Effect of a harvest time and cultivar on the chemical composition and in vitro ruminal dry matter degradability of perennial ryegrass (Lolium perenne L.)

The aim of this study was to determine the effect of a harvest time on the chemical composition and dry matter degradability of perennial ryegrass (Lolium perenne L.) depending on a swath and cultivar (Bajka - diploid; Baronka - tetraploid). The herbage was harvested at four times of the day (6:00, 10:00, 14:00, 18:00) – the first swath on 15th May 2012, and next after 4, 5 and 6 weeks. Chemical composition and dry matter degradability after 48 hours of in vitro incubation were determined. All the analyzed treatments had an impact on the content of DM, crude protein and soluble and structural fractions of carbohydrates. The diploid cultivar had a greater content of DM, WSC and aNDF (P<0.01) and a lesser content of crude protein and ADF (P<0.01) compared with the tetraploid cultivar. Dry matter of the first swath herbage was characterized by the greatest content of WSC and the least content of aNDF (P<0.01). In each consecutive swath, the WSC content significantly decreased (P<0.01) while aNDF increased (P<0.01). The increase in DM content between 14:00 and 18:00 was due to the deposition of products of photosynthesis, which is confirmed by a parallel increase in the concentration of WSC. The effect of treatments on the degradability of DM in vitro has not been confirmed, but the results indicate a smaller impact of a cultivar than the harvest management. Numerous interactions between the analyzed treatments indicate the need to choose the harvest time depending on a genotype and swath. Ruminal degradability indicates that high value ryegrass can be obtained regardless of the harvest time during the day. However, greater suitability for ensiling was shown by the diploid cultivar harvested at 10:00 and the tetraploid harvested at 18:00.