From 2009 to 2012 in our planting date studies we compared silage yield and quality of full-season grain and brown midrib hybrids at five planting dates in each year.
The forage yield of a full-season grain hybrid was always higher than the forage yield of a brown midrib hybrid (Figure 1). However, the NDFD content of a brown midrib hybrid was always higher than the NDFD content of a grain hybrid. Starch content of both types of hybrids was similar when planted early, however, the starch content of brown midrib hybrids was lower with later planting dates.
Figure 1. Corn forage yield, ivNDFD and starch content response of full-season grain and brown midrib hybrids (104-108 d RM) to planting date during 2009 to 2012 at Arlington, WI (N= 160 plots).
During these years Milk per Ton was not affected by planting date for full-season hybrids (Figure 2 in http://wisccorn.blogspot.com/2013/05/B037.html), Milk per Ton decreased with later planting date. For brown midrib hybrids, Milk per Ton was best when planted early, but decreased as planting was delayed. The full-season grain hybrid always produced more Milk per Acre than the full-season brown midrib hybrid even though the energy in the NDFD pool was always greater. The difference is made up by the energy in the starch pool of a grain hybrid.
Figure 2. Corn forage milk per ton and milk per acre response of full-season grain and brown midrib hybrids (104-108 d RM) to planting date during 2009 to 2012 at Arlington, WI (N= 160plots).
The details of these studies can be found at http://corn.agronomy.wisc.edu/Research/Default.aspx.