Abstract
ABSTRACT This study aimed to assess the environmental variables, thermal comfort indices and physiological responses of calves in outdoor holding pens shaded with geosynthetics. Twenty crossbred females (Giroland, Jersey and Holstein) in the suckling phase (from birth to 90 days old) with an average initial live weight of 40.6 kg were used. A completely randomized block design was used, in a 4 × 3 factorial scheme with five replicates. The roofing materials (polyethylene mesh, geocomposite drainage layer, nonwoven geotextile and woven geotextile) were the first factor and time periods (8 to 10 a.m., 12 to 2 p.m. and 4 to 6 p.m.) the second factor. The following environmental variables were measured to calculate thermal comfort indices: temperature-humidity index, black globe-humidity index and enthalpy. The physiological variables analyzed were respiratory rate, rectal temperature and skin temperature. Environmental variables and thermal comfort indices did not differ between the different roof types, however, a significant difference (p ≤ 0.01) was observed between the time periods, with 12 to 2 p.m. being the most critical period. The lowest average respiratory rate (60.3 breaths min-1) and rectal temperature (38.9 °C) were recorded for the animals kept under the geocomposite drainage layer roof. There was a significant difference (p ≤ 0.05) for interaction between treatment and time periods for the cannon area. The geosynthetics studied can be used as roofing material for outdoor holding pens, with the geocomposite drainage layer being the most indicated for tropical regions.
Highlights
Heat stress is one of the limiting factors for animal production (Rashamol et al, 2019)
There was no significant interaction between roofing materials and time periods for the environmental variables or thermal comfort indices (p ≤ 0.01)
No significant differences were found between roofing materials for the environmental variables or thermal comfort indices (p > 0.05); there were significant differences between time periods
Summary
Heat stress is one of the limiting factors for animal production (Rashamol et al, 2019). Animals exposed to this condition exhibit altered physiological variables (Cattelam & Vale, 2013). Increased respiratory rate is the first visible sign of heat stress (Barnabé et al, 2015), resulting in the intensification of latent heat loss processes in an attempt to maintain homeothermy (Wang et al, 2020). When this mechanism is insufficient, the rectal temperature of animals may increase (Rossarolla, 2007). Thermal imaging is used to diagnose heat stress in animals (Barreto et al, 2020), since it measures the thermal radiation emitted from the surface of the body (Roberto et al, 2014)
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