Browsing by Author "Lwelamira, James"

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Genetic determination of immune responses to Newcastle disease virus vaccine in chickens
(Sokoine University of Agriculture, 2002) Lwelamira, James
A study was conducted at Sokoine University of Agriculture to investigate the genetic control of immune response of chickens against Newcastle disease virus (NOV) vaccine. The study involved local chickens from Tanzania (LL), Rhode Island Red derivative hybrids (EE), and their reciprocal crosses (LE and EL). The local ecotype had the highest mean antibody titres following primary vaccination, as well as before (residual) and after secondary vaccination, while the exotic breed had the lowest titres in all three measurements. The crossbred chicks were found to be intermediate between the two parental genotypes, but the differences between the local ecotype and the crosses were not significant except for the primary vaccination antibody titre. Furthermore, there were no significant differences between the reciprocal crosses. Differences between sexes were not significant. Despite the observed superiority of the local ecotype for antibody titre, there were no significant differences among genotypes with respect to mortality rate. Heritability estimates for antibody titre ranged from 0.27 ± 0.06 to 0.39 ± 0.09, 0.17 ± 0.03 to 0.32 ± 0.11, and 0.18 ± 0.08 to 0.28 ± 0.08 for antibody titre following primary vaccination, before, and after secondary vaccination, respectively. While the contribution of additive breed merit and heterosis effects in antibody titre before and after secondary vaccination were both significant, only the contribution of additive breed merits were significant for primary immune response. There were no significant correlation coefficients between antibody titres at different periods of measurement, nor between antibody titres and body weights. It was concluded that substantial improvement in immunological status of a stock against Newcastle disease could be achieved through both selection and crossbreeding
Prospects for improving performance of two Tanzanian chicken ecotypes through selection
(Sokoine University of Agriculture, 2007) Lwelamira, James
A study was carried out to evaluate the possibility of improving the performance among two chicken ecotypes of Tanzania viz. Kuchi and Tanzania Medium through selection. The study involved evaluation of their genetic potential, estimation of genetic parameters for various traits, and determining optimal breeding strategies for their improvement through selection, furthermore, prospects for using Marker Assisted Selection (MAS) for some trails were also investigated. Results indicated that Kuchi had significantly higher body weights (l’< 0.001), better feed conversion ratio (P<0.05), and laid eggs with higher weights (P< 0.05) than Medium ecotype. On the other hand. Medium ecotype was superior in terms of egg production and attained sexual maturity earlier than Kuchi (P< 0.05). However, differences between ecotypes with respect to other egg quality traits and primary antibody response (primary humoral immune response) against Newcastle disease virus (NDV) vaccine were not significant (P> 0.'05). Moderate to high hcritability estimates were obtained for various trails in both ecotypes. 1 he estimates varied from 0.22 to 0.53 fbr Kuchi, and 0.23 to 0.61 for Medium ecotype. with most of the corresponding estimates between the two ecotypes being close to each other. Genetic (rg) and phenotypic (rp) correlations in both ecotypes were highest among body weights (i.c. rg = 0.60 to 0.93 and rp = 0.54 to 0.78; rg = 0.53 to 0.80 and rp= 0.44 to 0.72. under intensive and extensive management systems, respectively), and were lowest (i.e. around 0.10 and below, ranging from negative to positive) among primary antibody response against NDV" vaccine and production trails, and among eggshell thickness, egg shape index and other production traits. The magnitude of- herilability estimates obtained in this study permit improvement of performance of these ecotypes through selection. As Kuchi chickens were shown to be superior to Medium ecotype in terms of body weight, and converse was true foregg production. Therefore, it was recommended to put emphasis for further improvement in body weights in Kuchi, and egg production in Medium ecotype. Depending on a breeding scenario, results from simulation studies indicated that it w'ould take between 5 to I I generations of selection for achieving pre-defined desired gains in various trails. The corresponding years of selection varied from 3 to 12 years. There were some LEI0258 microsatcllitc alleles (a microsatellile located within MHC B region) which had significant effect on primary antibody response against NDV vaccine (alleles of 205 and 307bp) and body weight (allele of 307bp), hence showing good prospects for using MAS for further improvement of these trails.