The Safety Evaluation of Branched-Chain Fatty Acid Derived from Lanolin and Its Effects on the Growth Performance, Antioxidant, Immune Function, and Intestinal Microbiota of C57BL/6J Mice

<b>Background/Objectives</b>: Branched-chain fatty acids (BCFAs) exhibit a range of biological activities; however, their limited natural abundance and high cost have constrained in vivo research. Lanolin represents a promising source for enriching BCFAs. Nevertheless, the in vivo application, safety, and dose-effect relationship of BCFAs derived from lanolin (BCFAs-DFL) remain unassessed. <b>Methods</b>: In this study, the acute toxicity in C57BL/6J mice was first evaluated for 7 days by a single oral administration of 5000 mg/kg BW of BCFAs-DFL. Subsequently, 40 mice were divided into four groups (control group, low dose of 100 mg/kg BW, medium dose of 300 mg/kg BW, and high dose of 600 mg/kg BW) and were continuously administered by gavage for 28 days to study the effects of BCFAs-DFL on the growth, blood biochemistry, intestinal morphology, and intestinal flora of the mice. <b>Results</b>: In the acute toxicity test, BCFAs-DFL exhibited no lethality or abnormalities in mice, indicating its non-toxic nature. Throughout the 28-day trial, mice in the medium- and high-dose groups experienced a notable decrease in average daily feed intake (<i>p</i> < 0.05), yet their weight gain remained unaffected (<i>p</i> > 0.05). Hemoglobin and hematocrit levels declined in the high-dose group (<i>p</i> < 0.05). Conversely, serum aspartate aminotransferase and total bilirubin levels escalated in the medium- and high-dose groups, while triglycerides and urea nitrogen levels decreased (<i>p</i> < 0.05). The serum's total antioxidant capacity and immunoglobulin levels (IgA, IgG) rose in proportion to the dosage (<i>p</i> < 0.05). BCFAs-DFL notably enhanced the villus height of the jejunum and ileum in mice (<i>p</i> < 0.05). Gut microbiota analysis indicated no significant impact on overall α and β diversity. <b>Conclusions</b>: The 28-day intervention revealed that BCFAs-DFL can modulate feeding behavior, TG, T-AOC, and immunoglobulin levels in mice. Additionally, it promotes the development of intestinal villi. Based on various indicators, a dosage of 100 mg/kg BW effectively induces beneficial metabolic regulation, such as the reduction of triglycerides, without causing a burden on liver metabolism. This dosage may represent a more suitable application for potential use.