The objective of this study was to assess in situ dry matter (DM) and neutral detergent fiber (NDF) degradation kinetics for two new pre-matured brown midrib varieties (pmBMR1 and pmBMR2) that can be double-cropped by harvesting at tassel, compared with a sole crop mature BMR (mBMR) and conventional corn silage (CCS) harvested at maturity in dry and lactating dairy cows. Potentially degradable DM fraction for the BMR hybrids were greater (P<0.01) than the CCS in both dry and lactating cows and was greatest for the mBMR in dry cows, while in lactating cows potentially degradable DM was greatest for the pmBMR1. Potentially degradable NDF fraction was greater (P<0.01) for BMR hybrids compared with CCS with the exception of the pmBMR2, which had the lowest potentially degradable NDF fraction in dry cows. Estimates of ruminal degradability of NDF were greater (P<0.01) for the pmBMR varieties compared to mature silages, and were greatest (P<0.01) for the pmBMR1 in both dry and lactating cows. Taken as a whole, this experiment indicates that rumen degradability may have been influenced more by hybrid than stage of maturity, as the pmBMR1 had the greatest degradability, and the pmBMR2 was not as degradable as the mBMR.