Studies on Inbreeding Depression in Japanese Quail

Abstract

Successive full-sib matings of Japanese quail were originated from forty pairs of twenty eight lines obtained by crossing males introduced from a quail-breeder in Toyohashi to random bred females propagated in our Laboratory. The inbred populations were reproduced by five hatches of five week's eggs layed by the parental quails when they were nine to twelve weeks of age. Those hatched birds were pooled and paired for full-sib mating. Inbreeding depressions of various characters were studied by weighted regression, and the genetic load was estimated.1) Regression coefficients for both fertility and hatchability on inbreeding coefficient were nagative and significant. Tendencies of depression in viability up to four weeks of age, sexual maturity, body weight at sixteen weeks, egg production to sixteen weeks and egg weight at thirteen weeks were observed, but the regression coefficients were not significant because of small degrees of freedom.2) Owing to severe inbreeding depression, successive full-sib matings were encountered with serious difficulty of reproduction by the fifth generation.3) The estimated number of lethal equivalents per bird for fertility, hatchability and viability to four weeks were 1.0, 2.5, and 1.5, respectively. Therefore, the total number of detrimentals for each quil was 4.9. Those value estimated in the inbred lines of S, H, M and J were 2.3, 13.0, 24.3 and 10.6, respectively. The differences in the lethal equivalents among those inbred lines were not significant. It is suggested that the genes responsible for the detrimental load in the quail have overdominant effects, since the ratio B/A is relatively low (3.2).