PERFORMANCE OF LACTATING DAIRY-COWS FED EITHER ALFALFA SILAGE OR ALFALFA HAY AS THE SOLE FORAGE

Alfalfa was harvested from alternate windrows as 40% DM silage or hay in small rectangular bales and fed in two 12-wk 4 x 4 Latin square trials, each with 20 multiparous lactating cows (4 with ruminal cannulas). Diets contained (DM basis) 69 (trial 1) or 66% (trial 2) alfalfa, 26 to 33% high moisture corn, 1.3% minerals and vitamins, and about 1.6 Meal of NE(L)/kg of DM. In trial 1, second-cutting silage (21.2% CP) and hay (19.7% CP) containing 35% NDF were fed in diets: 1) silage (17.3% CP), 2) hay (16.3% CP), 3) silage with 3% fish meal (19.1% CP), and 4) hay with 3% fish meal (18.1% CP). Cows had lower DMI and lost BW on diet 1. Yields of milk and milk components were similar on diets 1 and 2 and greater on diet 3 than on the other three diets, except that fat yield was greater on diets 1 and 3 than on diets 2 and 4. In trial 2, first-cutting silage and hay containing 19.9 and 16.5% CP and 40 and 41% NDF were fed in diets: 1) silage (16.8% CP), 2) hay (14.6% CP), 3) silage with 3% fish meal (18.2% CP), and 4) hay with 3% fish meal (16.0% CP). Cows had lower DMI and lost BW on diets 1 and 3. Generally, yields of milk and milk components were lower on diet 1 than on diets 2, 3, and 4; only protein yield was greater on diet 4 than on diet 2. In both trials, fish meal increased mean protein yield 100 g/d on silage and 30 g/d on hay. Apparent digestibilities of DM, NDF, and ADF; concentrations of NH3 and total AA in the rumen; and urea in milk and blood were greater when cows were fed silage. The energy value of alfalfa silage exceeded that of hay, but absorbed protein was more limiting for alfalfa silage than for hay when fed to lactating cows as the sole forage.