Milk fat is secreted mainly in the form of fat globules (MFG) from the mammary glands of female mammals into the milk. The MFG particle size ranges from 0.2 to 15.0 μm. MFG sizes can affect the health of newborns and the physical and chemical properties of dairy products. As the size of MFG is determined by intracellular lipid droplets during the secretion of mammary epithelial cells, the regulation factors of lipid droplet size include intracellular triglyceride (TG) level and enzymes involved in the synthesis and hydrolysis of TG, enzyme, membrane phospholipid, and lipid droplet fusion, etc. This review mainly describes the synthesis and structure of MFG, the regulation of MFG particle size and its impact on human nutrition, dairy processing and lipid droplet size fusion, which will provide reference for the application of milk fat globule size.

To investigate the effect of dietary nano selenium (Se) on the level of Se in cow’s milk, ten healthy Holstein dairy cows were divided into two groups of 5 animals each, i.e., control and test groups. The control group was fed a basal diet and the test group was additionally given 15 g of dietary nano selenium each day for each cow. The results indicated that despite having no significant effect on the contents of milk fat, protein and lactose (P > 0.05), dietary nano selenium significantly increased the level of Se concentration compared with (P < 0.05). The concentration of milk Se was increased gradually with prolonged dietary supplementation, reaching 29.4 μg/L on day 30 compared to only 16.6 μg/L for the control group (P < 0.05). From these results it can be concluded that dietary supplementation with nano-Se could increase the concentration of Se in milk.