Ornithine decarboxylase (ODC) is the rate determining enzyme in the biosynthesis of polyamines which are essential for cell growth. In chickens, significantly higher bioactivity is reported in broiler than in egg layer strains of chickens (Bulfield et al., 1988). To characterize the genetic differences in growth rates and ODC levels in chickens, an ODC cDNA and genomic gene were cloned and sequenced. Sequencing of ODC cDNA revealed that this clone (pODZ3: 2,052 bp) was not a full length of ODC cDNA and contained 2 putative introns. The open reading frame (introns deleted) coded for a protein of 404 amino acids which had about 85% amino acid identity with human ODC. Sequencing of genomic ODC clone (pODG2-8: 5098 bp) represented the 3$ prime$ end of ODC gene from downstream of intron 7. Northern blotting of chicken RNA probed with the insert of pODZ3 revealed 2 hybridizable messages of 1.6 and 2.1 kb, respectively. In addition, analysis of MspI restriction fragment length polymorphism (RFLP) using the 3$ prime$ end of ODC gene as a probe suggested that two MspI RFLPs present in the lean line of broiler chickens was related to selection of high lean body mass.

No description available.

Five experiments were conducted to study genetic influences on growth and early egg production in chickens. Parental lines included White Plymouth Rocks divergently selected 25 generations for high (H) and for low (L) 56-day body weight and a closed population of Jersey Black Giants (JJ). F₁ generation crosses (sire listed first) included HL, LH, JL, and JH, and an F₂ generation from HL x HL matings. Comparisons also include dwarf and nondwarf chickens from the H and L lines. Symbols for dwarfs and nondwarfs within the high line were HD and HN and within the low line were LD and LN. Growth patterns of dwarfs more closely approximated that of the H than that of the L line, regardless of whether measured in a chronological or physiological context. Although body components were usually smaller for dwarfs than their within-line nondwarf counterparts, on a relative body weight basis, dwarfs were more uniform than nondwarfs. Dwarfs were also more uniform than normals for age at first egg. The dw allele reduced yolk formation and ovulation rate, resulting in less erratic ovulation and lowering the incidence of defective eggs. Differences between reciprocal crosses were minor as were recombination effects for the traits measured. There was little, if any, evidence of heterosis for body weight and skeletal and lean traits prior to 57 days of age, at sexual maturity, or 60 days after the onset of lay. When present, heterosis was general for most traits measured with the exception of those associated with adiposity which were population dependent. Modest heterosis was observed for the age of inflection of the growth curve, age at sexual maturity, egg production traits, and body weight change during a 60-day laying period. Hybrid vigor for egg production traits resulted in more normal eggs via regularity of yolk development and synchronization of ovulation. The onset of sexual maturity was accompanied by the achievement of a population-dependent body composition, which was generally independent of age and body weight. Under ad libitum feeding, lean carcass traits appeared to be more critical to the onset of sexual maturity than adiposity, as evidenced by greater differences between mature and immature pullets for the former than for the latter traits. The exception to this pattern was the line selected for low juvenile body weight where adiposity traits appeared to be primary. / Ph. D.

Genetic and nongenetic influences on organ development in chickens were studied. Populations included lines divergently selected for juvenile body weight, reciprocal F₁ crosses between them, and a commercial broiler-breeder parent line segregating for early and late feathering alleles. Nongenetic influences included restricted and <i>ad libitum</i> (AL) feeding regimes. Positive correlated responses to selection for body weight included proportionally larger breast, legs, fat depots and small intestine. Negative responses included fecundity, feather and gizzard weights. The degree of non-additive genetic variation differed among traits but reciprocal effects were negligible. Weights and lengths of organs at specific ages did not necessarily reflect the situation at common body weights suggesting differences in resource allocations among populations. In commercial meat-type chickens, AL feed consumption was near gut capacity and increased rapidly to approximately 140 days of age. Concomitantly, body weights increased to approximately 130 days and then plateaued. Influences of early and late feathering alleles were minor except for weights of feathers. Alternate-day feeding prior to sexual maturity reduced weights of fat depots, feathers and muscles and increased size of the gastrointestinal tract. Effects of every day, skip-one-day and skip-two-day restrictions of feed were generally similar. Chickens adapted quickly to restricted feeding but, when released to AL feeding allocated resources into growth. This reallocation reduced their resistance to an <i>Escherichia coli</i>challenge. Prior to sexual maturity, relative weights and lengths of the gastrointestinal tract decreased with age and relative sizes of fat depots and muscle increased with age. Thereafter relationships of most organs to body weight remained stable. Restricted chickens adapted to fasts by maintaining exogenous energy stores (gastrointestinal tract contents) for longer periods. Unlike those fed AL, they did not became obese and their livability and fecundity were greatly enhanced. / Ph. D.

