PSVI-22 Cortisol and acute-phase proteins of lambs submitted to silvopastoral systems.

摘要

The objective of this study was to evaluate the effect of heat stress on animal welfare by determining blood cortisol and acute-phase proteins of sheep under silvopastoral systems or under full sun, during rainy season in Jaboticabal, Brazil. Twenty-four male crossbred Santa Inês × Dorper lambs (23 ± 3.3 kg BW) were distributed in a complete randomized design, and assigned to one of the three experimental treatments (Unshaded, Moderate Shading and Intense Shading), in a rotational grazing system. Six paddocks of each treatment containing Eucalyptus trees and Massai grass were used. Animals stayed for 10h grazing, and, at night, were held to a barn with access to mineral salt and water. Blood samples were taken at midday, one day before animals start the grazing cycle, and at d7 and d14 after the beginning of the grazing cycle, in the paddocks. Animals were adapted to the handling to avoid unwanted cortisol response. Protein fractionation was performed by the polyacrylamide gel electrophoresis technique containing sodium dodecyl sulfate. Cortisol was performed by validating the methodology using a parallelism curve, and the values were read in a specific spectrophotometer. Data were analyzed using PROC MIXED of SAS. No differences in cortisol concentrations were observed among treatments. However, values observed for all treatments were above the reference limits, ranging from 1.4 and 3.1 μg/dL, regardless the day. Differences were observed along the period of evaluation for total protein (TP) and haptoglobin (Hapt; < 0.0001), which increased after 14d animals started grazing (TP: d0 = 6.66 g/dL; d7 = 6.86 g/dL; d14 = 7.12 g/dL; Hapt: d0 = 0.004, d7 = 0.0059; d14 = 0.0074 g/dL), regardless the treatment. Therefore, the severity of heat stress depends, to a large extent, on the fluctuations of the ambient temperature during and along the d.