Genetic Evaluation of the Effects of Divergent Feathering Selection and Major Feathering Genes on Growth Performances and Carcass Traits in Broiler Chickens

Lou, Mengliang (1994) Genetic Evaluation of the Effects of Divergent Feathering Selection and Major Feathering Genes on Growth Performances and Carcass Traits in Broiler Chickens. PhD thesis, University of Glasgow.

Abstract

The general objectives of the research undertaken were firstly to demonstrate the possibilities in feathering manipulation of chicks by means of quantitative feathering selection or by means of introducing major genes, and secondly to elucidate the consequences of different methods of genetic feathering manipulation for broiler production. With these, a divergent feathering selection program has been proceeded to the eighth generation. The breeders in different generations were used in various matings with other lines carrying different major feathering genes. The chicks so produced were tested in the series experiments for the feathering measurements, broiler growth performance, carcass traits and body protein partition. The tail feather length and body weight data collected from eight generations of the fast and slow feathering selection were summarised for the direct response in feathering and correlated response in body weight to the feathering selection. In order to draw both the practical and theoretical implications from the selection program, these data were also subjected to the REML analyses. The variance and covariance components and genetic parameters were estimated both for the base population and later generations based on data from different lines and combinations of generations. The results obtained were: 1). Quantitative selection has been effective in manipulating the feathering trait. After eight generations of selection, the fast feathering line had a three-week tail feather length more than two times of that in the control line, and from four to five times that in the slow feathering line. 2) The base population had high heritabilities for both tail feather length and body weight. The combined estimates were 0.54 and 0.56 for the tail feather length, and 0.54 and 0.47 for body weight based on data of generations 1-2 and generations 1-3, respectively. Estimates for the later generations were lower, and were 0.32 and 0.33 for the tail feather length, and 0.51 and 0.35 for body weight with data including generations 4-8 and generations 6-8, respectively. 3) The control line had higher heritabilities for both of the traits than the selected lines in the later generations. Compared with the control, feathering selection reduced the genetic variance of this trait by about two thirds (23.5 vs. 7.57), after four rounds of intensive selection in the slow line, but not the fast line (21.9). 4). Treating parents without records as fixed effects might help to account the bias in heritability estimation caused by intensive selection before and within the assumed base generation. However, this option should be used with caution. 5) In the base population, the tail feather length had a moderate positive genetic correlation with body weight at 24/25 days (0.49, 0.48 and 0.35 for the data from the fast, control and slow feathering lines, respectively). This correlation could be reduced rapidly by random drift and especially directional selection. (Abstract shortened by ProQuest.).

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Additional Information: Adviser: W K Smith
• Keywords: Animal sciences
• Date of Award: 1994
• Depositing User: Enlighten Team
• Unique ID: glathesis:1994-74975
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 27 Sep 2019 14:49
• Last Modified: 27 Sep 2019 14:49
• URI: https://theses.gla.ac.uk/id/eprint/74975