Assessing climatic effects on milk yield traits using sinusoidal modelling in dairy cows.

Area of Science:

• Animal Science
• Environmental Science
• Dairy Production

Background:

• Climatic variations significantly affect dairy cow productivity and well-being.
• Understanding these effects is crucial for sustainable dairy farming practices.

Purpose of the Study:

• To adapt sinusoidal functions (SIN-F) for describing circannual variations in climate and dairy cow production traits.
• To compare SIN-F application across different farm types (plains vs. hills/mountains) and dairy breeds.
• To evaluate mid-term deviations from SIN-F as indicators of heat stress.

Main Methods:

• Utilized data from 39 weather stations and 65,883 test-day records from 117 herds.
• Applied sinusoidal functions (SIN-F) to model circannual variations in daily milk yield (dMY), fat (FAT%), and protein (PROT%).
• Analyzed herd, stage of lactation, parity, year, altitude, and breed effects on milk traits.

Main Results:

• Herd and lactation stage were major sources of variation in milk traits. SIN-F explained 2.4-12.8% of long-term variation, while mid-term deviations accounted for 0.4-2%.
• Milk fat and protein peaked in winter and nadired in summer, with dMY peaking later. Plains herds showed greater dMY variation than hills/mountains herds.
• Simmental and Brown Swiss breeds exhibited smaller milk yield amplitude and delayed SIN-F compared to Holsteins, suggesting greater climate resilience.

Conclusions:

• Circannual SIN-F and its variations are effective tools for assessing climatological impacts on dairy production.
• Mid-term deviations from SIN-F, particularly during summer, can serve as indicators of heat stress in dairy cows.
• The study highlights breed and farm type differences in response to climatic variations, informing management strategies.