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Many crops produce large amounts of residues that have to be disposed of, such as straw from cereals and legume pulses and stalks and stover from maize. These residues contain nutrients which can be used in ruminant feeding but, because of their low digestibilities, they are considered to be poor feeds. In many instances, the nutritive value of poor feeds can be improved by means of physical and chemical treatments and then employed as ingredients in complete diets. As an alternative, straws can be utilized as such, with no treatment, with good results provided they are properly associated with other feeds. The utilization of crop residues as animal feeds is of particular importance in the Mediterranean region, where good forages are often limited.
The treatment of barley straw with urea was studied in Spain (Instituto Nacional de Investigaciones Agrarias) in feeding trials with ewes and lambs. The most adequate level of urea resulted in a 5-6% increase in digestibility over the straw dry matter, and an adequate amount of water (30-40%) had to be added to achieve the highest level of digestibility. During storage in sealed containers, the best results in upgrading the straw's nutritive value was obtained with high temperatures (35 C).
The association of wheat straw with other feeds was investigated in Italy (Dipartimento di Scienze Zootecniche Firenze) and Portugal (Estação Zootécnica Nacional, Santarém) in feeding trials with lambs and in in vitro studies. The treatment with urea seemed not to be necessary: very good results could be achieved with untreated straw, when properly supplemented with slowly degradable protein feeds. Maize gluten feed was a better protein source than sunflower meal, but not as good as soy bean meal. All the tested protein feeds of animal origin (meat, fish, blood) were undoubtedly the best supplements, comparable with each other and with soy bean meal. If soy bean meal was integrated with the protected aminoacids, lysine and methionine, the beneficial effect of such an an integration was evident at low levels of crude protein in diet dry matter (13%), but disappeared at higher levels (18%).
Maize stover was studied in Spain in feeding trials with lambs. The treatment with urea (3.55%) and water (25-30%) was beneficial in upgrading the feed. Supplementation with barley meal was useful in improving the animals' performances, so confirming that the readily available nitrogenous source represented by retained ammonia, needs to be balanced by an equally quickly fermentable energy source.
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