Systematic analysis of choline supplementation in dairy cows

Although, the choline requirement of dairy cows is still unknown, higher choline availability (by feeding rumen-protected choline, RPC) can improve milk production, suggesting that this substance may be a limiting nutrient in transition dairy cows. Based on these assumptions, we investigated the effects of rumen protected choline (RPC) administration on milk production and selected plasma metabolites (non-esterified fatty acids and beta-hydroxybutyrate) in 11 and 9 different studies, respectively, carried out between 1991 and 2008. Accordingly, 42 and 28 experimental groups for milk and plasma metabolites respectively, have been considered in the dataset. Mean and standard error data have been used in a regression model in which milk production response to RPC supplementation has been investigated. Dataset analysis indicated that although most of variability among experiments was related to treatments schedule, dry matter intake and dietary composition, these factors were also highly correlated. For this reason, and in order to avoid any redundancy in the model, our regression analysis included only RPC supplementation (control/treated) as fixed effect, while all the other variables have been considered as experimental effects and treated as random components in the mixed model, according to the idea that results of different experiments are affected by different experimental conditions. The data reviewed in this analysis are consistent with the fact that choline supplementation (5<20g/d) significantly (P<.05) increased milk yield in dairy cows. By contrast, effect of choline supplementation on plasma metabolites are inconclusive.