Effects of different palmitic and oleic acid ratios on intake, feeding behavior, digestibility, lactation performance and selected blood parameters in lactating Holstein cows

Abstract

This study evaluated the effects of varying ratios of palmitic acid (C16:0; PA, provided as free fatty acid) to oleic acid (cis-9 C18:1; OA, provided as calcium salts) on nutrient digestion, feeding behavior, milk production, and metabolic responses in lactating Holstein cows. Eight multiparous Holstein cows (mean parity = 3.2; days in milk (DIM) = 53 ± 9 d; BW = 577 ± 48 kg; milk yield = 39.2 ± 1.9 kg/d) were assigned to a duplicated 4 × 4 Latin square design with four treatment diets: (1) 100 % PA: 0 % OA (100PA:0OA), (2) 66 % PA:34 % OA (66PA:34OA), (3) 34 % PA:66 % OA (34PA:66OA), and (4) 0 % PA:100 % OA (0PA:100OA). All diets were isocaloric and iso-nitrogenous. Feed intake and feeding behavior were unaffected by PA-to-OA ratios. However, digestibility of NDF and total FA increased with higher OA levels, with the 0PA:100OA diet showing the highest NDF (513 g/kg DM) and FA digestibility (831 g/kg DM); higher OA levels were also associated with lower plasma free fatty acids and triglyceride concentrations. Milk yield, protein yield, and lactose yield were similar across treatments, but milk fat content decreased with higher OA levels. Milk FA composition showed reduced de novo FA synthesis and increased preformed FA with greater OA intake. Energy partitioning metrics, including net energy intake (167.2–171.7 MJ/d), milk energy output (103–106 MJ/d), maintenance energy (50.6–50.8 MJ/d) and energy balance (10.16–13.8 MJ/d), did not differ between treatments. Overall, these results indicate that increasing OA improves nutrient utilization and energy metabolism in dairy cows, primarily by reducing adipose tissue mobilization and improving metabolic efficiency, despite a concomitant reduction in milk fat concentration.