Effect of dietary supplementation with lipids of different unsaturation degree on feed efficiency and milk fatty acid profile in dairy sheep

Abstract

Simple Summary: The use of fats derived from palm is becoming very common in dairy sheep farms to increase the energy concentration of the diet and therefore the milk production. However, these fats may negatively affect the nutritional quality of milk, whereas feeding unsaturated oils may improve milk fatty acid profile. In this regard, our results in dairy sheep suggested that using palm fat had no evident disadvantage in terms of milk fatty acid composition compared with a diet without supplementation. Nevertheless, it had no positive effects on production or indicators of feed efficiency (for example, milk yield per unit of feed consumed). By contrast, supplementation with oils rich in unsaturated fatty acids (specifically olive oil and soybean oil) improved milk fatty acid profile, with stronger effects with the use of the most unsaturated fat: soybean oil. For example, the latter oil induced the greatest increases in fatty acids with potentially positive effects on human health (e.g., conjugated linoleic acid). In addition, from a practical point of view, the use of soybean oil might also be recommendable to improve the amount of milk produced per unit of feed consumed, compared with the use of palm fat. Abstract: Lipids of different unsaturation degree were added to dairy ewe diet to test the hypothesis that unsaturated oils would modulate milk fatty acid (FA) profile without impairing or even improving feed efficiency. To this aim, we examined milk FA profile and efficiency metrics (feed conversion ratio (FCR), energy conversion ratio (ECR), residual feed intake (RFI), and residual energy intake (REI)) in 40 lactating ewes fed a diet with no lipid supplementation (Control) or supplemented with 3 fats rich in saturated, monounsaturated and polyunsaturated FA (i.e., purified palmitic acid (PA), olive oil (OO), and soybean oil (SBO)). Compared with PA, addition of OO decreased milk medium-chain saturated FA and improved the concentration of potentially health-promoting FA, such as cis-9 18:1, trans-11 18:1, cis-9 trans-11 CLA, and 4:0, with no impact on feed efficiency metrics. Nevertheless, FA analysis and decreases in FCR and ECR suggested that SBO supplementation would be a better nutritional strategy to further improve milk FA profile and feed efficiency in dairy ewes. The paradox of differences observed depending on the metric used to estimate feed efficiency (i.e., the lack of variation in RFI and REI vs. changes in FCR and ECR) does not allow solid conclusions to be drawn in this regard.