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Preservation of Home-Grown Cereals: Crimping or Urea-Treating?
An article by Dr Horst Auerbach, International Silage Consultancy (ISC), Wettin-Löbejün, Germany.
UK livestock farmers must either dry or in some way preserve their home-grown cereals for safe storage without spoilage because the cereals are usually too moist at harvest to leave untreated. Whilst a growing number of European farmers are now crimping (using an effective preservative, mostly based on organic acids and their salts, on all grains), treatment with urea, or urea-based products, has become popular in the British Isles. This article focuses on the major differences between the two preservation methods with the aim of helping farmers make the right decision.
Crimping using an acid-based or preservative salts-based product offers much more flexibility at harvest because of the wider moisture level parameters at which the grain can be harvested (Matthiesen et al., 2007). The maximum moisture content for urea use is about 22%. At higher moisture levels a fermentation process can take place which impairs, or stops completely, the release of the antifungal ammonia from the urea. This is due to the inactivation of the required enzyme, urease, when the pH drops below around 5.
Cereals for crimping are harvested at least three weeks earlier than for conventional harvesting and have been shown to have better hygienic quality, with much lower mould and mycotoxin levels than conventionally harvested grain (graph 1, Matthäus et al., 2004). This strategy does not affect the starch content as the starch filling process is already completed by that time, and the digestibility is usually higher. Furthermore, an earlier harvest creates more time for following cropping actions such as reseeding or catch-crops.
Interestingly, the organic acids used in crimping preservatives are fully metabolised by the animal, thereby increasing the energy content, depending on the acid used. For example, propionic acid (a major ingredient of crimping additives) has an energy content of ME 14.6 MJ/kg DM for dairy cows and ME 18.2 MJ/kg DM for fattening cattle. Finally, acid-treated cereals can be fed to all livestock categories, including non-ruminating young animals, without any restrictions.
There is no doubt about the antifungal effect of urea in non-fermenting cereals, but the frequently claimed positive effects on feed quality and animal performance need to be scrutinised. Indeed, urea increases crude protein content, but about 25% of the added substance will be lost by volatilisation and evaporation of ammonia during storage (Spiekers et al., 2005) and it only delivers readily available soluble nitrogen. This can be used by rumen micro-organisms for microbial protein synthesis, but it requires the simultaneous provision of sufficient quantities of immediately available carbohydrates in the ration. If ammonia and carbohydrate supplies are not in balance, surplus ammonia is quickly absorbed from the rumen and has to be detoxified in the liver. In grass- or grass silage-based feeding systems, soluble nitrogen is plentiful but rumen-undegradable protein (RUP) is limited, and RUP cannot be provided by urea supplementation. In turn, urea-treatedcereals are not helpful in meeting the dietary demand for RUP of, for instance, high-performing cows.
It should also be noted that, with the implementation of the EU Directive 1831/2003 on the use of feed additives in animal nutrition, urea has become a feed additive (category 3 –nutritional additives) and maximum concentrations in the diets apply. Before that time, it was simply a feed material to be used by farmers without any legal obligations. Today, farmers who want to use urea need a registration according to the EU Feed Hygiene Regulation 183/2005 and they must fulfil certain requirements regarding documentation, eg application rate in the diet and accuracy of mixing. Needless to say, only feed-grade urea is permitted for use in animal nutrition. When urea is added to cereals, the compound (ammonia) is automatically forced into all diets containing them. This will ultimately decrease flexibility in feed management.
In summary, both preservation methods can be used to make moist grain safe for storage until feeding. However, if one weighs the pros against cons, crimping using an effective preservative and good ensiling practice, offers maximum flexibility regarding harvest date and cereal inclusion in feed rations for all animal categories. In the quite unlikely situation of a lack of soluble nitrogen in the diet, urea can be added to grain or protein mixes or TMRs just prior to feeding.
List of references upon request.