Effect of variation in proportion of cornmeal and steam-rolled corn in diets for dairy cows on behavior, digestion, and yield and composition of milk

Sixty-six lactating multiparous Holstein cows (113 +/- 46 DIM) housed in a free-stall facility were blocked and assigned randomly to one of three trea tments to evaluate the effects on animal performance from feeding cornmeal, cornmeal mixed with steam-rolled corn in a ratio of 1:1 on dry matter basi s, or steam-rolled corn. The only difference in the dietary ingredients was the type of corn, which was included in the total mixed ration (TMR) at 17 % of dry matter. The densities (g/L) of cornmeal and steam-rolled corn were , respectively, 635 and 553. Diets were fed as TMR and were formulated acco rding to the Cornell Penn Miner Dairy(R) nutrition model. The TMR consisted of 40% forage and 60% concentrate on dry matter basis. The first 2 wk of t he 8-wk study was a preliminary period, and data collected during this peri od were used as covariate in statistical analysis of production data collec ted during wk 6 to 8. Treatment diets were fed from wk 3 to 8. Total tract digestibilities of dry matter, organic matter, crude protein, starch, and n eutral detergent fiber were not significantly different among treatments. C ows fed TMR containing steam-rolled corn had higher body condition and rumi nated longer. However, feeding cornmeal and steam-rolled corn together did not improve dry matter and nutrient digestion, milk yield, 3.5% fat-correct ed milk yield, and percentage and yield of fat, crude protein, true protein , and lactose in milk, and milk urea nitrogen. In conclusion, feeding steam -rolled corn improved animal body condition and rumination. Partial or comp lete substitution of cornmeal by steam-rolled corn in diets for lactating d airy cows did not improve dry matter and nutrient digestion, milk yield, an d milk composition.