Thermal comfort and performance Holstein/Gir calves housed in individual shelters with different covers/Conforto termico e desempenho de bezerras Girolando alojadas em abrigos individuais com diferentes coberturas

This research was developed with the aim to characterize the effects of thermal ambience on physiological responses, comfort indexes and Holstein/Gir calves performance, housed in individual hutches covered with different materials. The experimental period was from January to March of 2012, lasting for 56 days, conducted by 24 crossbred calves with genetic of 7/8 Holstein-Gir. The treatments consisted of three types of covering materials, palm straw, recycled polymer tile and fiber cement tile. A completely randomized design was adopted and in order to compare means the Tukey test (p < 0.05) was used. The enthalpy and the radiant thermal load differed statistically in all treatments, being the lowest values presented by the recycled- tile-covered housings, 59.3 kJ [kg.sup.-1] dry air and 444.8 W [m.sup.-2], respectively. As for the physiological variables, there was no significant difference in any of the studied variables, however, the respiratory frequency in all treatments was high, and more emphasized on animals under fiber cement covered hutches (57.2 mov min- 1) indicating that the animals were under heat stress. Key words: animal ambience dairy cattle weight gain roofing materials Esta pesquisa foi desenvolvida com o objetivo de caracterizar os efeitos do ambiente termico nos indices de conforto, respostas fisiologicas e no desempenho de bezerras Girolando, alojadas em abrigos individuais cobertos com diferentes materiais. O experimento foi realizado entre janeiro e marco de 2012, com duracao de 56 dias, conduzido com 24 bezerras de composicao genetica 7/8 Holandes-Gir aos 15 dias de vida e com peso medio de 40,6 kg. Os tratamentos consistiram em tres tipos de cobertura, palha de palmeira, telha de polimero reciclado e telha de fibrocimento, com 8 repeticoes. O delineamento experimental adotado foi o inteiramente casualizado com comparacao entre medias pelo teste de Tukey (p < 0,05). A entalpia e a carga termica radiante diferiram estatisticamente em todos os tratamentos sendo os menores valores apresentados pelos abrigos com cobertura de telha reciclada, 59,3 kJ [kg.sup.-1] de ar seco e 444,8 W [m.sup.-2], respectivamente. Nao houve diferenca significativa em nenhuma das variaveis fisiologicas estudadas, porem a frequencia respiratoria esteve elevada em todos os tratamentos sendo mais acentuada nos animais sob cobertura de fibrocimento (57,2 mov min-1) indicando mais suscetibilidade ao estresse termico. Palavras-chave: ambiencia animal bovinos de l