Evaluation of the residual feed intake on carcass and meat quality traits of Nellore bulls: a biochemical and molecular approach.

This study aimed to compare dry matter intake (DMI), feed efficiency, carcass traits, and meat quality between feedlot Bos indicus cattle with divergent residual feed intake (RFI). Ninety-six Nellore bulls (initial body weight 362.45 ± 25.6 kg, aged 24-26 months) underwent a 70-d feed efficiency test in a group-pen system equipped with individual feed intake and weight gain monitoring. After classification into low (efficient) and high (inefficient) RFI groups (-0.54 vs. 0.59 kg/d, respectively), the animals were slaughtered at a final body weight of 520 ± 31 kg after 120 days of feeding. Differences (P < 0.05) were observed between low and high RFI groups for DMI (9.14 vs. 10.42 kg/d; P < 0.05), and feed conversion (6.06 vs. 6.74 kg/kg; P < 0.05), and RFI (P < 0.05). Carcass traits differed (P < 0.05) between low vs. high RFI experimental groups (dressing percentage [DP]: 54.44 vs. 53.23 %; P < 0.05 and backfat thickness [BFT]: 4.75 vs. 5.61 mm; P < 0.05), with a tendency towards greater ribeye area (REA) in the low RFI group (86.05 vs. 82.91 cm²; P = 0.07). Less intramuscular fat content (IMF = 1.43 vs. 1.75 %; P < 0.05) and myofibrillar fragmentation index (MFI = 27.04 vs. 32.15 at 5 days of aging; and 53.01 vs. 68.3; P < 0.01 at 15 days of aging) were reported in low RFI cattle, while other parameters such as pH, color (L*, a*, b*), cooking loss, shear force (WBSF), or lipid oxidation did not differ (P > 0.05) between RFI groups. After 15 days of aging, there was an increase in L* (P < 0.01) and a decrease in pH, a*, b*, and WBSF (P < 0.01) regardless of RFI group. Sensory analysis revealed smaller scores (P < 0.05) for juiciness (55.3 vs. 58.91) and overall acceptability (58.3 vs. 63.6) in low RFI cattle. Lipidomic analysis identified a difference in 60 lipid species (P < 0.05) between groups, including diacylglycerols, free fatty acids, phosphatidylcholines, phosphatidylethanolamines, sphingomyelins, and triacylglycerols. Nellore bulls with low RFI had leaner carcasses with less backfat and tended to have larger ribeye areas. Their meat contained less intramuscular fat and more drip loss, which negatively impacted sensory quality as perceived by consumers. This study is the first to characterize the lipidome of beef cattle with divergent RFI, revealing lipid classes linked to mitochondrial function and lipid storage, which may help explain differences in feed efficiency, carcass, and meat quality traits.