Variability in methanogenic potential of the pasture legume Biserrula pelecinus

Summary

​A cultivar of Biserrula pelecinus (biserrula) has been demonstrated to have a ten-fold lower methanogenic potential in the rumen than lucerne (Medicago sativa) when grown in the glasshouse and tested in batch culture in vitro. However, it also reduced the overall microbial fermentation.  A core collection of biserrula accessions has recently been established and the main aim of this study was to investigate this core collection for candidates that may have low methanogenic potential without affecting ruminal fermentation more generally.  

The initial observations of antimethanogenic bioactivity in biserrula were based on plants grown in a glasshouse, under controlled conditions. The second aim of this project was to investigate the antimethanogenic potential of biserrula in more detail by screening samples of biserrula grown in-field under different environmental conditions, and at various stages of growth in vitro, to determine the degree of variation in its methanogenic potential. We also examined the level of inclusion of biserrula needed within a mixed substrate to reduce methane without reducing overall fermentation as well as the persistency of the effects. All samples taken during this experiment were screened using an in vitro batch culture system based on rumen fluid collected from sheep.  The parameters that were measured as indicators of the bioactive effects of biserrula were: methane, total gas, VFA and ammonia production and the acetate to propionate ratio.  

The most bioactive accession was also examined at different levels of inclusion in a mixed substrate for fermentation in batch culture and then extended to a continuous RUSITEC culture systems to better mimic the ruminal environment and test the persistency of the bioactive effects. The most bioactive accession was also used to examine crude extracts of biserrula using different solvents to help identify the fractions that contained the bioactivity. There was significant variation in methanogenic potential amongst the cultivars within the core collection, but they all reduced both methane and overall microbial fermentation. However, biserrula reduced methane production when it was used as part of a mixed diet and affected methane and most of the fermentation parameters in a favourable way when it was included as 50% of the diet.  We have preliminary evidence that these results occur in continuous culture and persist for over a week. There was a definite effect of eco-geographical factors and the age of plant on bioactivity and testing the plant extracts suggested that there is more than one compound responsible for the bioactivity we observed in the plant.

Our results were used to determine which cultivars should be evaluated in vivo and identify how these cultivars are to be integrated into farming systems of the future.  ​