Influence of brown midrib, leafy, and transgenic hybrids on corn forage production

Hybrid selection strongly influent es corn (Zea mays L.) forage production. Limited forage production and quality information exists for leafy and tra nsgenic hybrids [Bacillus thuringiensis (Bt) and herbicide resistant]. We c ompared dry matter (DM) yield, forage quality, and estimated milk yields of these and brown midrib hybrids with dual-purpose hybrids fur 3 yr at harve st densities of 66 000 and 84 000 plants ha(-1). Transgenic hybrids had no effect on DM and milk yields, so we do not recommend Bt hybrids under condi tions of low infestation of European corn borer (Ostrinia nubilalis Hubner) , Leafy hybrids had similar DM and milk yields as hybrids of similar maturi ty. Brown midrib hybrids, which had DM yields that were about 20% less than those of hybrids of similar maturity, had 40 to 80 g kg(-1) greater in vit ro true digestibility (IVTD) and 70 to 200 g kg(-1) greater neutral deterge nt fiber (NDF) digestibility. Brown midrib hybrids had the greatest or leas t milk yields among hybrids, depending on hybrid and year. Leafy and brown midrib hybrids mostly had low harvest index (HI) values. which had strong n egative correlations with NDF in all years (-0.71, -0.44, and -0.90). Brown midrib hybrids had high NDF digestibility, which had strong positive corre lations with IVTD (0.80, 0.88, and 0.86), Currently, we do not recommend br own midrib hybrids because of inconsistent milk yields and high seed costs. Development of brown midrib and leafy hybrids with greater HI values shoul d result in excellent forage hybrids.