Lipid metabolic differences in cows producing small or large milk fat globules: Fatty acid origin and degree of saturation

摘要

This study compared cows that consistently producemilk with small (volume-weighted mean diameter of2.92–3.83 μm, with an average diameter of 3.29 μm) orlarge (volume-weighted mean diameter of 4.58–5.67 μm,with an average diameter of 4.92 μm) milk fat globule(MFG) size distributions in terms of the fatty acid (FA)composition of the MFG core. Selected cows fell intothe respective size group over at least 3 independentmeasurements, including an observation period beforethe experiment. Further selection criteria were similarmilk production traits between cows (milk yield, fatyield, fat/protein ratio) and established lactation (>50d in milk). However, the selected groups differed in parity(parity 1–3 and 3–5 in the small and large MFGgroups, respectively), and the small MFG group was anaverage of 25 d in milk later in their lactation period.All cows were under the same nutritional managementand environmental conditions. Here, we show that cowswith the small or large MFG phenotype differed intheir lipid metabolism in terms of the FA compositionof the MFG core. Our results indicate that cows withthe small MFG phenotype produced milk with higherconcentrations of unsaturated FA despite being fed thesame diet. We suggest that this characteristic of thesmall MFG phenotype is the result of increased uptakeof long-chain FA from the blood circulation. A relationshipbetween the degree of unsaturation and MFG sizewas also identified in preliminary studies across otherspecies—namely, camels, sheep, and goats. These findingsshow the potential for on-farm selection of cows(and potentially other dairy species) based on MFGsize to produce milk with improved nutrient composition.This could lead to purpose-specific separation ofmilk based on MFG size and FA profile, both known toalter the technological properties of milk.