Two studies were conducted to evaluate the effect of a glyphosate-tolerant (event nk603) and a corn rootworm protected (event MON863) corn hybrid on feed intake and milk production compared with the nontransgenic hybrid and two reference hybrids. In Experiment 1, 16 multiparous Holstein cows were assigned to one of four treatments in replicated 4 x 4 Latin squares with 28-d periods. Diets contained 40% (dry matter [DM] basis) of either 1) glyphosate-tolerant corn silage (GT), 2) nontransgenic control corn silage, or 3) two nontransgenic reference hybrids which are commercially available. Each diet also contained 23% corn grain from the same hybrid that supplied the silage. At ensiling, rapid drying conditions prevailed and the GT hybrid was the last to be harvested which resulted in greater DM content at similar physiological maturity. The 4% fat-corrected milk (FCM) yield and DMI were reduced for cows fed the GT corn diet due to the higher DM content of the GT silage (37.1 vs. 33.2 kg/d and 4.05 vs. 3.61% of BW, respectively). There was no effect of the GT diet on milk composition or efficiency of 4% FCM production that averaged 1.43 kg/kg of DM intake for all diets. In Experiment 2, 16 multiparous Holstein cows were assigned to one of four treatments in replicated 4 x 4 Latin squares with 21-d periods. Diets contained 26.7% (DM basis) corn grain from either 1) corn rootworm protected (event MON863) corn hybrid, 2) nontransgenic control corn hybrid, or 3) the same two nongenetically enhanced reference hybrids used in Experiment 1. The 4% FCM yield (34.8 kg/d) and DM intake (4.06% of BW) were unaffected by diet. Efficiency of FCM production (average 1.32 kg/kg of DMI) was not affected by diet. In summary, these two studies indicated that insertion of a gene for glyphosate tolerance or corn rootworm protection into a corn hybrid did not affect its nutritional value (as measured by efficiency of milk production) for lactating dairy cows compared with conventional corn hybrids.