Effects of source of forage and level of concentrate on chewing activity and milk production response in late lactation cows

Four cannulated Holstein cows in late lactation were used in a 4 × 4 Latin square design experiment to determine the effects of forage source with different NDF concentrations and level of concentrate on chewing activity and milk production. Diets were 65% first-cut alfalfa silage with 54% NDF and 35% concentrate, 50% alfalfa and 50% concentrate, 65% bromegrass silage with 65.5% NDF and 35% concentrate and 50% bromegrass silage and 50% concentrate. Diets were fed in 2 × 2 factorial design (silage sources, alfalfa vs. bromegrass and two levels of concentrate, 35 vs. 50%). Dry matter intake averaged 15.2 kg d−1 and was not affected by either forage source or level of concentrate. Intake of NDF was lower for the cows fed the alfalfa-based diet vs. bromegrass silage but the level of concentrate did not affect NDF intake. Time spent eating was not affected by either forage source or concentrate level of the diet. Time spent eating and ruminating kg−1 NDF intake was higher for cows fed alfalfa-based diets than for cows fed the bromegrass-based diets. Total chews g−1 NDF intake tended (P = 0.06) to decrease when cows were fed bromegrass-based diets but eating and ruminating chews g−1 NDF intake were not affected by source of forage or level of concentrate in the diet. Diets with either alfalfa or bromegrass had no effect on daily yields of milk, FCM, fat, protein and lactose. Diets with 50% concentrate increased milk and FCM yields by 11 and 14%, respectively. Fat and lactose yields were also increased by 17 and 11% in cows fed diets with the higher concentrate level. Results suggest that chewing activities during eating and ruminating phases of the eating cycle adjusted for DMI may decrease with increased concentrate level and are not affected by source of forage in the diet. However, chewing activities adjusted for NDF intake are influenced by source of forage but not by level of concentrate in the diet. The results also suggest that yields of both milk and milk components in late lactation cows are influenced by level of concentrate in the diet, while only milk components are affected by source of forage. Key words: Dairy cattle, chewing activity, forage, milk production