broiler breeder strain that has been developed for breast-meat yield, and has been reported to exhibit poor reproductive performance in comparison to Ross 308, a typical broiler breeder strain. Accordingly, the current study investigated key points involved in the reproductive process that might influence variation in reproductive performance. Ovarian follicles number was the first point to investigate, as they are the main material of the egg. Liver fatty acid profiles were also investigated in order to identify lipid metabolism and the efficiency of dietary fat utilisation, as the liver is the main site that supplies different body tissues with fatty acids. Carcass fat content was also examined as its negative relationship with reproduction is well documented. Finally, the content of calcium in the tibia bone was examined to identify whether variation in egg production was associated with differences in the metabolism of this element. Accordingly, broiler breeder females from Ross 308 and 708 strains, reared under the standard production system on two different commercial farms of PD Hook, were collected throughout the reproductive cycle; starting at 25-week-old and in five weeks interval until 55-weeks of age. Findings showed no difference in the number of both the large yellow follicles (P=0.332), and the small yellow follicles (P=0.134); whereas the number of large white follicles was higher in the 708 ovaries (P=0.005). Differences in lipid metabolism were identified with a strong tendency for the 708s towards having lower content of linoleic acid (P=0.056) in addition to significantly lower a-linolenic acid (P=0.005). Of particular importance is the latter fatty acid as it is the precursor to (n-3) fatty acids, some of which were found to be less (P<0.001) in the 708s including docosapentaenoic (DPA) and docosahexaenoic (DHA). The importance of these fatty acids in follicular maturation is well documented in addition to the importance of the linoleic acid; these findings indicate that the 708s were not receiving adequate levels of the essential fatty acids which might have contributed to their poor reproductive performance. The 708s also laid down significantly more fat (P<0.001) in comparison to the 308s which could be another factor that has impaired their reproduction performance. This could indicate different levels of metabolic hormones which, in turn, have been found to act in concert with the reproductive hormones. 708s also exhibited a trend towards lower content of calcium in their tibiae, with an age by strain interaction and thus suggesting a difference in the metabolism of this element at some ages. The current study has addressed changes of the investigated parameters with age, but the effect of genetic selection on reproductive performance was difficult to address. Rather, some physiological differences have been identified; 708s were found to be receiving inadequate amounts of essential fatty acids, calcium content was found to be less at some ages and they exhibited a higher content of carcass fat. All these factors have the potential to contribute to poor reproductive performance, and once they are taken into consideration better assessment for the effect of the continued genetic selection for more growth traits can investigated.

Thesis (M.Sc. Agric.(Animal Science)) --University of Limpopo, 2011 / An experiment was conducted to determine the effect of egg weight on hatchability, hatch-weight and subsequent productivity of Venda chickens. A total of 360 Venda chicken eggs based on their weights were collected within one week and assigned to four treatments with five replicates of 18 eggs per replicate. A randomized design was used. The four treatment weights were below 49 g, between 50 and 59 g, between 60 and 69 g and above 70 g. the eggs were incubated for 21 days. The chicks were raised up to 13 weeks based on their treatments but fed a similar diet. Egg weight was positively and strongly correlated (r2 = 0.727) with hatchability. Similarly, egg weight was positively and strongly correlated (r2 = 0.0.953) with chick hatch-weight. Between one and seven weeks old, Venda chicks hatched from heavier eggs ate less (P< 0.05) than those hatched from lighter eggs. Heavier eggs hatched chicks with better (P< 0.05) feed conversion ratio. However, chicks hatched from heavier eggs tended to have higher (P< 0.05) live weight at seven weeks old than those hatched from lighter eggs. Heavier eggs tended to hatch chicks that had higher (P< 0.05) mortality rates. However, metabolisable energy and nitrogen retention of the chicks aged seven weeks was not (P> 0.05) affected by egg weight. Growth rate and live weight of the chicks aged between one and seven weeks were optimized at different Venda chicken egg weights of 56 (r2 = 0.514) and 60 (r2 = 0.870) g, respectively. Egg weight had no (P> 0.05) effect on metabolisable energy, feed conversion ratio, growth rate, live weight, carcass weight and carcass parts of Venda chickens aged between eight and 13 weeks except fat pad weight. Venda chickens hatched from lighter eggs had lower (P< 0.05) fat pad weights than those hatched from heavier eggs. Meat samples of chickens hatched from lighter eggs had higher (P< 0.05) nitrogen contents. It is concluded that Venda chicken egg weight affects (P< 0.05) egg hatchability, chick hatch-weight, growth rate, live weight and carcass characteristics of the chicken. However, these variables are optimized at different egg weights. This has implications on selecting eggs for incubation.

