Effect of Hemp Seed Oil on Milk Performance, Blood Parameters, Milk Fatty Acid Profile, and Rumen Microbial Population in Milk-Producing Buffalo: Preliminary Study

Vegetable oils rich in unsaturated fatty acids have been shown to improve animal health and enrich milk with functional fatty acids in various studies. This study investigates the effects of dietary supplementation with hemp seed oil (HSO), a native vegetable oil from the "longevity village" of Bama (Guangxi, China), on the milk performance, milk fatty acid composition, blood indicators, and rumen bacterial community of milk-producing buffalo. Seventeen healthy, four-year-old, crossbred, milk-producing buffaloes with the same parity (three), as well as similar body weights (BW = 580 ± 25 kg), number of days producing milk (DIM, 153 ± 10 d), and milk yields (8.56 ± 0.89 kg/d) were divided into three groups (<i>n</i> = 6, 5, and 6) and assigned to the following diets: (1) no HSO supplement (H0, <i>n</i> = 6), (2) a supplement of 100 g/d of HSO (H1, <i>n</i> = 5), and (3) a supplement of 200 g/d of HSO (H2, <i>n</i> = 6). The total experimental period was 42 days (including a 14-day adaptation period and a 28-day treatment period). The data were statistically analyzed by repeated measures analysis of variance. The results showed that compared to that of no HSO supplement group, the dry matter intake (DMI) showed a decreasing tendency (<i>p</i> = 0.06), while feed efficiency and rumen fermentation remained similar across all the groups (<i>p</i> > 0.05) with dietary HSO supplementation. Moreover, with dietary HSO supplementation, the total antioxidant capacity (T-AOC) (<i>p</i> = 0.05) and catalase (CAT) (<i>p</i> < 0.01) and glutathione peroxidase (GSH-Px) (<i>p</i> = 0.02) contents in the serum were greatly increased, with the highest levels observed in the H2 group (increased by 1.16 U/mL, 1.15 U/mL, and 134.51 U/mL, respectively). In contrast, the malondialdehyde (MDA) content was significantly decreased with dietary HSO supplementation (<i>p</i> = 0.02) and was the lowest in the H1 group (decreased by 0.72 nmol/mL). The high-density lipoprotein cholesterol (HDL-C) content in the blood showed an increasing tendency with dietary HSO supplementation (<i>p</i> = 0.09). Moreover, with dietary HSO supplementation, the proportions of C18:0 (<i>p</i> = 0.02), C18:1n9t (<i>p</i> = 0.02), C18:2n6c (<i>p</i> = 0.02), C18:3n3 (<i>p</i> < 0.01), C18:2n9c (<i>p</i> = 0.04), omega-3 (<i>p</i> = 0.02), and omega-6 (<i>p</i> = 0.02) were significantly increased, with the highest levels observed in the H2 group (increased by 5.29 g/100 g FA, 1.81 g/100 g FA, 0.55 g/100 g FA, 0.14 g/100 g FA, 0.75 g/100 g FA, 0.17 g/100 g FA, and 0.56 g/100 g FA, respectively). Additionally, rumen <i>Acetobacter</i> abundance was significantly affected by HSO addition (<i>p</i> = 0.03), with rumen <i>Acetobacter</i> abundance decreasing in the H1 group (by 0.55%) and increasing in the H2 group (by 0.73%). These results suggest that adding HSO to milk-producing buffalo diets does not affect feed efficiency or rumen fermentation, although it decreases the DMI. Meanwhile, it can improve the nutritional quality of milk, enhance the antioxidant status, and regulate blood lipid metabolism in milk-producing buffaloes.