Abstract
Reproduction performance of 21 inbred experimental lines of White Leghorns was evaluated based on samples of reproduction records over a period of eight consecutive years. Two lines (63 and 72) have been extensively used in studies, especially in research seeking for genetic and epigenetic factors underlying resistance to avian tumor virus-induced diseases in chickens. The other 19 lines are recombinant congenic strains (RCS), which were generated by crossing lines 63 and 72 followed by two consecutive backcrosses to the line 63 and then full-sib mating. In theory, each RCS processes 7/8 of progenitor background line 63 genome and a random sample (1/8) of the progenitor donor line 72 genome. All 21 inbred lines share a common major histocompatibility complex haplotype, B*2. The estimated average fertility of the 21 inbred lines ranged from 72.9% (RCS-J) up to 96.8% (RCS-P). Both progenitor lines 63 and 72 were observed with lower average fertility (82.4% and 81.6%, respectively) in comparison with the RCS except the RCS-J, suggesting a substantial polygenic component underlying the fertility phenotype. The average embryo mortality rate ranged from 14.5% (RCS-P) up to 47.0% (RCS-M). The background line 63 fell at about the middle of the range (28.3%) significantly higher than the donor line 72 (15.7%), which was among the group with the lowest embryo mortality. By definition, hatchability of fertile eggs is reversely correlated with embryo mortality. The average hatchability ranged from 26.5% (RCS-M) up to 66.8% (line 72) while the background line 63 remained (46.6%) at about the middle of the range. The variability of the average embryo mortality and hatchability observed among the 21 inbred lines indicated the two correlated traits also follow polygenic models of inheritance. Findings from this study paves the way for further investigation on genetic and environmental influence over reproductive performance of inbred lines of chickens, and particularly in understanding and improving the reproduction fitness of invaluable genetic resources like these inbred lines.
Highlights
Reproduction characteristics are of profound importance for livestock and poultry both in evolutionary and economic perspectives
Findings from this study paves the way for further investigation on genetic and environmental influence over reproductive performance of inbred lines of chickens, and in understanding and improving the reproduction fitness of invaluable genetic resources like these inbred lines
Since the foundations for genetic improvement were laid by Robert Bakewell in the 18th century [6], a variety of ways to employ inbreeding in combination with intensive selection to achieve breeding goals has been attempted
Summary
Reproduction characteristics are of profound importance for livestock and poultry both in evolutionary and economic perspectives. Fertility and hatchability are major parameters of reproductive performance for egg-layer type of chickens. The heritability estimates for fertility, embryo mortality, and hatchability of fertile eggs in chickens reportedly range from 0.05 to 0.13, which indicate these important traits bear heavy influence from management measures, nutrient supplies, and surrounding environmental conditions [1]-[5]. The adverse effects of inbreeding, commonly referred to as inbreeding depression, are richly documented. In poultry, inbreeding depression adversely affect production performance, and reproductive characteristics, including fertility, embryo mortality, and hatchability [7]-[13]
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