# Genetic Evaluation of Early Growth Traits in Yunnan Semi-Fine Wool Sheep

## TL;DR

This study evaluates genetic and non-genetic factors affecting early growth in Yunnan semi-fine wool sheep to improve breeding strategies.

## Contribution

Identifies optimal genetic evaluation models and quantifies heritability for birth and weaning weights in a Chinese sheep breed.

## Key findings

- Birth year, dam age, sex, flock, and litter size significantly affect birth and weaning weights (p < 0.01).
- Heritability estimates for birth weight and weaning weight are 0.3123 and 0.3471, respectively.
- Farm location had no significant effect on either trait (p > 0.05).

## Abstract

The Yunnan semi-fine wool sheep is the first semi-fine wool sheep breed developed in China. This study investigates the non-genetic factors influencing early growth traits and estimates their genetic parameters, providing a scientific basis for the selective breeding of this breed and other semi-fine wool sheep populations. The findings indicate that birth year, dam age, sex, flock and litter size significantly affect Birth Weight (BWT) and Birth Weight (BWT) (p < 0.01). Additionally, birth month was found to significantly influence Birth Weight (BWT) (p < 0.01), while weaning month had a statistically significant effect on Weaning Weight (WWT) (p < 0.05). No significant effects of farm location were observed on either trait (p > 0.05). The most accurate genetic evaluation model determined the heritability of the Birth Weight (BWT) and Weaning Weight (WWT) as 0.3123 and 0.3471.

With economic development and improved living standards, the demand for mutton and wool continues to grow, and improving the production performance and genetic potential of sheep breeds has become the key to promoting the high-quality development of the sheep industry. Thus, this study analyzes the influencing factors of the early production traits of Yunnan semi-fine wool sheep, optimizes the genetic evaluation model, and relies on accurate genetic parameter estimation to provide a theoretical basis for formulating a scientific and efficient breeding strategy for this breed. Data were collected from the Laishishan and Xiaohai breeding farms in Qiaojia, Yunnan, covering production records of the core flock from 2018 to 2022. Using the GLM procedure in SAS 9.4 software, this study analyzed the non-genetic influences on early production traits in Yunnan semi-fine wool sheep. Concurrently, Danish Milk Unit 5 (DMU 5) software estimated the variance components across various animal models for each trait. Employing the Akaike Information Criterion (AIC) and likelihood ratio test (LRT), six models were tested, incorporating or excluding maternal inheritance and environmental impacts, to identify the optimal model for deriving the genetic parameters. The results show that the birth year, dam age, sex, flock and litter size significantly affect both the Birth Weight (BWT) and Weaning Weight (WWT) (p < 0.01). Additionally, the birth month was found to exert a significant effect on Birth Weight (BWT) (p < 0.01), the weaning month has a significant effect on the Weaning Weight (WWT) (p < 0.05). No significant effects of farm location were observed on either trait (p > 0.05). The most accurate genetic evaluation model determined the heritability of the Birth Weight (BWT) and Weaning Weight (WWT) as 0.3123 and 0.3471. From a production perspective, improving lamb birth, Weaning Weight (WWT), feed composition, and maternal nutrition during gestation is vital for breeding efficiency. This study not only identified the optimal animal models for early growth traits in Yunnan semi-fine wool sheep, offering a precise basis for estimating genetic parameters but also provides theoretical guidance for genetic selection and breed improvement in this population.