Thirty-two lactating, multiparous Holstein-Friesian cows, each producing 16.3 ± 1.83 L of milk/d (average ± SD) with 582 ± 54.2 kg of BW and 203 ± 72.8 DIM were allocated to 3 groups balanced for mean milk yield, BW, and yields of fat and protein according to the method of Baird (1994). Each group was then randomly allocated to 1 of 3 dietary treatments: (1) A control (CON) diet in which cows were individually offered 14.0 kg of alfalfa hay DM/d and 4.3 kg of concentrate mix DM/d; (2) a DGM diet in which cows were individually offered 9.0 kg of alfalfa hay DM/d, 5.0 kg of DGM DM/d, and 4.3 kg of concentrate mix DM/d; or (3) an EGM diet in which cows were individually offered 9.0 kg of alfalfa hay DM/d, 5.0 kg of EGM DM/d, and 4.3 kg of concentrate mix DM/d. The EGM used in this experiment had been ensiled for 11 mo. The concentrate mix contained 93.0% crushed wheat, 4.7% dried molasses, and 2.3% mineral mix (DM basis). The CON treatment group had 12 cows assigned to it, whereas the DGM and EGM treatment groups each originally had 10 cows. However, 1 cow in the EGM treatment group contracted mastitis and was removed from the experiment. On d 1 to 16 of the experiment, all cows received the CON treatment so that covariate measures could be obtained. From d 17 to 19, cows allocated to the DGM and EGM treatments transitioned onto their dietary treatment, with the CON cows remaining
on their CON diet. All cows then were offered their full allocated treatment diet until d 37; that is, for 18 d duration.