# Heritability and Genetic Correlation of Age at First Egg and Egg Number up to 40 Weeks of Age After Long-Term Selection in Taiwan Indigenous Chicken

## TL;DR

This study estimates genetic parameters of egg-laying traits in four lines of Taiwan indigenous chickens after long-term selection.

## Contribution

The study provides updated heritability and genetic correlation estimates for egg-laying traits across generational stages in four chicken lines.

## Key findings

- Heritability estimates varied across traits and generational stages, with Gain40 and EW40 showing less fluctuation.
- Favorable negative genetic correlations between age at first egg and egg number were observed in the final generational stage.
- The results suggest potential for improving breeding programs for egg production in these chicken lines.

## Abstract

We estimated the genetic parameters of egg-laying-related traits in different generational stages of four Taiwan indigenous chicken lines. All four lines were derived from in situ conservation populations of the National Livestock Biodiversity Program and had undergone long-term selection for egg-laying traits since 1987. The results showed that the estimated genetic parameters of the investigated traits fluctuated among the generational stages, and the extent of fluctuation varied by line. The heritability and correlation estimates of the traits of the final stage of the selected generations suggest that the sustainability of breeding programs and the selection of the four traits from this study can still be improved.

The objective of this study was to estimate the genetic parameters of the egg-laying traits of hens after long-term selection. Four lines were derived from Taiwan indigenous chickens conserved in situ by the National Livestock Biodiversity Program. A total of 9834 hens’ laying records from 18 non-overlapping generations classified as seven generational stages from 2006 to 2023 was used. The traits evaluated included body weight at 16 weeks of age, age at the first egg (Sday), body weight change between Sday and 40 weeks of age (Gain40), mean egg weight at 40 weeks of age (EW40), and egg number up to 40 weeks of age (EN40). A four-trait animal model via the REML procedure was used to estimate the variance/covariance components for each generational stage within each line. The ranges of the heritability estimates for Sday, Gain40, EW40, and EN40 were 0.09–0.61, 0.03–0.70, 0.32–0.83, and 0.00–0.65, respectively. Within the lines’ generational stages, most of the heritability estimates of Gain40 and EW40 were higher than those of Sday and EN40. Also, less fluctuation was found in the heritability estimates of Gain40 and EW40 among the generational stages within the lines. Favorable negative genetic and phenotypic correlations between Sday and EN40 were observed at the last generational stage, which could be beneficial for future breeding programs to improve egg production.