ZINC-MEDIATED MODULATION OF HEAT STRESS RESPONSES IN DAIRY ANIMALS

Abstract

Heat stress is a major environmental constraint affecting the productivity, health, and welfare of dairy animals, particularly in tropical and subtropical regions. Elevated ambient temperature and humidity impair thermoregulation, reduce dry matter intake, suppress immune function, and alter metabolic processes, leading to substantial economic losses in dairy production systems. Nutritional interventions have emerged as practical approaches to mitigate the detrimental effects of heat stress, among which zinc supplementation has gained considerable attention due to its diverse physiological functions. Zinc is an essential trace mineral involved in antioxidant defense, immune regulation, enzyme activity, and endocrine metabolism. Zinc sulfate, a commonly used inorganic source of zinc, is widely incorporated into dairy rations because of its availability and cost-effectiveness. Studies have demonstrated that dietary supplementation with zinc sulfate at levels ranging from 60 to 120 mg Zn/kg dry matter improves heat stress tolerance in dairy animals. For instance, zinc-supplemented cows exhibited a 12–18% increase in Cu–Zn superoxide dismutase activity, a 15–25% reduction in malondialdehyde concentration, and a 10–20% decrease in plasma cortisol levels compared with non-supplemented heat-stressed controls. Improvements in immune status have also been reported, including 8–15% higher lymphocyte proliferation, reduced pro-inflammatory cytokine expression, and enhanced udder health. In lactating dairy cows, zinc supplementation was associated with 3–7% higher dry matter intake and maintenance of milk yield during periods of severe thermal stress, with increases in milk production ranging from 0.5 to 1.5 kg/day in some studies. Furthermore, rectal temperature and respiration rate were reduced by approximately 0.3–0.6°C and 8–15 breaths/min, respectively, indicating improved thermoregulatory capacity. Collectively, the available evidence suggests that zinc sulfate supplementation enhances antioxidant defenses, modulates endocrine and immune responses, and improves physiological resilience under heat stress conditions. Therefore, zinc sulfate supplementation represents an effective and economical nutritional strategy for improving heat stress adaptation and sustaining productivity in dairy animals.