By Åshild T. Randby
Senior researcher in the Department of Animal and Aquaculture Sciences, Agricultural University of Norway.

Organic farming in Norway, as in other countries, is subject to several restrictions. One of them is that, in the feed ration for ruminants, the proportion of concentrates should not exceed 40%. In Norway, silage of grasses or grass/clover mixtures are the major winter feed for all ruminants. The quality of this silage is increasingly important as the proportion of concentrates in the ration decreases.

In a series of 14 studies, growing young stock were provided with free access to silage of various quality standards, unsupplemented or supplemented by a low level of concentrates. Together with data from the literature, these led to the growth curves as illustrated in the Figure below.

Effect of Concentrate Supplementation and Silage Quality on Daily Weight Gain of Steers

The curves illustrate how the daily weight gain of NRF steers (Norwegian cattle breed) in beef production was influenced by silage quality when fed freely together with a series of fixed amounts of concentrate. Silage quality clearly makes the greatest difference with the lower rations of concentrate that are typical of organic farming. The general relationship between silage quality, the amount of concentrates and production response will be the same for dairy cow nutrition.

The major factors influencing the quality of silages used in these studies were maturity of the grass, the use of acidic silage additives and ensiling in bales. The literature indicated that a grass clover mix is preferable to a pure grass sward and that rapid wilting before ensiling and chopping prior to feeding was beneficial.

The quality of baled silage depends heavily on the competence of the people involved and the technology used. The crop should be mown at a young leafy stage, when it is easy to compact and its nutritional quality is high. Also a 10 – 30% content of clover increases intake by the cattle. The aim should be a short wilt in dry, windy weather to a minimum of 20% DM. Preferably it should be wilted to 25 – 35% DM.

Although higher DM levels may reduce the costs of baling and wrapping, as fewer bales are needed, highly wilted crops are difficult to compact and are susceptible to mould growth. A well compacted bale wrapped with sufficient layers of good quality plastic provides the best insurance against mould growth. It is important to protect the plastic from damage, which means wrapping at the point of storage is better than transporting bales from the field to the final place of storage.

The flexibility of bale silage offers further advantages. It can be made during short spells of dry weather, stopping easily when it rains, and silage of the required quality can be selected from the store at any time.

A high forage intake, important in organic farming, requires that the silage is neither poorly nor extensively fermented. Restrictedly fermented silage, giving the highest intake, may be obtained by wilting the crop to at least 30% DM, or by treatment with acidic additives. Trials in 2003 have indicated the effectiveness of a novel non-corrosive acidic additive, and approval for use in organic production may be granted during 2004.

References

Randby, Å.T. 2001. Beef from forage: The potential of high quality grass silage. Proc. from seminar no. 326, The Nordic Association of Agr. Scientists (NJF): Production and utilization of silage. Lillehammer 27-28.Sept.2001, 46-51.

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