PSII-24 Effect of intensification of backgrounding phase on liver, kidney and visceral fat weight in tropical beef cattle production.

Abstract The backgrounding phase is one of the least explored segments of tropical beef cattle production and has recently become a target for intensification to increase productivity and improve carcass quality in subsequent production stages. However, this intensification’s phenotypic and metabolic consequences are still unknown. Knowledge about the size of metabolically active tissues can reveal important physiological variations resulting from improved performance during backgrounding. The aim of this study was to evaluate the weight of the liver, kidneys and visceral fat according to performance during backgrounding. The study comprised 64 Nellore young bulls with an initial age of 8.7±0.4 months and an average body weight of 274.8±14.1 kg. These animals were allocated to paddocks with pastures of Urochloa brizantha cv Marandu and divided into four treatments (16 per treatment) based on differences in weight gain over 10 months of backgrounding, provided by different feed supplementation levels (mineral, protein, and/or energy-protein). The treatments were: T1 - Low (166.6±17.5 kg), T2 - Marginal (200.2±25.3 kg), T3 - Average (209.9±21.0 kg) and T4 - High (230.0±20.7 kg). At the end of the backgrounding period, with an average age of 19±0.2 months and average weight of 476.5±27.1 kg, four animals from each treatment (16 in total) were randomly selected for slaughter. The liver, kidneys and visceral fat were collected and weighed during evisceration. The data was tested for normality using the Shapiro-Wilk test and for homogeneity of variances using the Levene test. The data was analyzed by analysis of variance using linear models where the sire (parents of the young bulls) and age of the young bulls were considered in the models and the Tukey-Kramer test was used to compare means (p < 0.05). There was no difference in the weight of visceral fat (p = 0.49) or kidneys (p = 0.82). However, there was a significant difference in liver weight between treatments (p = 0.04), where animals with the greatest weight gain (T4) had heavier livers compared to those with the lowest weight gain (T1). The intensification of the backgrounding phase altered the liver weight of beef cattle, indicating that these results may reflect metabolic differences related to performance in cattle raised in a tropical system.