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Twenty lactating Holstein cows were used to determine the nutritional value of eastern gamagrass. Dietary treatments consisted of 1) gamagrass hay and no corn (HNC), 2) gamagrass silage (S) and no corn (SNC), 3) S and low corn (SLC), 4) S and medium corn (SMC), and 5) S and high corn (SHC). Gamagrass fed as hay or silage did not change (P>0.10) milk yield, but corn inclusion tended to increase (P<0.08) milk yield. Yields of milk protein (0.69 vs 0.80 kg/d), lactose (1.23 vs 1.44 kg/d), and solids-not-fat (2.12 vs 2.48 kg/d) tended to be greater for SNC than for HNC (P<0.08). Corn inclusion increased milk yields compared with SNC. Gamagrass fed as silage resulted in a greater feed conversion efficiency than did gamagrass fed as hay (2.16 vs 1.88; P<0.01). Adding corn to S reduced feed efficiency. Conversion of feed N to milk N was greater (P<0.01) for gamagrass fed as silage than for hay. Milk urea N (MUN) concentration was greater (P<0.01) for cows fed HNC than for cows on all other treatments. Feeding S significantly lessened MUN concentration. Including corn at the medium and high levels further reduced MUN concentration (P<0.05). Increased energy from corn at the high level increased milk yield and tended to increase conversion of feed N into milk protein. Gamagrass fed as silage without or with corn improved the N status of the cows, as indicated by lesser MUN concentrations.
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