Effects of Prepartum Supplementation with Flaxseed and Black Soldier Fly Larvae Oils on Fatty Acid Composition and Lipid Quality Indices in Sheep Milk

The peripartum period in prolific ewes is associated with increased metabolic demands, and dietary lipid supplementation may increase the energy density of the prepartum diet. This study evaluated the effects of prepartum supplementation with alternative lipid matrices on the physicochemical characteristics and comprehensive fatty acid (FA) profiles of mature and transitional sheep milk. Thirty-two pregnant Olkuska ewes were randomly assigned to four cohorts (n = 8/group): Control (basal diet), flaxseed oil (low n-3/high n-6 variety; FO), black soldier fly larvae oil (BSFL oil), and Mix oil (2:1 ratio of FO to BSFL oil). Dietary treatments exerted no significant effects (p > 0.05) on transitional milk composition or lipid quality indices. In contrast, in mature milk, BSFL oil supplementation significantly increased milk fat content (6.09%) compared to the Control group (4.70%; p < 0.01). Furthermore, all oil treatments significantly reduced total saturated FAs (p < 0.01), while the BSFL oil and Mix oil supplementation significantly increased the monounsaturated FA fraction (p < 0.01). The differences, particularly the increase in cis-9, trans-11 CLA concentration and the significant reduction in both the atherogenic and thrombogenic indices (p < 0.01), were observed exclusively in mature milk. These findings suggest that the combination of sustainable insect lipids with high-linoleic plant oils may represent a viable strategy to transform sheep milk into a functional food with potential cardiovascular health benefits for consumers. These findings additionally indicate that prepartum lipid supplementation may exert a persistent carry-over effect into early lactation, influencing the fatty acid composition of mature sheep milk.