Response of early lactation Holstein cows to partial replacement of neutral detergent soluble fibre for starch in diets varying in forage particle size

This study investigated the effects of partial replacement of neutral detergent soluble fibre (NDSF) for starch in diets varying in particle size (PS) of alfalfa hay on chewing activities, ruminal fermentation, nutrient digestibility and performance of early lactation dairy cows. Eight multiparous Holstein cows (66±5 d in milk; 42.9±3.1 kg milk/d) were used in a replicated 4×4 Latin square design with four 22 d periods with the last 8 d used for data collection. The experiment was a 2×2 factorial arrangement with 2 levels of NDSF (low=84 g/kg or high=118 g/kg diet dry matter) each combined with 2 PS (short=20 mm or long=40 mm) of alfalfa hay. Feeding short PS in combination with low level of NDSF increased intake of DM and OM (P<0.05). Total chewing time was not affected, however, total eating time and eating times spent per kg of DM and NDF consumed decreased when forage particle size was reduced (P<0.05). High NDSF diets increased total eating time and eating times spent per kg DM and NDF ingested and increased apparent digestibility of NDF (P<0.05). However, feeding high NDSF diet increased the OM digestibility only in long PS diet (P<0.05). Treatments did not affect ruminal pH; however, feeding short PS tended to increase total volatile fatty acid concentration, decreased molar proportion of acetate and increased that of propionate. Inclusion of NDSF decreased molar proportion of propionate and increased that of butyrate and decreased ruminal ammonia concentration (P<0.05). Milk yield and composition and milk energy output were similar among treatments. Results show that partial replacement of NDSF for starch increases nutrient digestibility, most notably for NDF, and maintains milk yield and composition of early lactation cows fed diets varying in forage PS.