Disease & heat resistance
Authors: Amanda Maiorano (Federal University of Uberlandia) , Mariana Medeiros (Federal University of Uberlandia) , Larissa Mamede (Federal University of Uberlandia) , Gustavo Messias (Federal University of Uberlandia) , Davi Salandini (Federal University of Uberlandia) , Nariely Souza (BRF) , Ana Carolina Tieppo (Federal University of Uberlandia) , Miller Teodoro (São Paulo State University) , Ariadne Silva (Federal University of Uberlandia) , Mara Regina Nascimento (Federal University of Uberlandia)
The objective of this study was to evaluate the effects of genetic composition (GC) and thermal environment on thermophysiological traits of Girolando heifers. The experiment was conducted on a commercial dairy farm located in Goiás, Brazil. Eighteen Girolando heifers were studied: seven ½H, five ¾H and six 5/8H (Holstein breed proportions). The thermophysiological traits measured included respiratory rate (RR), rectal temperature (RT), and frontal temperature (FT) during the coldest (July) and warmest (October) months. Air temperature and relative humidity data were obtained from the NASA/POWER platform, and the Temperature-Humidity Index (THI) was calculated using the equation of Berman et al. (2016). Repeated-measures mixed models were fitted to evaluate the effects of GC, shift of the day, body weight (BW), age, season and diurnal thermal amplitude. Pearson correlations between THI and thermophysiological variables were estimated. Regardless of the month, mean RR values were above the normal range reported for cattle. Minimum RR values remained within the reference range, whereas maximum values exceeded the upper limit. The RT remained stable across months, close to the physiological thresholds. The FT exhibited the greatest variation, being lower in July and higher in October. A positive correlation was observed between THI and physiological traits, with FT being the most responsive to environmental variation. BW had a significant negative effect on RR (p≦0.01), RT (p≦0.001), and FT (p≦0.1). The GC significantly influenced FT, with higher values observed in 1/2H and 5/8H heifers compared with 3/4H (p≦0.001), although no differences were detected between 1/2H and 5/8H. The season had a marginal effect (p< 0.10), with a trend toward higher FT values in October. The shift of the day effect was significant for FT (p≤0.0003), with higher values recorded in the afternoon than in the morning. A significant interaction between GC and season was found for RR and RT. In July, 1/2H heifers showed higher RR, while in October, 3/4H heifers had the lowest mean RR. The ranking pattern among GC groups also varied across seasons for RT, where 3/4H heifers presented lower RT than 1/2H and 5/8H in July and higher RT values in October (p≤0.013). No significant differences among GC were observed in October. The results indicate that FT is the most sensitive bioindicator of heat stress; however, the combined use of all thermophysiological traits provides a more comprehensive assessment of animal thermal response. The 1/2H and 5/8H heifers activated heat dissipation mechanisms more rapidly than 3/4H heifers, suggesting their potential advantage under tropical heat stress conditions.
Keywords: 2026
How to Cite: Maiorano, A. , Medeiros, M. , Mamede, L. , Messias, G. , Salandini, D. , Souza, N. , Tieppo, A. , Teodoro, M. , Silva, A. & Nascimento, M. (2026) “Influence of genetic composition and thermal environment on thermophysiological traits of Girolando heifers”, World Congress on Genetics Applied to Livestock Production Digital Archive. 2026(1). doi: https://doi.org/10.31274/wcgalp.23456