Disease & heat resistance

Influence of genetic composition and thermal environment on thermophysiological traits of Girolando heifers

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Abstract

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

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): 2281476. doi: https://doi.org/10.31274/wcgalp.23456

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