Effects of rumen-protected choline supplementation on lactation performance of dairy cows: A systematic review and...

Peripartum supplementation of rumen-protected choline has been shown to improve cow health and milk production by improving liver function through a reduction in hepatic lipidosis. However, the optimal dose range remains undetermined. To evaluate the effects of supplemented choline chloride on lactation performance and health of dairy cows, a systematic review and dose-response meta-analysis were conducted. This meta-analysis followed the preferred reporting items for systematic reviews and meta-analyses guidelines and used the population (dairy cows), intervention (choline supplementation), comparison (control group vs. choline supplementation), and outcome framework to select studies on dairy cows supplemented with choline. A total of 30 studies from 19 articles and 1 dissertation, identified through Web of Science, Scopus, Google Scholar, and PubMed, were included. The analysis focused on DMI, milk yield and composition, BW, and BCS. Study quality and risk of bias were evaluated using systematic review center for laboratory animal experimentation's risk of bias tool. A 1-stage random-effects meta-analysis with a restricted cubic spline model was employed to assess dose-response relationships, with REML used for variance estimation. Subgroup and sensitivity analyses were performed to address heterogeneity and robustness, and publication bias was assessed using funnel plots and adjusted with the trim-and-fill method. This meta-analysis showed the significant effects of choline supplementation on intake and lactation performance of dairy cows. Optimal DMI was reached at 13 to 14 g/d, resulting in an increase of 0.48 kg/d (95% CI: 0.10, 0.87), whereas milk yield peaked at 13 g/d, with an increase of 1.29 kg/d (95% CI: 0.17, 2.41). A significant dose-response relationship for 3.5% FCM yield was observed across 21 trials, with efficacy significantly increasing steadily between 15 and 21 g/d, and a predicted mean difference of 2.19 kg/d at 21 g/d (95% CI: 0.48-3.90). Milk fat yield increased significantly by 0.09 kg/d at a dose of 24 g/d (95% CI: 0.01, 0.17), whereas milk protein yield improved significantly in the 13 to 20 g/d range despite considerable heterogeneity (>50%). A subgroup analysis showed that factors such as parity and level of milk yield had no significant effect on milk protein yield. However, the effects on milk protein yield were only significant in studies conducted between 2012 and 2024 compared with studies conducted between 2000 and 2011. In addition, choline chloride supplementation fed postpartum after 21 DIM had a significant effect compared with feeding before 21 DIM, and the commercial brand of rumen-protected choline also had a significant effect on milk protein yield. No significant effects were observed on milk composition (fat, protein, lactose), MUN, BCS, or prepartum BW, although overall BW increased significantly at a choline chloride dose of 11 g/d, reaching a peak of 12.5 kg (95% CI: 0.01, 24.96). Based on the results, an optimal total choline chloride dose of 13 to 14 g/d is recommended to increase total milk yield. Overall, these results suggest that choline chloride supplementation improves nutrient utilization and increases milk production in dairy cows.