Gijs Van Ranst

Variability of the Rumen Escape Protein and Fatty Acid Composition of Grass and Clover Species and Cultivars

Increase of rumen escape protein (REP) and higher content of poly-unsaturated fatty acids (PUFA) in forage are getting risen interest. In this work, fast, reliable and cheap methods were developed to predict REP and C18:3 content using dried, ground and stored samples of grasses and clovers. Prediction of REP was possible using a regression curve and robust NIRS calibrations for in vitro digestibility and ADF, as well as the determination of moisture. Evaluation of C18:3 content was also possible by NIRS. Samples from plots (3 replicates, 5 cuts, 2 N fertilizer levels) of perennial and Italian ryegrass, timothy, orchard grass, meadow fescue, tall fescue, red clover and white clover were analysed using these methods. Variation for REP and C18:3 content was present between and within most species. Orchard grass presented the highest average REP while perennial ryegrass had the lowest one. For C18:3, timothy showed on average the highest content while Italian ryegrass had the lowest one. There were no significant differences in C18:3 content and REP within the fescue species. The white clover presented significantly lower REP and higher C18:3 content than the red clover. The red clover presented no significant differences within species for REP. In general, more variation for REP was present in the grasses while the clovers presented more variation for C18:3 content.

Influence of Forage Species, Cultivar and Cut on Lipid Metabolism During the Ensiling Process

Lipid metabolism in silage, mainly lipolysis, of different species (perennial ryegrass, red clover and white clover) and three cultivars of white and red clover at three cutting dates in one growing season (April, July and October) were studied. Lipolysis in silage was influenced by cutting date, species and to some extent by cultivar. Furthermore, in some cuts silages of red and white clover displayed a lower lipolysis than silage of perennial ryegrass. On average, over the three cutting dates, respectively 90.3%, 86.4% and 85.7% of the membrane lipids in perennial ryegrass, red clover and white clover were hydrolysed during ensiling. In red clover this could be due to the lipid-protecting properties of polyphenol oxidase (PPO) activity. This was not observed in perennial ryegrass or white clover. Nevertheless, differences in lipolysis in silage between cultivars of red clover were not correlated with PPO activity.