The objective of this study was to quantify the proteolytic activity of a set of 10 diploid early intermediate heading cultivars of Lolium perenne under rumenlike conditions. A field experiment was conducted in Northern Germany, where the perennial ryegrass cultivars were grown during two growing seasons. Leaves of the first and second cut were sampled in the field, sterilized with 800 ml. l−1 ethanol solution and incubated for 0, 6, and 24 h under rumenlike conditions (darkness, 39°C, pH 6.5) without the presence of rumen microbes. Results revealed that the leaf protein content declined with increasing incubation time, confirming the involvement of plant-mediated proteolysis in the degradation process. Gel electrophoresis illustrated that the decrease in protein content is probably mainly caused by the loss of the large subunit of Rubisco (ribulose-1, 5-bisphosphate carboxylase/oxygenase), which was entirely degraded during the incubation time. Although differences among harvests and years were evident, genetic variation among the 10 diploid perennial grass samples concerning protein degradation rates and degradation characteristics was not detected.
Plant maturity substantially influences the yield and quality performance of grasses. Grass phenology is often not considered objectively to evaluate the new genotypes prior to registration. Measuring the mean stage by count (MSC) is time consuming, and simplified approaches are, therefore, required. Twenty diploid, intermediate heading Lolium perenne L. genotypes were evaluated in a 2-year field study in Northern Germany for yield and the content of Neutral Detergent Fiber (NDF), Acid Detergent Fiber (ADF), Acid Detergent Lignin (ADL), and digestible organic matter (DOM). Data from the first and second cut, each comprising three sampling dates, were included in this study. A simplified maturity index (SMI8), expressing the percentage of tillers at or beyond the boot stage, from MSC was derived. This index resulted in similar correlations with yield and quality parameters compared to MSC but is easier to use and less laborious. The SMI8 reduced the variations among genotypes, as for the first cut NDF and ADF content, where the genotype effect disappeared after considering SMI8 as the covariable. Moreover, the ranking of the genotypes was slightly modified for most studied traits, indicating that a large part of the variations in the studied parameters was caused by variations in maturity.
Two in vitro methods were tested to establish their potential to predict the metabolizable energy (ME) content of forage legumes: the Tilley and Terry (TT) method and the pepsin-cellulase method (CM). Different samples of white clover (Trifolium repens L.), red clover (Trifolium pratense L.), kura clover (Trifolium ambiguum M. Bieb.), lucerne (Medicago sativa L.), and birdsfoot trefoil (Lotus corniculatus L.) were derived from field trials with several defoliation systems at two sites. The CM was more precise due to its repeatability within and between analysis runs, but eventually overestimated the ME contents of the samples, as it was shown for the standard samples with known in vivo digestibility. ME contents were found to be consistently higher based on CM, with a difference of up to 1.5 MJ ME/kg DM compared to TT. Although white clover was, in general, the species with the highest ME content, the influence of legume species over all cuts and defoliation systems was inconsistent. Such observations may influence the method of choice for ME estimation for large datasets.