Residual feed intake and reproductive-related parameters in yearling Brangus bulls

Abstract Residual feed intake (RFI) is a widely employed metric to estimate feed efficiency, which compares actual feed intake to expected feed intake. Enhancing feed efficiency while maintaining reproductive performance is critical to maximizing the profitability of beef production systems. Published data exhibit conflicting results concerning the impact of RFI on reproductive parameters. Our objective was to evaluate the relationship between RFI and reproductive parameters in young Brangus bulls. Sixty bulls were randomly selected at the beginning of a 56-d feed efficiency test. At the start, scrotal circumference (SC) was measured, blood samples were taken for testosterone concentration analysis, and semen samples were collected by electroejaculation. Fresh semen was visually evaluated for motility, morphology, and plasma membrane integrity. Sperm kinematics and concentration were objectively determined via computer-assisted sperm analysis (CASA-IVOS II System). At the end of the test, bulls were classified as feed efficient (low RFI: LRFI) or feed inefficient (high RFI: HRFI) and grouped based on RFI divergence. Two models were constructed to analyze data: one using all bulls (Halves, n = 58) and one using the 25% extremes of the population (Tails, n = 30). Data were compared using a completely randomized design. Using the halves model, only major defects (P < 0.04) and total defects (P = 0.014) were significantly affected by RFI group, with LRFI bulls showing a lower proportion of abnormal sperm cells. In the tails model, only SC (P = 0.01) was significantly affected by RFI, with LRFI bulls having a larger SC compared to HRFI bulls. The RFI group did not affect CASA-derived traits in either model. In conclusion, most fertility-related measurements were not affected by RFI status in young Brangus bulls. These results suggest that selection for feed efficiency in young bulls can be achieved without negatively impacting seminal characteristics associated with fertility.