Objective Calculate the genetic parameters and genetic gain of various growth and development traits of meat-type Xinjiang brown cattle (hereinafter referred to as meat-type brown cattle) at different stages, providing a reference for the subsequent updating and optimization of the selection index and breeding plan for meat-type brown cattle. The research subjects were 2486 meat-type brown cattle from three generations, and six traits including weight, height, body diagonal length, chest circumference, ultrasonic back fat thickness, and ultrasonic eye muscle area from birth to 24 months of age were collected.

Methods The AI module in the genetic evaluation software DMU was used, in conjunction with the AI-REML, EM algorithm, and a multi-trait animal model to estimate the variance-covariance components of the above traits and to estimate the genetic parameters.

Results The heritability (h²) of weight traits at different growth stages of meat-type brown cattle ranged from 0.13 to 0.56, height traits from 0.20 to 0.41, body diagonal length from 0.27 to 0.41, chest circumference from 0.10 to 0.42, ultrasonic back fat thickness from 0.12 to 0.62, and ultrasonic eye muscle area from 0.27 to 0.42. Phenotypic and genetic correlations of weight and body size traits at different growth and development stages were all positive, with ranges of 0.59～0.92 and 0.49～0.78, respectively. The correlations of ultrasonic back fat thickness and ultrasonic eye muscle area traits with other traits were weaker, with phenotypic correlation coefficients ranging from −0.12 to 0.37. This indicates that ultrasonic data need to be independently included in the selection index of meat-type brown cattle. At different growth and development stages, chest circumference showed a strong genetic or phenotypic correlation with weight, ranging from 0.78 to 0.90 and 0.87 to 0.92, respectively. At 24 months of age, there was a high genetic correlation between chest circumference and ultrasonic back fat thickness, with a correlation coefficient of 0.83. This indicates that chest circumference can be used as an indicator trait for weight and ultrasonic back fat thickness traits. The average genetic progress of weight traits from birth to 24 months of age in the three crossbreeding generations of meat-type brown cattle ranged from 0.34 to 6.43. The average genetic progress of height traits from 6 to 24 months of age ranged from 0.001 to 0.35, body diagonal length from 0.15 to 0.39, and chest circumference from 0.06 to 0.90. Relative to molecular breeding, the current genetic progress of conventional meat-type brown cattle is relatively slow.

Conclusion The heritability of body size and weight traits of meat-type brown cattle varies greatly at different growth stages, and this genetic difference should be fully considered when formulating selection indices and breeding plans. It was also found that ultrasonic traits need to be independently included in the selection index of meat-type brown cattle. When formulating the breeding plan for meat-type brown cattle, chest circumference can be considered as an auxiliary selection trait for weight and ultrasonic back fat thickness. Molecular breeding or bio-breeding techniques need to be introduced to further improve the selection efficiency of meat-type brown cattle.