Thesis (M.Sc. (Animal Production)) --University of Limpopo, 2011 / Crossbreeding is one of the tools for exploiting genetic variation. The main purpose of crossing chickens is to produce superior crosses (i.e. make use of hybrid vigor), improve fitness and fertility traits.This study was carried out at the University of Limpopo Experimental Farm located in Limpopo, South Africa. The objective of the study was to evaluate the growth performance of differentpurebred and crossbred chicken genotypes. A 3 x 3 complete diallel mating system involving two indigenous breeds namely Venda (V) and Naked Neck (N) and one commercial broiler breed, Ross 308 (R), were used to produce three purebred (V x V, N x N, R x R), three crossbreds (R x V, R x N, V x N) and three reciprocals (V x R, N x R, N x V).The nine genetic groups were rearedfrom hatch to 13 weeks of age in a deep litter open house. Body weights of 180 chicks (20 chicks per genetic group), recorded at 0, 3, 5, 7, 9, 11, and 13 weeks of age, were used to estimate heterosis, general (GCA) and specific (SCA) combining abilities, maternal ability and reciprocal or sex-linked effects on body weights. Results showed that the Ross 308 had the heaviest body weight at all weeks of measurement except for hatch. With respect to crosses, the reciprocal V x R and the cross R x V had the heaviest body weights at 13 weeks (2448.40 and 2131.50 grams, respectively), although N x R had heavier body weight than R x V at all weeks of measurement except for hatch and 13th week. Results of heterosis estimates indicated that crossing between Venda male and Ross 308 female as well as between the Venda male and Naked Neck femalegave the highest heterotic effects for body weight(11.01% and 10.33%, respectively).General Combining Ability was significant (P≤0.01) for body weight from hatch to 13 weeks of age while SCA and Reciprocal effects (RE) were both significant (P≤0.05) for body weight at all ages of measurement except for hatch weight. The Ross 308 chicken gave the highest positive effect of GCA for body weight except for hatch weight. Venda sire crossed with Naked Neck dams gave the highest and positive effects of SCA for body weight. Naked Neck sire crossed with Venda dams had the highest positive estimate of RE for body weight except for the 13th week. Results show that using Venda chickens as a paternal breed in crossing with Naked Neck and Ross 308 females may improve growth performance of indigenous chickens.

This study was conducted to determine the effect of egg weight on hatchability and chick hatch-weight of Cobb 500 broiler chickens. A total of 396 Cobb 500 hatchable eggs classified according to three different egg weight groups as small: (<49 g) medium: (50-59 g) and large: (60-69 g) were used in the experiment. A complete randomized design of three treatments with three replicates and each replicate having” 44 eggs was used for the experiment. Simultaneously a linear type equation was used to determine the relationship between egg size and responses in hatchability values and chick hatch-weight. Results indicated that large-sized eggs produced chicks with higher (P<0.05) hatch-weight than medium and small-sized eggs. However, no differences were detected with fertility rate percentage, hatchability percentage and percentage hatch of fertile. It was therefore concluded from the result of the present study that sorting of Cobb 500 broiler chicken breeder eggs by weight prior to incubation might be advantageous in producing uniform size Cobb 500 broiler chicken hatchlings to meet specific market demands with improved efficiency. / Agriculture and  Animal Health / M. Sc. (Agriculture)

