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 Mcal of NEL/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.(ABSTRACT TRUNCATED AT 250 WORDS)