LIVESTOCK FEEDING
Silage Wars
By Greg Stewart, OMAFRA Corn Specialist

Corn silage production has traditionally been an essential part of dairy and beef operations. In fact, the relative importance of corn silage continues to increase in Ontario. It offers consistent quality, high dry matter and energy yields per acre. It allows for rapid filling of horizontal silos, provides increased opportunities for nutrient management, and corn hybrids have been improving.

Until recently, it was generally thought that any improvement in hybrids for silage purposes occurred only as a by-product of improving grain hybrids. In fact, research in the 1980s at the University of Guelph evaluated corn hybrids for silage yield and quality and concluded that the two main factors to consider in hybrid selection were relative maturity (select a hybrid to ensure 35 per cent dry matter before frost) and grain yield (the best grain hybrids are generally the best silage hybrids).

In the last five years however, there has been considerably more interest in silage quality and in breeding corn hybrids specifically designed for silage use. The promotion of single-purpose silage hybrids has challenged the belief that a good grain hybrid is automatically a good silage hybrid. These silage-specific hybrids, for the most part, have been based on incorporating certain traits into the plant make-up.

Two of the better known traits which are available in silage hybrids grown in Ontario are:

1. the leafy characteristic (plants have several extra leaves above the ear, relatively lower ear placement and are generally taller than grain hybrids)
2. brown mid-rib trait (plants have a brown mid-rib in leaves and lower lignin content in the cell walls)

Some seed corn companies have elected to breed silage specific hybrids, in many cases by including a novel trait in the hybrid. Others continue to breed more along the lines of dual-purpose hybrids. Nearly all companies, however, are doing considerably more evaluation of silage characteristics, building a list of quality traits and promoting certain aspects as the key to improved silage quantity, silage quality and animal performance.

Yield of Grain and Stover
Total forage yield is one of the key factors in selecting a silage hybrid. Harvest index (ratio of grain to whole plant) has traditionally been fairly constant among corn hybrids, so selecting hybrids with high grain yields generally corresponded to high forage yields. New silage specific hybrids – with taller, leafier plant structures – claim to be capable of higher total silage yields than dual-purpose hybrids. Is this accomplished by increasing stover yield at the expense of grain and energy levels? Research conducted at Agriculture and Agri-Food Canada in Ottawa evaluated the growth and composition of several leafy hybrids compared to several dual purpose hybrids. The indications from this research were that the leafy hybrids could maintain grain-to-stover ratios not far behind those of dual-purpose hybrids (see Table 1).

The proponents of silage-specific hybrids claim there is little correlation between grain levels and silage quality. The counter claim to this argument is that because grain is much higher in energy than stover, you simply cannot maximize silage quality and energy levels if grain yield is sacrificed. In any case, producers need to select hybrids which have relatively high total silage yields, since selecting a hybrid with marginal yield potential places an increasing burden on some other feature of the silage (i.e., grain quantity, digestibility, etc.) to make up the difference. If forage or effective fibre is generally in short supply in your farming operation, then total yield may rank higher than any other selection characteristic.

Digestibility
Digestibility ratings of corn hybrids intended for silage are becoming increasingly important and available. Research has shown there is enough range in digestibility among hybrids to warrant accurate digestibility evaluations and use of these evaluations in hybrid selection. Inevitably, digestibility scores need to be combined with yield to arrive at total digestible yields. Selecting a hybrid based predominantly on high digestibility may be flawed if other considerations are not included. Research involving several corn hybrids in New York state indicated that the value of high digestibility associated with the brown mid-rib hybrid needs to be weighed against lower yields (see Table 2). However, if forage or effective fibre supplies are plentiful, high digestibility or energy value ratings may be the most important silage characteristic for your farm.

Producers are sometimes led to believe digestibility and/or yield may increase in higher density stands. Research out of Cornell University advised silage growers who had been adopting narrow row and ultra high populations (45,000 - 50,000 seeds/acre) that there were no advantages for any of the hybrids tested to having stands of more than 35,000 plants/acre in either narrow (15 in.) or wide (30 in.) rows. In fact, this study showed a steady decline in silage digestibility across all hybrids as populations increased from 18,000 to 42,000 plants/acre. Other studies have generally confirmed that final plant stands of 26,000 to 30,000 plants/acre optimize yield and quality. There is little likelihood of a hybrid being particularly adapted to very high populations.

Hard, high density kernels and fast dry down are desirable traits for grain hybrids. But these characteristics are generally undesirable in corn silage. Ideally, silage specific hybrids should have kernels that are soft in texture, to increase starch digestion in the animal. Slow rates of dry down widen the silage harvest window and reduce the risk of being forced to ensile overly hard kernels and/ or overly dry silage. Silage processing has been shown to increase silage quality, especially on hybrids that have naturally hard kernels or when conditions have forced harvesting past the optimum moisture content. Planting several hybrids of varying heat unit ratings can also build more flexibility into the harvesting schedule.

Finally
If you’re tired of arguing over red tractors versus green tractors, the debate over silage hybrids should provide you with some increased stimulation. When selecting silage hybrids try to make decisions based on as much evidence as possible. Note that the two tables in this article showed the same two hybrids with different yield rankings. Be careful to compare hybrids of similar maturities; it is not fair to compare hybrid A which reaches one-half milk line at 2700 heat units to hybrid B which may already be at black layer. If you have consistently grown a dual purpose hybrid for both grain and silage be aware of the ongoing efforts to tailor corn plants to enhance silage traits and animal performance. If you already select silage-specific hybrids, realize that the hybrid lifespan will continue to shorten and the need for constant comparisons and change is great.

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