Modeling heat stress under different environmental conditions

Area of Science:

• Animal Science
• Climate Change Impact
• Dairy Production

Background:

• Climate change is increasing global temperatures and extreme weather events, raising concerns about heat stress (HS) in livestock.
• Understanding the impact of temperature and humidity on dairy cattle productivity is crucial for adapting management strategies.
• Existing models for HS effects may not fully capture regional and population-specific variations in dairy cows.

Purpose of the Study:

• To evaluate the effects of temperature and humidity on milk production (yield, fat, protein) in Holstein dairy cattle across diverse European regions.
• To identify differences and similarities in heat stress thresholds and responses among populations in Belgium, Luxembourg, Slovenia, and Spain.
• To compare different modeling approaches for optimizing heat stress effect modeling in dairy cattle.

Main Methods:

• Merged milk test day data (1999-2010) with meteorological data (temperature, humidity) for Holstein populations in four European regions.
• Calculated daily average and maximum Temperature-Humidity Index (THIavg, THImax) to quantify heat load.
• Utilized change point techniques and compared broken line, quadratic, and cubic models to determine HS thresholds and response patterns.

Main Results:

• Heat stress thresholds varied across traits and regions, with milk yield showing an inverted U-shaped response peaking around 73 THImax.
• Fat and protein production had lower HS thresholds than milk yield, with Spain showing higher thresholds compared to other countries.
• A cubic polynomial model best described the production response to heat load, indicating higher-producing cows had less persistent production under heat stress.

Conclusions:

• Dairy cattle exhibit distinct heat stress responses influenced by climate, production systems, and individual productivity levels.
• Animals in temperate climates (Belgium, Luxembourg) experienced heat stress at lower heat loads compared to those in warmer climates (Spain).
• The findings highlight the need for region-specific and cow-specific models to accurately predict and manage heat stress impacts on dairy production.