In vitro degradation kinetics of protein and carbohydrate fractions of selected tropical forages

Abstract

Whereas obtain detailed information about nutrient composition and degradation rates of carbohydrate and protein fractions of tropical forages is essential to determine how much of each nutrient can be used by the animal and the main limiting causes to the level of production. A descriptive study was conducted to evaluate the degradation rate of protein and carbohydrate fractions and understand degradation synchronism of carbohydrates and protein fraction in the rumen of goats fed Tifton 85, mulberry and leucaena forages. Contents of crude protein (CP), non-protein nitrogen (NPN), neutral detergent insoluble nitrogen (NDIN) and acid detergent insoluble nitrogen (ADIN) were measured to obtain the protein fractions A, B1, B2 and C. Degradation profiles of nitrogen fractions were obtained in vitro incubating the forages samples with proteases from Streptomyces griseus. Contents of sugars, starch and soluble fiber (neutral detergent NDSF) were analyzed to determine the fractions A and B1 from total carbohydrates (TC), whereas for fraction B2, C and degradation rate of fraction B2, the gravimetric technique of in vitro degradation of the fiber was used through kinetic interpretation of degradation profiles. It was adopted descriptive statistics to summarize the dataset, to describe the data, tables were compiled and used sample average as position measurement. Regarding Tifton 85, the sum of fractions A and B1 was 51.61 g/100g CP and the fraction B2 was 38.74 g/100g CP. Thus, the portion of slowly degradable protein from this forage is higher and tends to escape from rumen contributing with amino acids in the small intestine. Differently, most of the protein from mulberry and leucaena are present as highly degradable protein in rumen (B1), requiring supplementation with readily fermentable carbohydrate for a better utilization of nitrogen compounds. Considering the partitions of protein in different compartments of the plant, possibly the mixture between forages promotes a better balance for the use of this nutrient by animals. Fractions representing about 80g/100g of the protein from Tifton 85 presents problems to be used by animals. This means that, despite the high levels of protein in Tifton 85, metabolizable protein deficit may occur at any time after the intake of forages by the animals. Mulberry and leucaena are extremely degradable feed, both for cellular content and cell wall, with high possibility of presenting good synchronization between degradation of carbohydrate and protein.