Co-variance component estimation for South African Hereford, Charolais, and Angus cattle for application in genetic evaluations

Abstract

This study developed (co)variance components and heritability estimates for growth traits in South African Angus, Charolais, and Hereford cattle, well-established breeds farmed locally for over a century. Genetic parameters are required for genetic evaluations. In this study genetic parameters were estimated for the specific populations by using single- and multi-trait models based on available data over 10-year (2012-2022) and 20-year (2002-2022) periods. Key traits analysed included birth weight, weaning weight, yearling weight, and 18-month weight, Average Daily Gain (ADG), hip height, body length and scrotal circumference. This study developed single and multi-trait models for (co)variance estimations. The single-trait models for Angus birth weight exhibited higher direct heritability estimates (0.41 to 0.49) compared to weaning weight (0.02 to 0.26), yearling weight (0.05 to 0.43), and 18-month weight (0.25 to 0.44) for the Angus breed. The Charolais exhibited similar results, and the Hereford estimates varied across the traits with large variability, birth weight (0.001 – 0.29), weaning weight (0.03 – 0.19), yearling weight (0.07 – 0.25) and 18-month weights (0.01 – 0.56). Single-trait models indicate the role of environmental effects such as inclusion of Sire by Herd (SXH) effects in breed models which raises residual variance, and the Permanent Environment (PE) effect which impacted traits from birth to 18 months, therefore they must be evaluated for inclusion. For Angus, multi-trait heritability estimates were (0.50 ± 0.02, 0.43 ± 0.02) for birth weight, (0.31 ± 0.24, 0.27 ± 0.02) for weaning weight, (0.50 ± 0.04, 0.36 ± 0.03) for yearling weight, and (0.35 ± 0.06, 0.39 ± 0.03) for 18-month weight in the 2012-2022 and 2002-2022 datasets, respectively. Charolais estimates showed birth weight heritability estimates of (0.36 ± 0.04, 0.42 ± 0.03), weaning weight at (0.19 ± 0.03, 0.20 ± 0.03), yearling weight at (0.07 ± 0.02, 0.13 ± 0.03) and 18-month weight at (0.10 ± 0.04, 0.17 ± 0.04) for the same periods. For Hereford (2012-2022 data only), heritability for birth weight was 0.32 ± 0.03, weaning weight 0.20 ± 0.03, yearling weight 0.32 ± 0.06, and 18-month weight 0.46 ± 0.08. Post-wean growth test traits heritability estimates were estimated on the larger data set of 2002-2022. Angus demonstrated moderate to high heritability for ADG (0.19 ± 0.05) and scrotal circumference (0.37 ± 0.07). Charolais exhibited moderate heritability for average daily gain (0.39 ± 0.30) and scrotal circumference (0.57 ± 0.28), and Hereford cattle showed moderate heritability for average daily gain (0.31 ± 0.10) but lower estimates for scrotal circumference (0.21 ± 0.10). The study emphasizes dataset limitations and recommends complete recording and genomic-based parentage testing to improve the accuracy of variance components and estimated breeding values for breeders.