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A Study on the Genetic Variability of Egg Production Traits in Taiwan Country Chicken
|關鍵字:||Taiwan Country Chicken;台灣土雞;Clutch;Genetic Variability;產蛋週期;遺傳變異||出版社:||畜產學系||摘要:||
Reproductive performance was one of the important economic traits in the breeder chickens. In general, Taiwan country chicken has showed a lower egg production as a result of a serious problem for egg production in the breeder. Selection for increase clutch length has achieved a significant improvement for egg production in layers. The purposes of this study were to estimate the genetic correlations between clutch traits and egg production in Taiwan country chicken. The data set was from the National Chung-Hsing University a long-term selection experiment, four strains B, S, D, and L2 that were from the same base population. Daily egg production and pedigree records of the last five generations were used to analyze. In order to satisfy the classical hypothesis for describing traits with polygenetic inheritance via a linear model with normal error, the Box-Cox transformation was used to normalize trait distribution. Variance and covariance components were estimated using VCE package.
1.Compare with egg production traits among the four strains
Total egg numbers to 40 wks of age was 71.7, 70.7, 59.4, and 50.7 for the L2, D, S and B strains, respectively. L2 strain had the longest average clutch length (4.07). S strain had the longest average pause length (4.42). The age at first egg is shorter in D strain (157.2), and B strain had the longest (175.5).
The coefficient of skewness and kurtosiss of non-normally distributed traits after the Box-Cox transformation were close to zero. After normality, the heritabilities of the most of traits were increased.
3.Estimation of genetic parameters for egg production traits
The results in comparison with heritability of egg production in Taiwan Country Chicken, in sire strains (B, S strain), the heritabilities of pause traits were higher than heritability of total egg number, in dam strains (D, L2 strain), the heritabilities of clutch traits were higher than heritability of total egg number. Genetic correlations between pause traits and the number of eggs laid to 40 weeks of age were higher among the four strains. Compare to egg number with the related selection traits, the pause traits were more relative efficiency in sire strains, and the clutch traits were more relative efficiency in dam strains.
In sire strains, heritabilities of pause traits deleting periods without laying egg for more than seven days were lower than those of undelete. In contrast, the heritabilities of pause traits exhibited a higher value in dam strains.
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