Avaliação das respostas fisiológicas de bezerros Zebuínos puros e cruzados nascidos em clima subtropical

Abstract

The influence of environmental parameters on the physiological responses of purebred and crossbred Nellore calves born in a subtropical region was studied. All calves were born from high grade Nellore cows sired by Aberdeen Angus (AN), Simmental (SN), Canchim (CN) and Nellore (NI) bulls. These calves were raised under intensive management and another group of Nellore calves (NR) was raised under extensive management, similar to the typical brazilian system for beef production. Calves were observed from birth until the end of the first suckling, and the variable first suckling latency (LM) was estimated. Aapproximately 24 hours after birth, blood samples were collected from each calf to measure the plasma concentrations of total protein (PT), glucose (Gli), triiodothyronin (T 3), thyroxin (T 4), T 3:T 4 ratio, cortisol (Cort) and immunoglobulin-G (IgGb). At the same time, the calves' rectal temperature was taken and the cows and the calves were weighed. Climatic data of temperature (Temp), relative humidity (UR) and rain precipitation (PRE) in the birth day were also recorded. Physiological parameters were analyzed by least squares method using a model that included the effects of year and month of calving, group of calf, sex of calf, cow category, calving time, year x group and year x month of birth interactions and the covariables calf's weight, PRE, Temp, UR and LM. The effect of Temp was significant for the concentrations of T 3, T 4, T 4:T 3 and Cort. The concentrations of T 3 and Cort decreased and the levels of T 4 and T 4:T 3 ratio increased as Temp increased. Similarly, the concentration of Cort increased and the concentrations of IgGb and PT decreased as LM increased. PT level was significantly higher in NR calves than in NI ones. © 2006 Sociedade Brasileira de Zootecnia.