Thermal Resilience in Dairy Cattle: A Comparative Study of Heat Stress Impact on Milk Yield and Chemical Composition Across Three Breeds

Ebtissem Brahmi; Loredana  Basiricò; Umberto Bernabucci; Rachid Bouraoui

doi:10.64636/ar.44

Authors

Ebtissem Brahmi Amélioration et Développement Intégré de la Productivité Animale et des Ressources Alimentaires, LR13AGR02, Higher School of Agriculture of Mateur, University of Carthage, Mateur 7030, Tunisia; Department of Agricultural and Forest Sciences, University of Tuscia, Viterbo 01100, Italy ; Higher School of Agriculture of Kef, University of Jendouba, El Kef 7119, Tunisia https://orcid.org/0000-0001-6039-8098

Competing Interests

All authors declare no conflict of interest.
Loredana Basiricò Department of Agricultural and Forest Sciences, University of Tuscia, Viterbo 01100, Italy https://orcid.org/0000-0002-4738-3622

Competing Interests

none
Umberto Bernabucci Department of Agricultural and Forest Sciences, University of Tuscia, Viterbo 01100, Italy https://orcid.org/0000-0002-8126-3042

Competing Interests

none
Rachid Bouraoui Amélioration et Développement Intégré de la Productivité Animale et des Ressources Alimentaires, LR13AGR02, Higher School of Agriculture of Mateur, University of Carthage, Mateur 7030, Tunisia https://orcid.org/0000-0001-5667-7262

Competing Interests

none

Corresponding Author

Ebtissem Brahmi

ebtissembrahmi@gmail.com ; https://orcid.org/0000-0001-6039-8098

DOI:

https://doi.org/10.64636/ar.44

Abstract

This study examined the effects of seasonal climatic variations and parity on the milk yield and composition of Holstein (HST), Brown Swiss (BSW), and Montbéliard (MBM) dairy cows in North Tunisia from 2020 to 2024. Test day records (TD) from 199762 observations for different classes of parities (1, 2, 3 and 4+), with calculation of the Temperature-Humidity Index (THI) through Ambient Temperature (AT, ℃) and Relative Humidity (RH, %), were merged with meteorological data for analysis of the effect of seasonal heat stress and parity on the milk yield and composition. Meteorological data indicated a significant seasonal variation, with THI surpassing heat-stress thresholds during summer (mean = 75.29) and reaching its maximum in July and August. According to the results, Holstein cows had the highest peak milk yields (about 24.5 kg/d), but they were also the most sensitive to heat stress, as shown by their significant production decrease in summer. On the other hand, despite environmental challenges, BSW and MBM showed better thermotolerance and maintained consistent lactation. Analysis of milk composition revealed a strong seasonal concentration effect in all breeds, with the percentages of milk fat (MF) and milk proteins (MP) increasing in the summer and autumn months, with BSW producing the highest solid concentrations (up to 3.87% fat). Statistical analysis demonstrated significant interactions among breed, season, and parity (p < 0.05) for all traits except parity with milk fat. The results indicate that, whereas Holsteins maximize performance in temperate environments, incorporating Brown Swiss and Montbéliard genotypes provides a more resilient strategy for maintaining dairy productivity and milk quality in the increasingly hot Mediterranean climate of North Tunisia.

Keywords:

Heat stress, THI, Dairy cattle, Milk yield, Breed resilience

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Thermal Resilience in Dairy Cattle: A Comparative Study of Heat Stress Impact on Milk Yield and Chemical Composition Across Three Breeds

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