This study evaluated the effects of emulsified oil (EO) and lysophospholipid (LPL) supplementation on early-lactating Holstein cows under heat stress. Fifteen multiparous Holstein cows were assigned to a completely randomized design for ۷۰ days with three dietary treatments: ۱) a basal diet containing (dry matter basis; DM) ۱.۵۲% pure fat powder (PFP; control); ۲) the basal diet supplemented with ۰.۱۵% LPL (partially replacing PFP); and ۳) the basal diet supplemented with ۱.۵۲% EO (completely replacing ۱.۵۲% PFP). Dry matter intake and milk yield were recorded daily. Milk and blood samples were collected at the end of the experiment. The average temperature-humidity index (THI) during the study was ۷۱. Dietary treatments did not significantly affect DM intake or average milk yield (P>۰.۰۵). Milk fat yield was significantly greater in the EO group compared with the LPL and PFP groups (P<۰.۰۵). Supplementation with EO increased milk yield during weeks ۲, ۳, and ۶ relative to PFP (P<۰.۰۵). Cows receiving EO exhibited lower proportions of C۱۶:۰ and higher proportions of C۱۸:۱, C۱۸:۲, and C۱۸:۳ fatty acids (P<۰.۰۵). Plasma glucose concentrations were elevated in cows fed EO compared with the other treatments (P<۰.۰۵), whereas cholesterol concentrations were reduced by both EO and LPL compared with PFP (P<۰.۰۵). Emulsified oil supplementation significantly decreased plasma low-density lipoprotein (LDL),
β-hydroxybutyric acid (BHBA), and
non-esterified fatty acids (NEFA) levels relative to PFP (P<۰.۰۵), while plasma albumin concentrations were higher in the LPL and PFP groups than in EO (P<۰.۰۵). In addition, EO supplementation significantly reduced plasma creatine phosphokinase activity compared with PFP (P<۰.۰۵). Overall, EO supplementation enhanced milk fat yield, improved milk unsaturated fatty acid profile, and optimized blood metabolites, indicating its potential to support metabolic efficiency and lactational performance in early-lactating Holstein cows under heat stress condition.
