Thermal environment and daily patterns shaping the water intake of Caracu Young bulls in a tropical region

The aim of this study was to evaluate the effects of the thermal environment, body weight, and hours on the water intake of Caracu young bulls raised in a tropical region. Forty-six animals (mean±SD: 247±230 days old; 226±35 kg body weight) participated in a Feed Efficiency Test over 68 days (June–September 2024) in Sertãozinho, Brazil. Hourly individual water intake (L) and daily body weight (BW, kg) were recorded using electronic water troughs (Intergado^®). Hourly environmental data were obtained from NASA-POWER, and the 3-hour moving average of the Black Globe Humidity Index (BGHI) was calculated. Data were analyzed using a Generalized Additive Mixed Model (GAMM), including smooth terms for BGHI and BW, hour (24 h) as a fixed effect, and a random intercept for animal, using REML. BGHI had a non-linear effect (p<0.05), with two inflection points (71 and 76.7). Up to BGHI 71, water intake increased (+0.105 L/ BGHI unit); between 71.1 and 76.7, there was a reduction (–0.041 L/ BGHI unit); and above 76.7, intake increased again (+0.0128 L/ BGHI unit). The model also showed a diurnal pattern in water intake, with low consumption during the night and early morning (hours 0–4; p>0.05). Intake rose around 5 h (+0.43 L; p = 0.018) and reached its highest levels between 8 h and 11 h (+1.6 to +2.1 L; p<0.001). In the afternoon, consumption gradually declined and returned to baseline by late afternoon (12 h–17 h; p<0.01). A secondary increase occurred at 22 h (+0.27 L; p=0.045). BW influenced (p<0.001) water intake; for each additional kilogram, it increased by 0.018 L. Overall, these findings show that thermal environment drives water intake. Although individual increases may seem small, when multiplied across many animals over several days under heat stress, they can reduce water-use efficiency in the system. This reinforces the need for management practices that reduce heat load and ensure adequate water availability in tropical production systems.