Tree-shaded silvopastoral systems as a low-input and climate-resilient strategy to mitigate heat stress in lambs under semiarid regions.

Heat stress is a major constraint for grazing livestock in hot semiarid regions and undermines the sustainability of pasture-based production, while practical on-farm adaptation options remain limited. In this study, we evaluated a low-input silvopastoral strategy as a climate-smart alternative to full-sun irrigated pastures in Brazil's semiarid region. Integrating a moderate density of native Caatinga trees into sheep paddocks created a measurably milder microclimate than a full-sun monoculture system: silvopastoral paddocks showed slightly cooler air temperatures (reductions of up to ∼1 °C at the hottest hours) and a one-point decrease in the black-globe humidity index (BGHI 86.1 vs. 87.2; p < 0.05), indicating a lower environmental heat load. Morada Nova lambs in the silvopastoral system spent about 62% of the grazing day (∼6 h 48 min) under tree shade and ∼63% of the time grazing, with clear diurnal shifts in ingestive behavior (p < 0.001 for period effects on grazing time and bite rate). Thermal mitigation was reflected in lower heart and respiratory rates, particularly around midday (system × period interactions for HR and RR, p <0.05), even though rectal temperature remained within the normal range in both systems. A canonical discriminant analysis based on only five descriptors-air temperature, BGHI, respiratory rate, time spent grazing and time spent in the sun-correctly classified 97.9% of system × time-of-day combinations (p < 0.001), providing a concise monitoring set for field diagnosis of heat stress. Overall, our results show that introducing tree shade into irrigated pastures is a low-tech, scalable and resource-efficient intervention that reduces heat stress by 1.1 BGHI points and improves animal welfare, thereby enhancing the climate resilience of small-ruminant production systems in hot semiarid environments and contributing to cleaner, more sustainable livestock production.