Combined Supplementation of Rumen-Protected Choline and Chromium Propionate as a Novel Feeding Strategy to Improve Lactation Performance, Immunity and Reduce Disease Incidence in Transition Dairy Cows.

Rumen protective choline (RPC) has drawn much attention for its significant impact on dairy cow metabolism and performance. Yet, its high cost hinders large-scale application. Chromium propionate (CrPr) is a cost-effective micronutrient supplement that enhances energy metabolism. However, the combined effect of RPC and CrPr on transition cows remains unclear. This study aimed to investigate the effects of RPC and CrPr co-supplementation versus RPC alone on health and lactation performance in transition cows. 120 transition Holstein cows were randomly divided into four groups (n = 30): Control (basal diet), CrPr (20 g/cow/day CrPr), RPC (60 g/cow/day RPC), and CrPr + RPC groups (20 g/cow/day CrPr + 30 g/cow/day RPC). The feeding lasted from 30 days prepartum to 21 days postpartum. Blood parameters (immune and oxidative markers) were assessed at -30, -21, 1, 14, and 21 days relative to calving. Milk was collected on days 7, 14, and 21 postpartum for its nutritional composition analysis. The results showed that RPC alone or in combination with CrPr significantly increased dry matter intake, rumination time, milk yield, and milk quality in transition cows and both treatments improved immune function (IgG, IgM) and antioxidant status (T-AOC, SOD, MDA, CAT). Importantly, all supplemented groups showed reduced incidence of ketosis, ruminal acidosis, milk fever, and mastitis during the first 150 lactation days. These findings demonstrate that CrPr+RPC co-supplementation achieved comparable effects to RPC alone in enhancing transition cow performance and health. This combined strategy offers a cost-effective alternative to improve metabolic health and farm profitability.