A comprehensive study on how inbreeding influences the growth and reproductive traits of six indigenous chicken breeds subjected to selection programmes

Indigenous chickens are a significant element of the farming system in rural areas of Iran. This study presents a systematic analysis of how inbreeding affects the growth and reproductive traits across six indigenous chicken breeds that are under genetic selection programmes. Pedigree data of 404,597 chickens from six indigenous chicken breeding centres were collected and analyzed over 15 to 29 generations. The study included eight production and reproduction traits. The results showed that the average inbreeding coefficient in the studied populations varied between 2.2% to 6.3% in centres. The average inbreeding rate was estimated to be between 0.3% and 0.6%, which is within the acceptable range for breeding programmes. Regression analysis of studied traits on inbreeding percentage showed that increased inbreeding had a slight negative effect on some traits, such that every 1% increase in inbreeding resulted in a decrease of 1.53 to 3.51g in body weight at 12 weeks and an increase of 0.12 to 0.38 days in age at sexual maturity. However, the effect of inbreeding on egg traits was insignificant. In conclusion, despite the implementation of a closed breeding system and genetic selection in centres, inbreeding has increased slowly in the populations, and genetic diversity has been maintained at an adequate level due to the successful implementation of selection and mating programmes running in indigenous chicken breeding centres.