Leucine as a feed additive enhances the concentration of branched-chain fatty acids in cow's milk

The feasibility of exogenously adding leucine (Leu) to produce branched-chain fatty acids (BCFA) enriched milk by simulating rumen fermentation in vitro and feeding study in vivo was investigated. Treatments for in vitro fermentation trial were control, 0 mM of Leu (CON1); 1 mM of Leu (LEU1); 2 mM of Leu (LEU2); and 4 mM of Leu (LEU4). For the in vivo feeding study, 20 Holstein dairy cows were allocated to 2 treatments: control, 0 g/cow/d Leu (CON2; n = 10); and 80 g/cow/d Leu supplementation (LEU80; n = 10). The concentration of BCFA including iso -13:0 ( P < 0.01), iso -15:0 ( P < 0.01), anteiso -15:0 ( P < 0.01), iso -16:0 ( P = 0.02) and total BCFA ( P = 0.01) in fermentation liquid increased linearly with increasing Leu inclusion rates. According to 16S rRNA sequencing, the abundances of Firmicutes ( P = 0.04), Clostridia ( P = 0.03) and Saccharofermentans ( P = 0.04) in the LEU4 group were higher compared to CON1 group. Pathway analysis revealed that the differential metabolites are primarily associated with lysine degradation, glycerophospholipid metabolism, purine metabolism, trothane, piperidine and pyridine alkaloid biosynthesis. In the in vivo trial, the result showed that Leu supplementation increased the concentration of BCFA in milk, including iso -13:0 ( P = 0.01), iso -15:0 ( P = 0.02), anteiso -15:0 ( P = 0.01), iso -16:0 ( P = 0.01), iso -17:0 ( P = 0.02), and anteiso -17:0 ( P < 0.02). Compared to the CON2 group, the concentration of total BCFA was increased by 26.2 % (891 μg/mL vs 706 μg/mL). In conclusion, supplementation of dairy cow's diets with Leu can enrich BCFA in milk. This can be useful for the design and development of functional dairy products that are beneficial for human health. • Leucine increased branched-chain fatty acids (BCFAs) concentration in rumen. • Firmicutes may be dominant phylum that utilizes leucine to synthesize BCFAs. • Leucine increased BCFAs concentration in milk. • The study will be useful to produce enriched BCFA milk products.