Teores sanguíneos de ureia e glicose como bioindicadores de eficiência alimentar em bovinos da raça nelore submetidos a diferentes dietas

Abstract

The present study aimed to evaluate the relationship between blood concentrations of urea and glucose and feed efficiency, measured through residual feed intake (RFI), in Nellore cattle subjected to feed efficiency trials under different dietary conditions. Two experiments were conducted with different forage-to-concentrate ratios: Experiment 1 (n = 29), in which animals were fed a diet containing 60% forage and 40% concentrate, and Experiment 2 (n = 24), with a diet composed of 95% forage and 5% concentrate. Blood samples were collected at mid-test and at the end of the trial, and the average of both periods was also considered. Statistical analyses included Pearson correlation and analysis of variance (ANOVA). In Experiment 1, no significant correlations were observed between RFI and urea or glucose (p > 0.05). In Experiment 2, moderate and statistically significant negative correlations were observed between RFI and urea at all evaluated time points, with r = –0.506 at mid-test, r = –0.460 at the end, and r = –0.552 for the average, indicating that lower RFI values were associated with higher blood urea concentrations. No significant association between glucose and RFI was observed in either experiment. ANOVA did not identify a significant effect of RFI classes on urea or glucose concentrations in both experiments (p > 0.05). It was concluded that blood concentrations of urea and glucose were not consistent biomarkers of feed efficiency in Nellore cattle, regardless of nutritional status, since no changes were observed even under different dietary concentrate proportions. Further studies with a larger number of animals are recommended to better understand their potential as biomarkers.