Choline: Is there a need in the lactating dairy cow?

Recent developments in nutrition have established that choline is an essential nutrient for mammals when a sufficient supply in methionine and folates is not available in the diet. Vitamin B12 is also involved in this process. In adult ruminants, choline is extensively degraded in the rumen; for this reason dietary choline contributes insignificantly to the choline body pool and methyl group metabolism is generally conservative with a relatively low rate of methyl catabolism and an elevated rate of de novo synthesis of methyl groups via the tetrahydrofolate system. In dairy ruminants, the dietary availability of choline is nearly non-existent, but the output of methylated compounds in milk is high while methionine as well as other sources of methyl groups are likely to be in short supply, especially at the onset of lactation. Based on those observations, the effects of rumen-protected choline (RPC) supplementation to transition cows was studied in two trials. Results obtained suggested that a greater choline availability can improve not only milk production efficiency, but also lipid and methyl group metabolism in transition dairy cows. RPC also increased plasma α-tocopherol, suggesting a novel choline-vitamin E interaction. However, the exact mechanisms underlying these findings are unclear, and choline requirements in dairy cows are still unknown. This indicates that further studies under different feeding conditions are needed.