73 Effects of Fatty Acids Sources and Lysophospholipids on Nutrient Digestibility in Lactating Cows

Abstract Fatty acids (FA) are a common supplement for lactating cows to increase energy supply, potentially improving feed efficiency and milk and milk fat yields. However, different FA can cause varying responses probably because of different FA digestibility and interactions with other nutrients (e.g., fibers). Lysophospholipids (LPL) are natural emulsifiers and LPL as a feed additive have shown increases in FA digestibility and nutrient absorption in non-ruminant animals. This study aimed to investigate the effects of FA sources with LPL supplementation on nutrient digestibility in lactating cows. Mid-lactation cows (n = 48) were allocated into 12 blocks, and cows in each block were randomly assigned to the following dietary treatments:1) a diet with a FA supplement [1.8% of dietary dry matter (DM)] mainly containing palmitic acid (PA); 2) the PA diet with LPL (0.003% of dietary DM); 3) a diet with a FA supplement (1.8% of dietary DM) mainly containing stearic acid (SA); and 4) the SA diet with LPL (0.003% of DM). The experiment was conducted for 6 weeks, and spot samples of feces and urine were collected over 3 days (every 3 hours within a 24-hour cycle) during the last week of the experiment to determine nutrient digestibility and utilization. Data were analyzed using the mixed model with FA source, LPL, and their interaction as fixed effects and block as a random effect. The digestibility of DM, organic matter, and crude protein were not affected by the FA source and no interaction between FA and LPL was observed. However, PA had greater neutral detergent fiber (NDF) digestibility (41.4 vs. 38.8%; P = 0.04) than SA with no interaction between the FA source and LPL. In addition, as expected, PA decreased (P < 0.01) the digestibility of 16-carbon FA compared with SA due to the greater C16:0 supply, and SA decreased (P < 0.01) that of 18-carbon FA compared with PA due to the greater C18:0 supply. Supplementation of LPL did not affect digestibility of DM, OM, CP, and NDF, but increased total FA digestibility (64.7 vs. 60.5%; P = 0.02) compared with no LPL. In addition, LPL increased 18-carbon FA digestibility (68.2 vs. 74.1%; P < 0.01) compared with no LPL. An interaction between LPL and FA was observed for 16-carbon digestibility because LPL increased 16-carbon digestibility with SA but not with PA. In conclusion, PA supplementation improved fiber digestibility compared with SA, which could be a factor for increased productivity (e.g., milk fat). Supple