Effects of feeding two rumen-protected choline sources during the transition period on performance and blood metabolites of Holstein dairy cows

This study evaluated the effects of two rumen-protected choline (RPC) sources supplemented to dairy cows from 21 d pre- to 35 d postpartum. Twenty-four multiparous Holstein cows were randomly assigned to three groups (n = 8/group): control (CON, unsupplemented TMR), RPC1 (TMR with 60 g/d lipid microencapsulated choline chloride 25%, Ruprocol®), and RPC2 (TMR with 25 g/d lipid-encapsulated choline chloride 60%, ReaShure®-XC). Both supplements were mixed with TMR and provided 15 g/d of choline chloride. From 36 to 70 d postpartum, all cows received unsupplemented TMR. The mixed model included fixed effects of treatment, time, and their interaction; nonorthogonal contrasts compared CON vs. RPC1 and CON vs. RPC2. Prepartum DMI tended to be lower in choline-supplemented cows, particularly in the RPC1 group, whereas postpartum DMI, BW, and BCS did not differ among treatments. RPC1 increased 3.5% fat-corrected milk compared to CON. Choline supplementation reduced plasma glucose and tended to increase non-esterified fatty acids and bilirubin at 3 d postpartum. Plasma paraoxonase was higher at 21 d relative to calving in RPC2 compared to RPC1 and CON, while ceruloplasmin was reduced in both RPC groups around calving compared to CON. Cows supplemented with RPC1 had significantly greater prepartum DMI efficiency relative to milk and energy-corrected milk yields during both supplementation and post-supplementation periods compared to CON. These findings suggest that RPC supplementation can improve milk yield and influence the immunometabolic profile of transition dairy cows, with effects varying depending on the protection technology used, highlighting the importance of optimising choline supplementation strategies.