PS12-19. Metabolic Indicators and Body Development of Beef and Dairy-origin Male Cattle During Feedlot Growing and Finishing.

Abstract The increasing use of dairy-origin males for beef production has raised interest in understanding their metabolic responses and growth patterns compared with specialized beef genotypes. The objective of this study was to evaluate metabolic indicators and body development patterns of beef and dairy-origin male cattle. Animals (n = 64) from four genetic groups representing Brazilian beef production systems as follows: Angus × Nellore castrated (ANG), dairy crossbred non-castrated (DC), Holstein castrated (HOL), and Nellore non-castrated (NEL), with an initial body weight (iBW) of 194 ± 2.4 kg were used. The experiment was conducted as a randomized complete block design, with animals blocked by iBW. Pens containing two animals were considered the experimental unit. Animals were fed sequential diets during the experimental period, representing a transition from forage-based growing diets to a high-concentrate finishing diet. Biometric measurements, including thoracic circumference (CIR), body length (BL), and estimated body volume (BV), were recorded on days 1, 85, 197, and 297 of the experimental period. Blood samples were collected on days 114 and 238 to determine glucose, aspartate aminotransferase (AST), creatinine, and alkaline phosphatase (AP) concentrations. Data were analyzed using a mixed model with repeated measures over time, including treatment, time, and their interaction as fixed effects, with block as a random effect and pen as the experimental unit. Biometric traits were affected by time (P < 0.01), reflecting progressive structural growth during the feeding period. CIR increased from 134.0 cm at the beginning of the experiment to 187.4 cm at the end of finishing. BL and BV presented significant treatment × time interactions (P < 0.05), indicating different growth trajectories among genetic groups. Differences among treatments became more evident during the finishing phase, when HOL animals showed greater BL and BV, DC animals presented lower values, and ANG and NEL showed intermediate patterns. BV increased from approximately 0.17 m³ to about 0.42 m³ throughout the experiment. Blood metabolites also varied among genetic groups. Glucose concentration differed among treatments (P = 0.02) and increased over time (P < 0.01), with greater values observed for DC and NEL animals. Creatinine concentration was affected by treatment (P < 0.05), with higher concentrations in ANG and DC compared with HOL. AP differed among treatments (P = 0.05), with greater values observed in NEL animals and lower values in ANG. Genetic group influenced metabolic profile and body development during feeding period. HOL animals showed greater structural growth in the final evaluations, whereas ANG and DC presented higher creatinine concentrations, suggesting greater relative muscle mass. Blood metabolites reflected the metabolic status during periods of active growth occurring between biometric evaluations, indicating that dairy-origin cattle exhibit intermediate metabolic and growth patterns compared with specialized beef genotypes.