369 Effect of Diet, Rumen Fermentation Parameters and Their Combination on Predicting Milk Production

The objective of this meta-analysis was to explore variability in milk production associated with rumen fermentation parameters and diet characteristics. Data were extracted from 138 journal articles and used to derive 6 models to predict MY. Each model considered a different set of independent variables, including rumen fermentation parameters (R), diet (D) and their combination (R+D), with or without interactions with rumen pH. Rumen fermentation parameters included total volatile fatty acid (VFA) concentration, molar proportions of major and minor VFA, rumen pH and ammonia nitrogen, and diet variables included dry matter intake (DMI) dietary percentages of dry (DM) and organic matter (OM), crude protein, neutral (NDF) and acid detergent fiber (ADF), ether extract, and starch. Linear mixed-effects models weighted by the inverse of the standard error were employed. Models were compared based on concordance correlation coefficients after removing random study effects (CCC). The MY models using D, R, D+R and D*pH performed similarly with CCC values ranging from 0.63 to 0.65. Models including an interaction with rumen pH were superior at explaining variation within the data (CCC: 0.75 to 0.76). The Final model derived using D, consisted of DMI and ADF. Molar proportions of acetate and propionate and DMI were in the final model based on R. The interaction between starch and pH remained in the final D*pH model along with DMI, DM, NDF and pH. From these models, we can conclude that rumen pH is an important moderator explaining variability in the associations among diet, rumen VFA, and milk production.