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Evaluation of reproductive characteristics of 21 highly inbred lines of White Leghorns divergently selected for or segregating in tumor resistance

Gururaj Kulkarni, Huanmin Zhang
Open journal of animal sciences 2015 v.5 no.1 pp. 59-70
White Leghorn, backcrossing, chickens, disease resistance, egg hatchability, eggs, embryonic mortality, epigenetics, haplotypes, inbred lines, major histocompatibility complex, models, mortality, neoplasms, phenotype, reproductive performance, research projects
Reproduction performances of 21 inbred experimental lines of White Leghorns were evaluated based on samples of reproduction records over a period of eight consecutive years. Two of the lines (line 63 and line 72) are highly inbred and have been extensively used in many research projects, especially in research seeking for genetic and epigenetic factors underlying resistance to avian tumor virus-induced diseases in chickens. The other 19 lines are known as recombinant congenic strains (RCS), which were generated by crossing the lines 63 and 72 followed by two consecutive backcrosses to the line 63 and then full-sib mating to establish each RCS. In theory, each RCS maintains 7/8 of genome contents of the progenitor background line 63 while received a random sample 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 percent (RCS-P). Both progenitor lines 63 and 72 were observed with lower average fertility (82.4 and 81.6 percent, 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) percent. The background line 63 fell at about the middle of the range (28.3 percent) significantly higher than the donor line 72 (15.7 percent), which was among the group with the lowest embryo mortality. By definitions, 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) percent while the background line 63 remained (46.6 percent) 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.