Inbreeding coefficient and its effect on performance of cocoon traits in four Iraniancommercial silkworm lines

摘要

Increase of inbreeding could cause reduction in performance of some economic traits of animal populations. Thereby in line breeding there is an attempt for prevention of more inbreeding in populations. The level of inbreeding and its relationship to the economic traits (cocoon weight, cocoon shell weight and cocoon shell percentage) of 4 lines of Iranian silkworm populations (107 and 153 of Japanese origin and 110 and 154 of Chinese origin) using 3 regression models were estimated. In the first modellinear effect of inbreeding, in the second model linear and quadratic effect of inbreeding and in the third model linear, quadratic and cubic effect of inbreeding on the traits were investigated with presence of line, family and gender effects. Pedigreeinformation of 40,717 silkworms collected during 9 generations during 2001-2006 in Iran Silkworm Research Center were studied. The average of inbreeding coefficient of total population was 9.626%. Except for line 153 in the second model and line 107 inthe third model, inbreeding had positive effect on cocoon shell percentage. Model 1 with linear inbreeding effect had more significancy (p<0.0001) and less complexity for study of inbreeding effect on cocoon shell percentage. On the basis of Model 1, inall studied lines, except for line 154, inbreeding effect on cocoon weight and cocoon shell weight was not significant. On the basis of Model 3, inbreeding had negative effect on cocoon weight and cocoon shell weight in line 110. The estimates of inbreeding effect on studied traits was intensively affected by the type of statistical model.