Milk production and composition, rumen fermentation parameters, and grazing behavior of dairy cows supplemented with different forms and amounts of corn grain

The objectives were to compare milk production and composition, change in body weight and body condition score, rumen fermentation parameters and grazing pat-terns by cows when supplemented with different forms and amounts of corn grain. In experiment 1, 36 Holstein cows were supplemented with either 6, 6, 6, or 4 kg/d of dry matter of high moisture corn, coarsely ground corn, finely ground corn, or high moisture corn in two equal daily feedings, respectively. Milk yield (30.3 kg/ d), milk protein (2.97%), and milk urea N (14.7 mg/ dl) were not different among treatments. Body weight change and body condition score change were similar (23.1 kg and −0.24) for the 10-wk study. During experi-ment 2, four rumen cannulated cows in midlactation were supplemented with 6 kg/d of dry matter from ei-ther coarsely ground corn or high moisture corn in two equal feedings after milking. After the p.m. milking, ruminal pH was measured and rumen fluid samples were collected from cows to determine ammonia N and volatile fatty acids at 0.5, 1, 2, 3,…8 h post-corn feeding during grazing. Ruminal pH values were similar for corn supplements, and, with one exception, were 6.0 or below between 5 and 8 h. Ruminal ammonia-N concen-trations reached a maximum at 7 h also. In experiment 3, 40 cows were observed for grazing behavior every 30 min for two consecutive days. Cows grazed an average of 6.4 h/d, 4.1 h in the afternoon and 2.3 h in the morn-ing. Milk yield, milk composition, change in body weight, and body condition were similar regardless of the type or amount of corn supplemented. (Key words: dairy cows, grazing cows, corn supplemen-tation, grazing behavior) Abbreviation key: CGC = coarsely ground corn, CSH = compressed sward height, FGC = finely ground corn