Typescripe (photocopy). / Digitized by Kansas Correctional Industries

Thesis (PhD (Animal Sciences))--Stellenbosch University, 2011. / ENGLISH ABSTRACT: The current study was undertaken to determine the effectiveness of the current South African chicken conservation programmes in conserving the genetic diversity of village chicken populations. Village chicken farmer’s production constraints such as feed availability, chicken mortality, prevalence of diseases and chicken sales were influenced by gender, age, wealth status, production system, chicken flock size, type of chicken breed owned, accessibility of veterinary services, availability of supplements, vaccines and shelter. Considerable phenotypic heterogeneity in qualitative traits of indigenous chicken populations and their distributions in different regions of South Africa revealed the absence of selection on a preferred phenotype, showing that the population is not standardized. Genetic diversity studies using both microsatellites and mtDNA markers demonstrated that the conservation flocks of South African chickens displayed considerable genetic variability that is different from that of the assumed founder populations (field chicken populations). The indigenous chicken mtDNA further revealed multiple maternal lineages in South African chickens, where conservation flocks and field chicken populations shared these major haplotypes A, D and E which are presumed to be of Chinese, South East Asia and Indian subcontinent origin, respectively. The overall findings of the study increased awareness of the importance of genetic management and utilization of indigenous chicken genetic resources of South Africa. As a result, the study provides a base-line dataset to complement the decision-making process on designing proper conservation strategies for South African indigenous chicken genetic resources. / AFRIKAANSE OPSOMMING: Die huidige studie is onderneem om die doeltreffendheid van die Suid-Afrikaanse hoenderbewarings programme in die bewaring van genetiese diversiteit in dorphoender bevolkings. Dorp hoenderboere se produksie beperkinge soos voerbeskikbaarheid, hoender mortaliteit, die voorkoms van siektes en hoenderverkope word beïnvloed deur geslag, ouderdom, rykdom status, produksie sisteem, hoender kudde grootte, tipe hoenderras, toegang tot veeartsenydienste, beskikbaarheid van supplemente, inentstowwe en skuiling. Merkbare fenotipiese variasie in kwalitatiewe eienskappe van die inheemse hoenderbevolking en hul verspreiding in verskillende areas van Suid-Afrika, is aanduidend dat daar nie seleksie plaasvind vir ‘n voorkeur fenotipe nie, wat dus toon dat die bevolking nie gestandardiseer is nie. Genetiese diversiteit studies met behulp van beide mikrosatelliete en mtDNA merkers het getoon dat die bewaringskuddes van Suid- Afrikaanse hoenders vertoon merkbare genetiese variasie wat verskil van die veronderstelde stigter bevolkings (veldhoender populasies). Die inheemse hoenders mtDNA het verder onthul dat verskeie moederlike afstammelinge in die Suid Afrikaanse hoenders, major haplotipes A, D, E wat afkomstig is vanaf die Chinese, Suid-Oos Asië en die Indiese subkontitent onderskeidelik; gedeel word saam met die bewaringskuddes en die veldhoender populasie. Die algemene bevindige van die studie verhoog die bewustheid van die belangrikheid van genetiese bestuur en benutting van inheemse hoender genetiese hulpbronne van Suid-Afrika. As gevolg hiervan, verskaf die studie ‘n basis-lyn datastel vir die besluitnemingproses oor die ontwerp van ‘n ordentlike bewaring strategieë vir die Suid-Afrikaanse inheemse hoender genetiese hulpbronne.

Production traits and disease resistance are believed to be under the control of many genes, i.e. quantitative trait loci (QTL). The objective of the present study was to establish a methodology for identifying DNA markers which are associated with QTL in chickens using an alternative approach to the traditional linkage analysis. A systematic screening approach was designed to search a chicken liver cDNA library for clones which revealed polymorphisms associated with traits. In the first stage of the experiment, a total of 92 cDNA clones were subjected to restriction fragment length polymorphism (RFLP) analysis. About 33% and 22% of the clones revealed DNA polymorphisms at MspI and TaqI restriction sites, respectively. Subsequently, DNA polymorphisms which responded to selection were identified by comparing RFLP frequencies in divergently selected strains of chickens. About 60% of the RFLPs responded to selection for egg production traits and/or Marek's disease (MD) resistance. Trait associations of these RFLPs were then studied by selectively genotyping individuals at the extremes of trait distributions, followed by an analysis of individuals in the entire population and statistical evaluation. Finally, RFLP regions of DNA markers were characterized and PCR assays for rapid RFLP screening were developed. DNA markers in two genes were identified and characterized by this methodology. One was a marker in the chicken mitochondrial genome which arose from a nucleotide substitution (T to C) in the NADH subunit IV gene. Statistical analysis for typing random individual samples from the strains showed that this DNA polymorphism was associated with mature body weight and egg specific gravity which is a strong indicator for egg shell thickness. Other analyzed markers were located in the chicken mitochondrial phospho-enolpyruvate carboxykinase (PEPCK-M). Using the cDNA of this gene as a probe, southern blotting revealed a highly polymorphic band pattern. Statistical analy

Diss. (sammanfattning). Swedish University of Agricultural Sciences : Sveriges lantbruksuniv. / Härtill 5 uppsatser.

No description available.

The experiments reported in this dissertation explored the effects of selection for antibody response on other immunological measures and on production traits. The role of thyroid hormones in antibody response was also studied. Selection for high (HA) and low (LA) antibody response to sheep erythrocytes altered subclasses of antibodies in different ways. In line LA antibody response was primarily mercaptoethanol-susceptible (IgM), while the line HA response was primarily mercaptoethanol-resistant antibody (IgG). Sublines of HA and LA were developed with all possible combinations of major histocompatibility complex haplotypes B¹³ and B²¹. An experiment was conducted to test Marek’s disease resistance of these haplotypes in line LA. Mortality from a natural exposure was high for all three groups, and there was no difference among haplotypes. Correlated responses of growth and reproductive traits in lines HA and LA were due to genetic correlations with antibody response. These genetic correlations were generally negative and are suggestive of differential allocation of resources. Phenotypic correlations were generally very small. Changes in allelic frequencies at alloantigen systems were also observed in response to selection. Experiments designed to study the role of thyroid hormones on antibody responses showed no direct relationship. Chickens from lines HA and LA fed thiouracil exhibited hypothyroidism but did not differ from controls in antibody response. Differences in thyroid hormone concentrations between lines of dwarf and non-dwarf White Rocks selected for high and low juvenile body weight bore no relationship to differences in antibody responses. / Ph. D.