EFFECTS OF SUPPLEMENTATION OF ENERGY OR RUMINALLY UNDEGRADED PROTEIN TO LACTATING COWS FED ALFALFA HAY OR SILAGE

Alfalfa was harvested as silage or hay and fed in two 12-wk trials wit h a 4 x 4 Latin square design that used 12 (trial 1) or 24 (trial 2) m ultiparous lactating cows (4 ruminally cannulated cows per trial). Die ts contained (dry matter basis) 75 or 50% alfalfa plus 24 or 40% high moisture corn (trial 1) or 50% alfalfa, 44 or 41% high moisture corn, with (3%) or without fish meal (trial 2). Experiments were conducted t o evaluate the responses of cows fed alfalfa hay or alfalfa silage die ts to an increase in protein supply from microbial protein synthesis ( trial 1) or from the supplementation of ruminally undegraded protein ( RUP) (trial 2). In trial 1, the increase in high moisture corn in the diet increased both milk protein and microbial crude protein yields (e stimated from the excretion of purine derivatives) to a greater extent for the cows fed the alfalfa silage diets (170 and 337 g/d, respectiv ely) than for the cows fed the alfalfa hay diets (100 and 100 g/d, res pectively). In trial 2, RUP supplementation (as fish meal) increased m ilk protein yield 100 g/d for cows fed alfalfa silage diets and 20 g/d for cows fed alfalfa hay diets. These results indicated that protein status was poorer and, thus, more responsive to absorbable protein fro m microbial protein (trial 1) or RUP (trial 2) for cows that consumed alfalfa conserved as silage versus those that consumed alfalfa conserv ed as hay.