Bovine milk fatty acid and triacylglycerol composition and structure differ between early and late lactation influencing milk fat solid fat content

Milk samples were collected in early lactation (8–14 days in milk; DIM) and late lactation (199–326 DIM) from 11 cows to assess the differences in bovine milk fatty acid (FA) and triacylglycerol (TAG) composition, FA positional distribution in the TAG structure, and milk solid fat content (SFC). Cows in early lactation that were in negative energy balance, mobilised C16:0, C18:0, and C18:1cis9 from their body fat stores, increasing the concentrations of these FA in milk fat. These high concentrations of C18:0 and C18:1cis9 enhanced the synthesis of high molecular weight TAG and decreased milk fat SFC in early lactation. For both lactation stages, alterations in the total FA concentrations in the TAG structures resulted in changes in the abundances and the proportions of the FA at the sn-2 and sn-1 (3) positions in the TAG structure, yet without affecting the main esterification preferences of the FA.