Protein and carbohydrate fractionation of silages made from maize, Urochloa species and their mixtures

New feed assessment systems and methodologies for ruminants are being used with the aim of maximizing the use of nutrients by animals. The Cornell Net Carbohydrate and Protein System (CNCPS) considers the dynamics of ruminal fermentation and the potential loss of nitrogen in feed evaluation. We used this system to evaluate the protein and carbohydrate fractionation of silages made from maize and Urochloa species alone and in combination (70:30). The experiment was carried out under a completely randomized experimental design with 4 replications. Treatments comprised silages made from the following forages: maize (Zea mays); Congo grass (Urochloa ruziziensis); Xaraes palisadegrass (U. brizantha 'Xaraés'); Paiaguas palisadegrass (U. brizantha 'BRS Paiaguás'); 70% maize + 30% Congo grass; 70% maize + 30% Xaraes palisadegrass; and 70% maize + 30% Paiaguas palisadegrass. The results showed that despite the Urochloa exclusive silages having higher crude protein concentration than maize and mixed silages, they have a higher proportion of unavailable fractions with slow degradation rates, which can compromise animal performance. The maize silage and mixed silages had higher percentages of protein and carbohydrates with high degradation potential than Urochloa exclusive silages. Therefore, mixed silages represent one more alternative to provide forage with good nutritional value for ruminant feeding in times of feed shortage. Mixing grass and maize at ensiling would increase the volume of silage produced relative to ensiling maize alone without any significant reduction in quality of the silage produced. However, further studies are needed to determine the appropriate combinations of maize and grass at ensiling to produce silage with the desired nutritional value for the particular application and class of animals being fed. Feeding studies with animals would verify production levels achieved with the various silages.