Fifty-six autumn-calving Holstein-Friesian cows, blocked on the basis of days in milk ( 27.6 +/- 10.65 d), lactation number ( 3.1 +/- 2.21), and preexperimental milk yield ( 28.4 +/- 6.69 kg) were used to examine the effects of replacing 330 g/kg of dry matter ( DM) of first-cut perennial ryegrass silage with either fermented whole-crop wheat ( WCW), urea-treated processed WCW, or corn silage on subsequent feed intake, milk production, and efficiency of nitrogen utilization. The DM ( g/kg), crude protein ( CP, g/kg of DM) and in vitro DM digestibility ( g/kg) of the forages were 204, 179, and 762 for grass silage; 389, 90, and 711 for fermented WCW; 795, 141, and 768 for urea-treated processed WCW; and 346, 93, and 783 for corn silage, respectively. Four forage treatments were evaluated as follows: 1) grass silage as the sole forage ( GS); 2) a mixture of grass silage and fermented WCW silage, ( F-WCW); 3) a mixture of grass silage and urea-treated processed WCW, ( UP-WCW); and 4) a mixture of grass silage and corn silage ( CS). In all cases, the alternative forages comprised 67% of the forage mix on a DM basis. Isonitrogenous diets were formulated by offering all cows 8 kg of concentrate as fed, formulated to different CP concentrations. Cows were offered these diets from 28 to 104 d in milk. Total DM intake and milk yield were greater on UP-WCW ( 20.0 and 30.2 kg/d) and CS ( 18.3 and 33.2 kg/d) than on GS ( 13.5 and 26.5 kg/d). Although DM intake was greater on F- WCW ( 17.1 kg/d) than on GS, milk yield was not significantly greater (+ 2.7 kg/d). Milk protein concentration was greater on F- WCW ( 30.5 g/kg), UP- WCW ( 31.3 g/kg), and CS ( 30.7 g/kg) than on GS ( 28.5 g/kg). However, there was no difference between treatments in milk fat or lactose concentrations. Body weight change was greater for cows offered GS (- 0.27 kg/d) than for those offered UP-WCW(0.01 kg/d) and CS (+ 0.05 kg/d) but not compared with those offered F- WCW (- 0.06 kg/d). There was no effect of treatment on plasma glucose, nonesterified fatty acids, beta-hydroxybutyrate, urea, or total protein at d 64 +/- 17.4 and d 92 +/- 17.4 postpartum. Efficiency of N utilization was greatest for CS with 0.36 of N intake being recovered in milk compared with 0.28, 0.32, and 0.26 for GS, F- WCW, and UP- WCW, respectively. There was no effect of treatment on milk urea N concentration or the urinary allantoin N to creatinine N ratio. The results of this experiment indicate that corn silage is a more suitable supplementary forage to grass silage than fermented or urea-treated processed WCW, with advantages realized in milk production and more efficient N utilization.
