Effects of nonstructural carbohydrates and source of cereal grain in high concentrate diets of dairy cows

Five primiparous and 5 multiparous Holstein cows were used in an experiment with a double 5 x 5 Latin square design to evaluate the effects of lowering the concentration of nonstructural carbohydrates in high grain diets on intake, chewing activities, digestibility, and yield and composition of milk. Cows received diets consisting of 30% barley silage (dry matter basis) and one of five isocaloric concentrates containing corn, hull-less barley, or barley, ranging in the percentage of nonstructural carbohydrates from 24 to 42%. Diet did not affect the dry matter intake (DMI) of primiparous cows. However, for multiparous cows, as the concentration of nonstructural carbohydrates in the corn diets was lowered from 34 to 30%, DMI increased from 16.3 to 18.9 kg/d (2.66 to 3.07% of body weight), and, as the concentration of nonstructural carbohydrates in the barley diets was lowered from 29 to 22%, DMI increased from 19.6 to 21.0 kg/d (3.09 to 3.19% of body weight). For both groups of cows, a reduction in the nonstructural carbohydrates in either the corn or barley diets had minimal effects on milk yield, fat-corrected milk yield, fat content, and protein content, except that the fat content of milk from younger cows fed barley diets was lowered (2.70% vs. 2.30%). For diets formulated at similar concentrations of nonstructural carbohydrates, grain source had no effect on DMI or digestible DMI, but milk yield was lower for cows fed the diet containing hull-less barley (25.2 kg/d) than for cows fed the diets containing corn (26.8 kg/d) or barley (28.1 kg/d). When the concentrations of nonstructural carbohydrates in high grain diets were reduced, feed intake was enhanced, but the relationship between the concentration of nonstructural carbohydrates and performance was not consistent. Differences in ruminal availability of carbohydrates need to be accounted for when diets are formulated on the basis of nonstructural carbohydrates using a range of cereal grains.