The Relationship between Climatic Heat Stress Indices and feedlot performance on Nellore calves

The objective of this study was to correlate the climatic heat stress indices and the dry matter intake of Nellore young bulls during the finishing phase of a feedlot period, in the dry season in Brazil. In this trial, 222 Nellore young bulls(+350 kg initial weight and +22 month of age) were individually weighed, blocked by initial body weight and maintained in collective pens for 105 days. The same diet was provided for all animals (90 and 10%, for concentrate and forage, respectively). Data were collected during the dry season, which were measured the bioclimate index (higher ambient temperature (HT), lowest ambient temperature (LT) and average (AT) ambient temperature; temperature-humidity index (THI) and the Black Globe Humidity and Temperature Index (BGHI). Feed offered was monitored daily as well as feed refusals were collected and weighed to determine daily dry matter intake (DMI). Pearson's correlation coefficients were calculated between HT, LT, AT, THI, BGHI and DMI. Average for dry matter intake were 9.67 kg/day, although the bioclimatic averages for relative humidity were 53% and HT, LT, AT, THI and BGHI were 32.7°C, 13.2°C, 22.9°C, 69.73 respectively. There were no correlation between the dry matter intake and the bioclimatic index (r = 0.09, r = 0.13, r = 0.13, r = 0.13 and r = 0.12 for HT, LT, AT, THI and BGHI, respectively The temperature did not influence the dry matter intake of Nellore calves in feedlot system.