Heat stress affects dairy and beef cattle welfare globally, reducing production, reproductive performance, and welfare during periods of high temperature and humidity. Proactive management significantly reduces heat stress impacts.
Cattle are homoeothermic—maintaining body temperature within narrow limits regardless of ambient temperature. When heat load from radiation, convection, and metabolic activity exceeds heat dissipation capacity, core temperature rises, causing heat stress. Dairy cows are particularly vulnerable due to high metabolic heat from ruminant fermentation and milk production. The Temperature-Humidity Index (THI) above 68 indicates heat stress; above 72, severe welfare impacts occur.
Signs of heat stress include: increased respiratory rate (above 60 breaths per minute indicates stress; above 80 indicates severe stress); reduced dry matter intake; reduced milk yield; increased water intake; altered behaviour (bunching, seeking shade, reduced activity); and in severe cases, recumbency, salivation, and death. Reproductive performance declines with embryonic heat sensitivity reducing conception rates. Immune function is compromised, increasing disease susceptibility.
Shade provision for housed and pasture cattle reduces radiant heat load. Sprinkler systems (intermittent large-droplet sprinklers rather than misters) cool cattle through evaporation; fans increase air movement facilitating evaporative cooling. Ventilation management in covered housing maintains air movement preventing heat accumulation. Adjusting feeding times to cooler periods (early morning, late evening) maintains dry matter intake during hot weather.
Heat-stressed cows reduce feed intake, creating negative energy balance with welfare and production consequences. Increasing dietary energy density through rumen-protected fat maintains energy supply despite reduced intake. Electrolyte supplementation replaces sodium and potassium lost through sweating. Buffering the diet with sodium bicarbonate supports rumen function despite reduced saliva production from diminished rumination. Ensuring continuous water availability—consumption can double during heat stress—is critical.