Índices microclimáticos e indicativos de estresse térmico em bovinos de corte
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2018-08-13
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Universidade Federal de Goiás
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The objective was to use microclimatic indexes and to propose indicators of thermal stress in beef cattle to evaluate animal production systems. For that, two experiments were carried out: (i) using infrared thermography to evaluate microclimate and thermal comfort in silvopastoral systems; and (ii) evaluating the physiological adaptability of beef cattle in feedlot and pasture submitted to thermal stress. The first experiment was conducted at the Empresa Brasileira de Pesquisa Agropecuária, in Campo Grande, Mato Grosso do Sul, from June 2015 to February 2016. The evaluations were carried out in two silvopastoral systems with different densities and spatial arrangements of cultivated and native trees, from 08h to 16h, with intervals of one hour between evaluations. Infrared radiation emissions of temperature (°C) and humidity (%) of the canopy and pasture surface were recorded, in the shadow projection and in the full sun. At the same time, the microclimatic parameters were evaluated and the main thermal comfort indeces were subsequently calculated. Variations of canopy and pasture temperature and humidity were observed, with direct influences on microclimate and animal thermal comfort. The greatest fluctuations occurred during the summer and at noon with substantial improvements in the environment under the canopy. The Principal Components Analysis extracted two components in order of their importance to explain 70.6% of the total variance observed between the variables. Moderate and strong correlations (r ≥ 0.63; or, r ≤ 0.80) showed positive linear effects (R²adj ≥ 0.40, or, ≤ 0.63) between thermography, microclimate and thermal comfort indeces. The results show that temperatures and humidities of canopy and pasture surfaces can be continuously monitored using infrared thermal imagers, making it a potential tool (r ≥ 0.53; or, r ≤ 0.78) for microclimate prediction and thermal comfort in silvopastoral systems. The second experiment was conducted on farms located in Civitella Paganico, Grosseto province, Italy, in partnership with Università di Pisa (Italy), from May to September 2017, using 60 animals (20 Aubrac, 20 Maremmano and 20 ½ Maremmano x ½ Piemontês) divided into two production systems (confinement and pasture). Cortisol in the hair, physiological variables (rectal, hair and skin temperatures, cardiac and respiratory frequency) and hematological variables (complete blood count) were evaluated. No effects of production system were observed (P> 0.05). However, the effects of genetic groups, the evaluation period and the interaction between genetic groups and production systems significantly affected (P <0.05) all evaluated parameters. The crossbreed genetic group had the highest concentrations of cortisol during the whole experimental period, favoring the greater variations in the physiological parameters and being more susceptible to chronic stress. Non-invasive methods, such as the sampling of hairs on animals and the application of infrared thermography for the evaluation of production systems, contribute to the advancement of scientific research in several areas of knowledge.
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KARVATTE JUNIOR, N. Índices microclimáticos e indicativos de estresse térmico em bovinos de corte. 2018. 85 f. Tese (Doutorado em Zootecnia) - Universidade Federal de Goiás, Goiânia, 2018.