Evaluation of LiGAPS-Beef to assess extensive pasture-based beef production in three agro-ecological regions in South Africa

Summary

Quantifying the performance of beef cattle in diverse agro-ecological regions with different climatic conditions could be used by stakeholders to develop region-specific resilience strategies and optimize livestock production systems. This study evaluated the ability of the mechanistic LiGAPS-Beef model as a tool to quantify beef production of selected cattle breed types in diverse agro-ecological regions in South Africa. The average daily gain (ADG) was simulated for Bos taurus, composite and Sanga breed types in three different agro-ecological regions i.e. Bloemfontein (semi-arid), Phalaborwa (semi-desert) and Buffalo Berlin (temperate oceanic). Simulated ADGs were compared to measured ADGs from eight experiments for calibration and validation. After calibration, the model simulated ADG of breed types with a mean absolute percentage error (MAPE) of 23%. Simulated and measured values were positively correlated (r = 0.88) and largely in agreement (index of agreement=0.92). Factors that define and limit growth, such as the genotype, heat stress, cold stress, and digestion capacity limitation, were identified. Consistent with literature, the model showed more heat stress on Bos taurus breed types than on composite and Sanga breed types in Phalaborwa, which was the warmest region included in the study. Sensitivity analysis by changing input parameters by ± 10% showed that the model was more sensitive to changes in metabolizable energy (ME) than crude protein (CP) implying that the accuracy of ME must be prioritised. Overall, the results showed that model performance was adequate and thus the LiGAPS-Beef model can be used to explore the effects of climate change and adaptive breeding strategies in future studies in South Africa.