Impact of heat stress on cattle systems: Responses of production metrics to thermal stress

Heat stress (HS), a major consequence of climate change, significantly impairs cattle production and poses a threat to global food security. Assessing HS impacts in extensive production systems is challenging due to the diverse landscape and management practices. We evaluated the temporal HS effects on extensive beef and intensive dairy systems to identify thermal thresholds and inform adaptive strategies for sustaining productivity. The dataset comprised 1.3 million liveweight (LW) observations from 82,026 beef cattle over two years and 2,254 herd-average milk yield (MY) and compositional records from ∼300 Holstein dairy cows over seven years. The maximum temperature-humidity index (THI max ) was derived from climate data corresponding to production metrics. Cross-correlation analysis estimated lagged THI max effects, while linear regression and generalised additive models (GAM) assessed production impacts. We found an immediate (lag = 0 days) response of HS that increased LW ( b 1 = 0.0549 ± 0.0077, P < 0.0001), which progressively declined over time, reaching the highest negative influence at a 14-day lag ( b 1 = −0.0596 ± 0.0076, P < 0.0001). For MY, a delayed and substantial negative effect was observed at a 5-day lag ( b 1 = −0.0466 ± 0.0055, P < 0.0001), with similar patterns observed for protein and fat percentages at varying lags. Dairy cattle exhibited a THI threshold of 70, whereas thresholds for beef cattle remained inconclusive. Insights from dairy systems could inform HS impact assessment, the development of adaptive strategies, and the setting of regional thresholds for extensive beef production to sustain productivity and animal welfare.