Performance of lactating dairy cows fed varying amounts of soyhulls as a replacement for corn grain.

Fifteen multiparous Holstein cows averaging 112 d in milk were used in a replicated 5 x 5 Latin square to evaluate the incremental substitution of soyhulls for corn in the diet. Diets contained 23% alfalfa silage, 23% corn silage, and 54% concentrate on a dry matter basis. Pelleted soyhulls replaced corn in the concentrate to supply 0, 10, 20, 30, or 40% of the dietary dry matter. Dry matter intake decreased linearly as soyhulls replaced corn in the diet, but the major decrease in dry matter intake occurred when soyhulls provided 30 and 40% of the dietary dry matter. Intakes of both acid and neutral detergent fiber increased linearly as soyhulls increased from 0 to 40% of dietary dry matter. Production of milk tended to decrease when soyhulls supplied 40% of the dietary dry matter. Production of 3.5% fat-corrected milk, milk crude protein percentage and yield, milk urea N, and total solids yield were not affected by treatments. Production of true protein, but not percentage, tended to decrease by about 5% when soyhulls supplied 40% of the dietary dry matter. Increasing the percentage of soyhulls in the dietary dry matter increased linearly milk fat content and yield, and total solids content in milk. These data suggest that soyhulls can successfully supply up to about 30% of the dry matter intake of midlactation cows without depressing animal performance. Furthermore, replacing part of the corn with soyhulls in high grain diets may be viable when milk fat has a high monetary value or when soyhulls can be purchased at a more competitive price than grains on a nutrient content basis.