Effect of carbohydrates in grass silage-based diets on in sacco ruminal degradability of barley (Hordeum vulgare L. cv. Lomerit) grain ground to different particle sizes

The effect of carbohydrates included in grass silage-based diets on in sacco degradability of dry matter (DM), crude protein (CP), neutral detergent fibre (NDF) and cellulose (CE) of barley (Hordeum vulgare L. cv. Lomerit) grain ground to different particle sizes was studied using 3 ruminally cannulated cows. The measurements were carried out as a 3 × 2 Latin square design with treatments being carbohydrates in the concentrate portion of diets (starch in diet I vs. pectin in diet II vs. sucrose in diet III) and particle size of ground barley grain (1.0 vs. 5.7 mm). The diet synchronization index between N and energy supply during the day was an average of 0.8. The rumen degradability of barley grain compounds was influenced by the type of carbohydrates included in grass silage-based diets. Higher rumen degradation rates (P < 0.05) of barley CP, NDF and CE after 8 h of incubation and of CP and CE after 16 h of incubation were found in the rumen of cows receiving the diet containing sucrose compared with degradation rates found in the rumen of cows receiving the diet containing pectin or starch. The effective degradability of DM, CP, NDF and CE of barley grain in the rumen of cows receiving diets I, II and III was similar (77, 74, 39 and 41%, respectively). Replacing barley starch or beet pulp pectin with molasses sucrose in the grass silage-based diet resulted in the higher rate of barley CP, NDF and CE degradation after 8 h of incubation and of CP and CE after 16 h of incubation. It seems that the energy availability from carbohydrates affected the ruminal microbial activity as a consequence of the degradation rate of substrates. Higher (P < 0.01) rumen degradability of CP, NDF and CE after 2, 4, 8, 16 and 24 h of incubation was estimated for 1.0 mm particle size in comparison with that found for grain ground to 5.7 mm particle size, and the degradability of CP after 48 h of incubation was not different (P > 0.05). The degradability of barley grain CP, NDF and CE during incubation time was not influenced by the diet composition by particle size interaction (P > 0.05). The increase in barley grain particle size from 1.0 to 5.7 mm slowed down the rumen digestion of barley DM, CP, NDF and CE, probably due to restricted access to microbial digestion.