Diurnal variations on pasture chemical composition and fermentability

Abstract

The aim of this work was to study diurnal variations in chemical composition and ruminal fermentability of a wide range of forages (A. sativa, L. multiflorum, L. perenne, L. hybrid, B. auleticus, M. sativa, T. pratense, T. repens, T. alexandrinum, L. corniculatus, L. pedunculatus, L. tenuis, C. intybus, P. dilatatum, P. notatum, P. plicatulum, P. lanceolata, S. sudanense). Thirty paddocks involving different species at vegetative stage were sampled at 09:00, 13:00, and 17:00 h on the same day (treatments). Samples were subjected to chemical analysis and an in vitro gas production trial. Gas volumes were fitted to a dual-pool logistic model with single lag. A mixed model was used for statistical analysis, considering time of cut as fixed effect, and botanical group and season as random effects. The concentration of water-soluble carbohydrates (WSC) and the ratio WSC/N increased along the day, while neutral detergent fibre (NDF) and N contents decreased. This led to a shortening of lag time from the morning to the afternoon. Fibre content was associated with a longer lag time, a higher slow volume and lower fermentation rates. Pastures cut in the afternoon showed earlier onset of ruminal fermentation associated with lower concentrations of fibre and higher concentrations of soluble carbohydrates.