Forage evaluation, chemical composition, and in vitro digestibility of continuously grazed star grass

Abstract

This study evaluated the chemical composition and dry matter (DM) digestibility of leaf, stem, and senescent fractions of star grass (Cynodon plectostachyus Pilger) in summer and winter in the south of Brazil. Four 17.6 ha pastures grazed by growing steers in continuous grazing were used. The experiment was divided into two periods: (I) summer: February to June, when five cuts were made; (II) winter: June to October, with six cuts. The forage samples were collected at nine pasture points every 28 days. The DM availability reduced linearly in the summer. In the winter, after September there was a recovery of DM availability. In the summer, there was a linear reduction in leaf proportion and a linear increase in senescent fraction. In the winter, there was a reduction in stem proportion and the senescent fraction increased. Leaf proportion had a quadratic response. The mean crude protein (CP) levels, neutral detergent fiber (NDF), and acid detergent fiber (ADF) during the summer in the leaves were 11.8, 68.6 and 36.1%. The levels were 5.5, 79.3 and 48.8% for stems and the levels were 3.6, 83.0 and 50.2% for the senescent fraction. During the winter, the average levels of CP, NDF and ADF in the leaves were 12.9, 62.2 and 32.7%. The levels were 4.7, 81.2 and 50.1% for stems and 4.1, 84.6 and 54.0% for the senescent fraction. The percentage of indigestible CP in relation to CP was 20% for leaves, 74% for the senescent fraction, and there was variation with time for the stems with levels between 20 and 90%. The DM digestibility of the forage during the summer had a linear reduction and a quadratic behavior during the winter with an average level of 54% in the summer and 42% in the winter.