Estimation of Genetic Parameters and Genetic Trends for Growth and Reproductive Traits in Mashona Cattle

Mashona cattle are an indigenous Sanga cattle breed from Zimbabwe, used for beef production and known for their mothering ability and adaptation to harsh tropical environments. Growth and reproductive traits are key determinants of efficiency in beef production. In this context, the main objectives of this study were to estimate (co)variance components and genetic parameters for growth and reproductive traits in registered Zimbabwean Mashona cattle and evaluate individual estimated breeding value (EBV) accuracies, genetic trends and the expected response to selection for these traits. Records of 15,020 animals born between 1960 and 2025 were analysed for birth weight (BW), weaning weight (WW), yearling weight (YW), final weight (FW), mature cow weight (MW), pre- and post-weaning average daily gain (ADG) traits, age at first calving (AFC) and inter-calving period (ICP), with records ranging from 865 for pre-weaning ADG traits to 7034 for WW. Growth trait means ranged from 27.07 ± 3.80 kg (BW) to 363.53 ± 50.13 kg (MW), while AFC and ICP averaged 1073.18 ± 152.19 and 496.11 ± 113.04 days, respectively. Direct heritability estimates for growth traits were moderate to high (0.20 ± 0.03 for YW to 0.45 ± 0.03 for WW), with maternal heritability low for BW (0.10 ± 0.03) and moderate for WW (0.20 ± 0.02). Heritability estimates for ADG ranged from low at post-weaning (0.07 ± 0.02) to moderate at pre-weaning (0.33 ± 0.11), whereas reproductive traits were lowly heritable (AFC = 0.04 ± 0.03; ICP = 0.12 ± 0.04). Strong positive genetic correlations were generally observed among most body weight traits (0.66-0.98), whereas genetic correlations involving reproductive traits were generally weak and unfavourable. Direct selection on WW is expected to increase genetic potential for YW, FW, MW and ADG_WW, but reduce ADG_YW and show weak associations with AFC and ICP. Genetic trends were positive for WW, YW and ADG_FW, while maternal genetic trends for WW declined over time (p < 0.001). No significant genetic progress was observed for other traits. Average individual EBV accuracy improved when restricted to only dams or sires with their own or progeny records. Results suggest that early selection on direct WW is expected to effectively improve growth traits but may have unintended adverse effects on reproductive and maternal traits, emphasizing the need for multi-trait selection, potentially with genomic evaluation, larger datasets and balanced selection indices.