Henrique G. Reolon ¹ Natalya G. Abduch ^1,2 Ana Claudia Freitas ^1,3 Rafael M. Silva ⁴ Breno D. Fragomeni ⁵ Daniela Lourenco ⁶ Fernando Baldi ⁷ Claudia Cristina Paro Paz ^2,8 Nedenia B. Stafuzza ^1*

• ¹ Instituto de Zootecnia, Sertãozinho, Brazil
• ² Universidade de São Paulo (USP), Ribeirão Preto, São Paulo, Brazil
• ³ Empresa de Pesquisa Agropecuária de Minas Gerais (EPAMIG), Patos de Minas, Brazil
• ⁴ Angus Genetics Inc, Saint Joseph, United States
• ⁵ University of Connecticut, Storrs, Connecticut, United States
• ⁶ University of Georgia, Athens, Georgia, United States
• ⁷ Universidade Estadual Paulista (UNESP), Jaboticabal, Brazil
• ⁸ Instituto de Zootecnia, São José do Rio Preto, Brazil

Background: Identifying molecular mechanisms responsible for the response to heat stress is essential to increase production, reproduction, health, and welfare. This study aimed to identify early biological responses and potential biomarkers involved in the response to heat stress and animal's recovery in tropically adapted beef cattle through proteomic analysis of blood plasma.Methods: Blood samples were collected from 14 Caracu males during the heat stress peak (HSP) and 16 hours after it (heat stress recovery -HSR) assessed based on wet bulb globe temperature index and rectal temperature. Proteome was investigated by liquid chromatography-tandem mass spectrometry from plasma samples, and the differentially regulated proteins were evaluated by functional enrichment analysis using DAVID tool. The protein-protein interaction network was evaluated by STRING tool. Results: A total of 1,550 proteins were detected in both time points, of which 84 and 65 were downregulated and up-regulated during HSR, respectively. Among the differentially regulated proteins with the highest absolute log-fold change values, those encoded by the GABBR1, EPHA2, DUSP5, MUC2, DGCR8, MAP2K7, ADRA1A, CXADR, TOPBP1, and NEB genes were highlighted as potential biomarkers because of their roles in response to heat stress. The functional enrichment analysis revealed that 65 Gene Ontology terms and 34 pathways were significant (p < 0.05). We highlighted those that could be associated with the response to heat stress, such as those related to the immune system, complement system, hemostasis, calcium, ECM-receptor interaction, and PI3K-Akt and MAPK signaling pathways. In addition, the protein-protein interaction network analysis revealed several complement and coagulation proteins and acute-phase proteins as important nodes based on their centrality and edges.Identifying differentially regulated proteins and their relationship, as well as their roles in key pathways contribute to improve the knowledge of the mechanisms behind the response to heat stress in naturally adapted cattle breeds. In addition, proteins highlighted herein are potential biomarkers involved in the early response and recovery from heat stress in tropically adapted beef cattle.