1383 Semina: Ciências Agrárias, Londrina, v. 38, n. 3, p. 1383-1392, maio/jun. 2017 Received: May 23, 2016 - Approved: Oct. 17, 2016 DOI: 10.5433/1679-0359.2017v38n3p1383 Effect of age and cyclical heat stress on the serum biochemical profle of broiler chickens Infuência da idade e do estresse cíclico de calor no perfl bioquímico sérico em frangos de corte João Paulo Rodrigues Bueno 1* ; Mara Regina Bueno de Mattos Nascimento 2 ; Julyana Machado da Silva Martins 3 ; Cristiane Ferreira Prazeres Marchini 4 ; Luciana Ruggeri Menezes Gotardo 5 ; Gabriel Miranda Ribeiro de Sousa 6 ; Antonio Vicente Mundim 2 ; Ednaldo Carvalho Guimarães 7 ; Fabrício Pereira Rinaldi ┼ Abstract This study aimed to evaluate the infuence of age and cyclical heat stress for 1 hour per day on the levels of serum proteins, metabolites, and enzymes in broiler chickens of 21-42 days of age. We used 420 male broiler chickens, Cobb Avian48 TM breed, in a completely randomized experimental design, composed of two treatments and six replicates. The treatments consisted of two thermal environments: one in which broiler chickens were raised under natural conditions of temperature and humidity for the frst 42 days of age (control) and another in which chickens were subjected to heat stress at 36°C, from days 16 to 42, for 1 hour per day (1200-1300 hours). At 21, 28, 35, and 42 days of age, approximately 5 mL of blood was collected by cardiac puncture in two birds per replicate. In each serum sample, levels of total protein, albumin, globulin, albumin:globulin ratio, aspartate aminotransferase (AST), alanine aminotransferase (ALT), and gamma-glutamyltransferase (GGT) activity and uric acid, creatinine, total cholesterol, triglycerides, high-density lipoproteins (HDL), very low density lipoproteins (VLDL), low-density lipoproteins (LDL), and glucose levels were determined. Concerning the environment and the age, no signifcant differences in the levels of glucose, uric acid, ALT, triglycerides, and very low density lipoproteins were observed. There was a signifcant interaction between the environment and the age for cholesterol and LDL values. At 21 days of age, cholesterol and LDL-cholesterol (LDL-C) were higher in birds under stress than in the control treatment birds, which did not occur in other age groups. Aspartate aminotransferase activity was higher in chickens under cyclical heat stress than in chickens subjected to control treatment and displayed a cubic response regarding the environment. The age of the birds infuenced the values of total protein, albumin, globulin, albumin:globulin (A:G) ratio, creatinine, GGT, and HDL. In conclusion, cyclical heat stress, at 36ºC, for one hour, from days 16 to 42 of age increases serum AST, whereas cholesterol and LDL-C levels increase only at day 21, indicating that birds may have adapted to heat stress. Age infuenced the activity of AST and GGT and levels of creatinine, total protein, albumin, globulin, A:G ratio, cholesterol, HDL-C, and LDL-C. Key words: Poultry. Cholesterol. Liver enzymes. Glucose. 1 Discente, Curso de Doutorado em Ciências Veterinárias, FAMEV, Universidade Federal de Uberlândia, UFU, Uberlândia, MG, Brasil. E-mail: jprbueno@hotmail.com 2 Profs. Drs., FAMEV, UFU, Uberlândia, MG, Brasil. E-mail: maran@ufu.br; antoniomundim@ufu.br 3 Discente, Curso de Doutorado em Zootecnia, EVZ, Universidade Federal de Goiás, UFG, Goiânia, GO, Brasil. E-mail: julyanamachado_zoo@hotmail.com 4 Profª Drª, Ciências Biológicas e da Saúde, Universidade de Franca, UNIFRAN, Franca, SP, Brasil. E-mail: cfprazeres@gmail.com 5 Engenheira de Alimentos, M.e em Ciências Veterinárias, FAMEV, UFU, Uberlândia, MG, Brasil. E-mail: luciana.ruggeri@ hotmail.com 6 Graduado em Medicina Veterinária, FAMEV, UFU, Uberlândia, MG, Brasil. E-mail: gabrielm.udi@hotmail.com 7 Prof. Dr., FAMAT, UFU, Uberlândia, MG, Brasil. E-mail: ecg@ufu.br ┼ In memorian. * Author for correspondence