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 x 4 L atin square design experiment to determine the effects of forage sourc e with different NDF concentrations and level of concentrate on chewin g activity and milk production. Diets were 65% first-cut alfalfa silag e with 54% NDF and 35% concentrate, 50% alfalfa and 50% concentrate, 6 5% bromegrass silage with 65.5% NDF and 35% concentrate and 50% bromeg rass silage and 50% concentrate. Diets were fed in 2 x 2 factorial des ign (silage sources, alfalfa vs. bromegrass and two levels of concentr ate, 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 N DF was lower for the cows fed the alfalfa-based diet vs. bromegrass si lage but the level of concentrate did not affect NDF intake. Time spen t eating was not affected by either forage source or concentrate level of the diet. Time spent eating and ruminating kg(-1) NDF intake was h igher for cows fed alfalfa-based diets than for cows fed the bromegras s-based diets. Total chews g(-1) NDF intake tended (P = 0.06) to decre ase when cows were fed bromegrass-based diets but eating and ruminatin g chews g(-1) NDF intake were not affected by source of forage or leve l 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 1 1% in cows fed diets with the higher concentrate level. Results sugges t that chewing activities during eating and ruminating phases of the e ating cycle adjusted for DMI may decrease with increased concentrate l evel and are not affected by source of forage in the diet. However, ch ewing activities adjusted for NDF intake are influenced by source of f orage but not by level of concentrate in the diet. The results also su ggest that yields of both milk and milk components in late lactation c ows are influenced by level of concentrate in the diet, while only mil k components are affected by source of forage.