Levels of IGF-1, thyroxine, triiodothyronine and cortisol in yearling bulls in feedlot or silvopastoral system
M. E. Romero Santamaría1 J. A. Ramírez Godínez1*; G. Corral Flores1; A. Flores Mariñelarena1; C. Rodríguez Muela1; P. F. Mancillas Flores1; J. A. Ortega Gutiérrez1 and A. Ayala Burgos2
1Facultad de Zootecnia y Ecología, Universidad Autónoma de Chihuahua, Chihuahua, México. 2Campus de Ciencias Biológicas y Agropecuarias, Universidad Autónoma de Yucatán, Yucatán, México.
*corresponding author´s e-mail: firstname.lastname@example.org
The aim of this research was to compare serum levels of Insulin-like growth factor (IGF-1), triiodothyronine (T3), thyroxine (T4) and Cortisol (C) in 80 yearling bulls from two genetic groups; BrahmanXCharolais (40 BhXCH), BrahmanXBrown Swiss (40 BhXBS); which were randomly assigned to the feeding system in the dry tropic region in Michoacan, Mexico; feedlot (F) or intensive silvopastoral (ISPS). Animals were bled from the jugular vein at 0, 71, 132, and 195 days to quantify serum hormones by radioimmunoassay. Effects of feeding system and genetic group across time were analyzed using mixed models from SAS with time repeated measures. Differences were found for IGF-1, T3 and C by feeding system (P<0.05). Means were higher in IGF-1 (201.36±8.25; 117.74±7.74 ng mL-1).T3 of F was higher (P<0.05) than ISPS (1.15±0.03;0.99±0.03 ng mL-1). C of F was lower (P<0.05) than ISPS (19.13±1.80 ; 25.30±1.71 ng mL-1), respectively. Genetic group had no effect (P>0.05) on T3, T4 and Cconcentration; however, effect on IGF-1 was found (P<0.05). T4 was similar (P>0.05) between systems. It was conclude that IGF-1 and T3 were higher in F than in ISPS. Genetic group only had effect on IGF-1. Handling of ISPS animals were more susceptible to stress than F, since the values for C were higher but decreased with time.
Key words: silvopastoral, IGF-1, thyroid hormones, bovine.