Estimation of inbreeding depression for growth and production traits in native chicken using quantile regression

The aim was to estimate the inbreeding coefficient and its impact on important economic traits in Yazd native fowls breeding station by quantile regression. Therefore, 57400 data collected from 2001 to 2017 (15 generations) was used. Traits included body weight at hatch (BW1), the 8th (BW8) and 12th week (BW12), age and weight at sex maturity (ASM, WSM), the egg number (12 weeks of production) (EN), average egg weight (28th, 30th, 32th weeks of production) and the first egg weight (EW1). Data was edited by Foxpro and estimation of inbreeding coefficient was computed by CFC. The regression coefficient of inbreeding was fitted on generation by linear regression of Rsoftware. Impact of inbreeding on traits was investigated by quantile regression. The fixed effects in the models were sex, hatch number, generation and inbreeding depression was considered as covariate. Pedigree analysis showed that 79percent of population were inbred and average of individual inbreeding coefficient was %3. The slope trend of individual inbreeding was increased by 0.5 percent on generation. Exploring different trait quantile distributions, it was revealed that inbreeding depression had different impacts over range of its distribution in a way that a much pronounced effect was observed in extremes (25%, 75%).Quantile regression was not converged for BW1, ASM and EW1 and they were estimated by linear regression as 0.001, 0.053 and 0.063,respectively. According to quantile regression, the impact of inbreeding depression was not equal on different parts of traits' distribution, which give us a better insight of the effect of inbreeding.