Thermal tolerance, performance, and physiology of egg-type pullets when subjected to different levels of heat stress during the brooding and growing phases sequentially

• Ano de defesa: 2019
• Autor(a) principal: Cândido, Márcia Gabrielle Lima
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Universidade Federal de Viçosa
• Palavras-chave em Português: Aclimatação; Meio Ambiente; Aves - Stress (Fisiologia); Calor - efeito fisiologico; Temperatura Corporal - regulação; Aves - Criação; Construções Rurais e Ambiência
• Link de acesso: https://locus.ufv.br//handle/123456789/27346

Brazil is a prominent producer of animal protein, especially regarding the poultry sector, being the largest egg producer in South America. As a tropical and subtropical country, Brazil is characterized by its low annual thermal amplitude and high temperatures during the year, across most of its territory. Thus, the thermal comfort of hens, especially regarding heat stress, has great influence on poultry performance. Heat stress can lead to a reduction in bird productivity, affecting their productive and physiological performance and behavior; in extreme cases it may cause death. Therefore, it is very important to know and to keep updated the zone of thermal comfort of birds, since this zone varies according to, for example, the age of the bird, productive phase, breeding environment, sex, genetics and previous exposure to hot or cold. In view of the above, this research was conducted with the aim to determine the thermal comfort zone for laying pullets during the growing phase based on physiological parameters and performance. Also evaluated was the effects of acclimatization of chicks during the brooding phase (first 6 weeks of life) when exposed to different thermal environments during the growing phase (7th to 17th week of life). This work was carried out in climatic chambers located in AMBIAGRO - DEA / UFV, with Lohmann LSL Lite laying pullets. It was conducted in two phases: Phase I with 648 birds from 1 day to 6 weeks of age and Phase II with 418 birds from 7 to 17 weeks of age. During Phase I the birds were subjected to one of three thermal environments, characterized as cold stress, comfort, and heat stress. Phase I aimed to prepare the birds for Phase II. At the beginning of the 7th week of age, birds from Phase I were randomly redistributed in four climatic chambers with different temperatures (thermal comfort, 20/20 °C and three levels of heat stress: mild, 25/20 °C, moderate, 30/20 °C, severe, 35/20 °C), each climatic chamber of Phase II received 5 groups of birds coming from each thermal environment of Phase I. During Phase II, during the night period all birds were kept in a thermal comfort environment (20/20 °C). Performance parameters (feed intake, feed conversion, body weight) and physiological parameters (cloacal and body surface temperature, T3 and T4 hormone concentrations of blood plasma) were analyzed. No influence of Phase I on the performance of birds during Phase II was observed. In general, birds maintained at temperatures of 20/20 °C and 25/20 °C presented better performance than those exposed to 30/20 °C and 35/20 °C, indicating that this would be the desired environmental temperature range for the growing environment of pullets, from 7 to 17 weeks of age.