Thesis (M.Sc. (Animal production)) --University of Limpopo, 2011 / A study was conducted to examine the effect of protein level of the diet of Naked neck hens on egg production, hatchability and chick productivity. The first part of the experiment determined the effect of protein level on feed intake, number of eggs produced, egg weight, egg white nitrogen content, egg yolk nitrogen content, egg hatchability and chick hatch-weight. A total of 25 hens aged 30 weeks were confined in cages and fed diets differing in protein content. A complete randomized design, comprising of diets differing in protein levels (P12.94%, P13.94%, P14.38%, P15.75% and P18.13% CP), replicated five times with one hen in each replicate was used. Semen was collected from one cock to fertilize all hens. Protein level had an effect on (P<0.05) feed intake and egg white nitrogen content. However, protein level of the diet of hens had no effect(P>0.05) on the number of eggs produced, egg white nitrogen content, egg yolk,egg weight, egg hatchability and chick hatch-weight. Quadratic analyses indicated that feed intake, number of eggs produced, egg weight, egg white nitrogen content, egg yolk nitrogen content, hatchability and chick hatch-weight were optimized at different protein levels of 14.7 (r2 = 0. 623),14.9 (r2 = 0.568),13.9 (r2 = 0.094), 18.2 (r2 = 0.563), 15.1(r2 = 0.424), 15.9 (r2 = 0.451) and 15.9 %(r2 = 0.898) , respectively. The second part of the experiment determined the effect of protein level of hens on productivity of their progenies from a day old up to 13 weeks of age. A total of 95 chicks hatched from the first part of the study were assigned to 20 floor pens according to the number of chicks hatched. Chicks had an average initial live weight of 35 ± 2 g per bird. The chicks were fed the same commercial grower diet and fresh water ad libitum up to seven weeks of age. Protein level of the diet of Naked neck hens had an effect (P<0.05) on feed intake, live weight and feed conversion ratio of chicks from a day old up to seven weeks of age. However, protein level of the diet of Naked neck hens had no effect (P>0.05) on growth rate and mortality of chickens from a day old to seven weeks of age. Feed intake, feed conversion ratio, growth rate and mortality of chickens were optimized atdifferent protein levels of 15.8 (r2 = 0.298), 16.1 (r2 = 0.236), 16.1 (r2 = 0.077) and 14.3 % (r2 = 0.617), respectively. Protein level of the diet of Naked neck hens had no effect (P>0.05) on feed intake, growth rate and feed conversion ratio of both their male and female progenies between eight and 13 weeks of age. Protein levels of the diet of hens had an effect (P<0.05) live weight of their male progenies and carcass weights of both their male and female progenies at 13 weeks of age. However, the level of protein of the diet of hens had no effect (P>0.05) on live weight of their male progenies, and breast meat yield, breast meat nitrogen content and fat pad weight of both their male and female progenies at 13 weeks of age. Live weight,breast meat yield, breast meat nitrogen content and fat pad weight of their male progenies at 13 weeks of age were optimized at different protein levels of the diets of hens of 18.9 (r2 = 0.666), 15.6 (r2 = 0.081), 15.4 (r2 = 0.786) and 17.7 %(r2 = 0.775), respectively. Similarly, live weight, carcass weight, breast meat yield, breast meat nitrogen content and fat pad weight of their female progenies at 13 weeks of age were optimized at different protein levels of 15.7 (r2 = 0.294),15.4 (r2 = 0.180), 15.8 (r2 = 0.059), 15.1 (r2 = 0.882) and 16.1 % (r2 = 0.405), respectively. It is concluded that protein level of the diet of the hen may affect its productivity and that of its progeny. However, the calculated protein levels for optimum productivity will depend on the production parameter in question. / National Research Foundation

This study was conducted to determine the effect of egg weight on hatchability and chick hatch-weight of Cobb 500 broiler chickens. A total of 396 Cobb 500 hatchable eggs classified according to three different egg weight groups as small: (<49 g) medium: (50-59 g) and large: (60-69 g) were used in the experiment. A complete randomized design of three treatments with three replicates and each replicate having” 44 eggs was used for the experiment. Simultaneously a linear type equation was used to determine the relationship between egg size and responses in hatchability values and chick hatch-weight. Results indicated that large-sized eggs produced chicks with higher (P<0.05) hatch-weight than medium and small-sized eggs. However, no differences were detected with fertility rate percentage, hatchability percentage and percentage hatch of fertile. It was therefore concluded from the result of the present study that sorting of Cobb 500 broiler chicken breeder eggs by weight prior to incubation might be advantageous in producing uniform size Cobb 500 broiler chicken hatchlings to meet specific market demands with improved efficiency. / Agriculture and  Animal Health / M. Sc. (Agriculture)