A meta-analysis and meta-regression of the impact of particle size, level, source and preservation method of forages on chewing behavior and ruminal fermentation in dairy cows

A meta-analysis of the impact of forage particle size (FPS) on chewing activity, rumen pH and volatile fatty acids (VFA) in dairy cattle was conducted following a search of the literature. A meta-regression was conducted to test the additional effect of forage level, source and preservation method on the heterogeneity of the results of FPS on the same target variables. A total of 42 papers and 86 trials with the change of FPS in the diet of dairy cattle were identified. Decreasing of FPS in the diet from an average of 10.0 ± 4.9–6.7 ± 4.11 mm lowered eating (P 500 g/kg forage). Forage preservation method was another source of variation accounting for high heterogeneity in the results of FPS in which eating (P = 0.03), rumination (P = 0.01), and total chewing (P = 0.02) activity decreased only in silage-based diets but not in hay-based diets. Total VFA concentration (P