Organic matter and crude protein digestibility predicted from nitrogen and fibre fractionation of festulolium hybrids

Abstract

The objectives of the experiment were to study nitrogen fractions of the Cornell Net Carbohydrate and Protein System (CNCPS) and digestibility of organic matter (OMD) and crude protein (CPD) along with the possibilities for predicting OMD and CPD based on chemical composition and CNCPS nitrogen fractions. Thirty samples of festulolium hybrids (fescue hybrids and ryegrass hybrids) commonly used and certified in the Czech Republic were analyzed for chemical composition, brutto energy, and nitrogen fractions, these fractions being A (non-protein nitrogen), B1 (rapidly degradable protein), B2 (intermediately degradable protein), B3 (slowly degradable protein), and C (unavailable protein). OMD and CPD were determined by near-infrared reflectance spectroscopy. Nitrogen fractions showed similar mean values for both analyzed groups of festulolium hybrids. Mean rapidly, intermediately, and slowly soluble fractions (B1, B2, and B3, respectively) were 29.2, 30.7, and 33.7 g/kg of dry matter (DM) for fescue hybrids and 21.7, 33.5, and 31.9 g/kg of DM for ryegrass hybrids. There was a trend for fraction B2 to decrease with advancing maturity in relation to neutral detergent insoluble protein value. The mean content of bound fraction C was 10.4 g/kg of DM for fescue hybrids and 7.3 g/kg of DM for ryegrass hybrids. Three groups of hybrids were evaluated statistically: fescue (I), ryegrass (II), and combined fescue/ryegrass (III). Better regression equations were found for fescue/ryegrass hybrids. High degrees of CPD determination were identified with predictors of individual nitrogen fractions (R² = 0.975; P > 0.0001). OMD was described in regressions only using nitrogen fractions A and B1 (R² = 0.500; P > 0.0001).