Blood parameter of Nellore steers submitted to different levels of feed intake

Resumen

Blood parameters of 18 Nellore steers submitted to high concentrate diet in two sequential feeding regimes (Phase 1: restriction and Phase 2: ad libitum feed) were evaluated. In the first phase, steers were fed during 56 days in three intake levels of dry matter (ad libitum, 75 g dry matter (DM)/kg metabolic body weight (BW^0.75) or 60 g DM/kg BW^0.75. In the second phase, from the 57^th day of confinement, animals fed 60 g DM/kg BW^0.75 and 75 g DM/kg BW^0.75 received feed ad libitum until the 136^th day. In the 8^th, 27^th, 55^th (first phase), 71^st, 84^th, 112^th and 132^nd (second phase day of experimental period, blood samples were collected and insulin-like growth factor I (IGF-I), triiodothyronine (T3), thyroxine (T4), glucose, plasma ureic nitrogen (PUN) and total protein (TP) were determined. In the first phase IGF-I, T4, glucose and total protein concentration was not different among treatments (P>0.05) and there was no interaction between treatment and time (P>0.05). There was an interaction among treatments and time on T3 and plasma ureic nitrogen (P<0.01). In the second phase IGF-I, T3, T4, glucose and total protein concentration was not different among treatments and there was no interaction between treatment and time (P>0.05). For plasma ureic nitrogen concentration there was an interaction among treatments and time (P=0.02). Lower levels of diet intake can be used to improve animal performance in feedlot.