Recent knowledge is presented on the composition of ruminant milk fat fractions and the nutritional strategies known to alter their amount. The development of lipidomic and proteomic analyses has allowed for the characterization of minor components, such as proteins, liposoluble vitamins, and phospholipids of the milk fat globule (MFG), in addition to the triacylglycerols (TAG), which are the major constituents of the MFG core. Few differences in these components among ruminant species exist, and they have been outlined mainly on the fatty acids (FA) profile of the TAG, whereas comparative data are still lacking on vitamins and proteins. The effects of dietary treatments enriched in n‐3 polyunsaturated FA (PUFA) on the composition of the milk fat fraction are explored. In particular, pasture and plant oilseeds increase milk n‐3 PUFA and cis‐9,trans‐11 CLA and decrease saturated FA, whereas data with new feed resources, such as algae, are still rare. The peculiarities of the response of the milk fat to diets that induce a milk fat depression in cows but in lesser extent in small ruminants are described. The potential effects of polar lipids, proteins, and liposoluble vitamins of the MFG on human health are reviewed, highlighting the nutraceutical properties of milk. Practical Applications: This review provides an overview of the different components of the milk fat fraction in ruminant species and on nutritional strategies to alter their amounts to improve the nutritional quality of milk. Furthermore, this review presents recent data on species peculiarities of the milk fat fraction composition and of its response to nutritional factors, which offers a promising model to identify news levers of regulation of this fraction and foster the identification of new feeding strategies to better control milk fat composition and feed efficiency. This review synthesizes data on the composition of the milk fat fraction in ruminant species, reports advances in nutritional strategies to alter their amounts and species‐specific responses to nutrition, as well as the potential effects on human health of the major and minor components of this fraction.

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A better knowledge of the bovine milk proteome and its main drivers is a prerequisite for the modulation of bioactive proteins in milk for human nutrition, as well as for the discovery of biomarkers that are useful in husbandry and veterinary medicine. Milk composition is affected by lactation stage and reflects, in part, the energy balance of dairy cows. We aggregated the cow milk proteins reported in 20 recent proteomics publications to produce an atlas of 4654 unique proteins. A multistep assessment was applied to the milk proteome datasets according to lactation stages and milk fractions, including annotations, pathway analysis and literature mining. Fifty-nine proteins were exclusively detected in milk from early lactation. Among them, we propose six milk proteins as putative biomarkers of negative energy balance based on their implication in metabolic adaptative pathways. These proteins are PCK2, which is a gluconeogenic enzyme; ACAT1 and IVD, which are involved in ketone metabolism; SDHA and UQCRC1, which are related to mitochondrial oxidative metabolism; and LRRC59, which is linked to mammary gland cell proliferation. The cellular origin of these proteins warrants more in-depth research but may constitute part of a molecular signature for metabolic adaptations typical of early lactation.