Nutritive value of Trifolium pratense L. for ruminants estimated from in situ ruminal degradation of neutral detergent fibre and in vivo digestibility of organic matter and energy

Seven clover (Trifolium pratense L.) samples were collected at three different stages of the same sward (first growth (I), n = 3; first regrowth (II), n = 3; second regrowth (III), n = 1) during the growing season from 10th of May to 17th of August. Samples were analyzed for chemical composition, gross energy (GE) content, in vivo organic matter digestibility (OMD) and gross energy digestibility (GED) in sheep, and in situ rumen degradability of neutral detergent fibre (NDF). The contents of ash, crude protein (CP), crude fibre (CF), NDF, acid detergent fibre (ADF), acid detergent lignin (ADL) and GE were significantly (P < 0.05) affected by the time of cutting. Average values of 119.2, 197.7, 214.1, 400.7, 296.2, 73.8 g/kg of dry matter (DM) and 18.2 MJ/kg of DM were obtained for ash, CP, CF, NDF, ADF, ADL and GE, respectively. In general, OMD and GED decreased as the cutting time progressed, with average values of 72.4% and 70.2%, respectively. Effective ruminal degradability (ED) of NDF generally decreased (P < 0.05) with the increasing date of cutting at each stage, with the values 66.1% (May 10), 63.6% (May 18), 59.2% (May 25), 64.8% (June 29), 57.4% (July 7), 56.9% (July 13) and 51.6% (August 17). In situ measurements were characterised by an average value of 77.1% for the fraction of NDF potentially degradable in the rumen (b), 0.0703 h-1 for the rate constant of disappearance of fraction b (c), and 77.7% for digestible NDF (DNDF).