So for the final blog of this month, I will be looking at
the potential of legumes to aid with livestock production from pasture based
systems. There is a well-known debate that
rears its head in the media from time to time about meat consumption and
methane emissions and how we should all be reducing our meat consumption to
reduce the effects of climate change and reduce emissions.
Running alongside this debate is a growing interest in the emissions
from pasture based systems. At the
moment, science has not advanced sufficiently to allow us humans to eat grass,
and digest the fibrous lignocellulose which ruminants are able to convert into
meat or milk and as such grazing livestock will continue to be part of our
environment. However where we can have
an impact is on how we manage that grassland to get optimal production from
that pasture. Making sure that there is
a balance of inputs and outputs to that grassland, ensuring adequate soil structure,
as well as optimising nutrient and animal management will allow us to use that
pasture to ensure efficient production.
One of the ways that grassland production can be “improved”
is to include legume species within the sward.
Grassland production will need to keep pace with requirements for higher
meat and milk production from ruminant systems and with a changing climate. Legumes offer important opportunities for sustainable
grassland based animal production because they can contribute to important key
- Increasing forage yield
- Substituting bagged N fertiliser inputs with
plants which are able to biologically fix nitrogen
- Mitigating and supporting adaptation to climate
- Increasing the nutritive value of herbage and
raising the efficiency of conversion of herbage to animal production
This blog content comes from a paper entitled “Potential of
legume based grassland – livestock systems in Europe” which was compiled by
Luscher et al and brings together information from a wide range of European research
on different properties of legumes to assess the contribution that legumes can make
to sustainable livestock production from grass.
To read the paper in full please click here.
For this blog in this monthly theme of livestock diets, the
bit that I will be concentrating on is the properties that are found in some
legumes that suppress methane production from ruminants. Without diving into a complicated
biochemistry and nutrition lecture, a key feature of legumes are the plant
There are a few legumes which possess additional features
which offer promise for ruminant nutrition and health as well as reducing
greenhouse gas emissions. These features
include tannins, polyphenol oxidase and protease enzymes. Sainfoin holds particular promise for alkaline
and drought prone soils.
Condensed tannins are a group of fabulous compounds that are
found in some forage legumes including birdsfoot trefoil. Sainfoin, sulla and
the flowers of trifolium species. Total
concentrations of these compounds depend on the variety, plant organ and
The role of these condensed tannins in reducing protein
degradation in the rumen is well documented.
By forming bonds with dietary proteins, condensed tannins generally slow
the rate of protein degradation during fermentation in the rumen, and as such
will reduce losses associated with rumination.
What is not yet fully understood is which types of condensed tannins
create optimal degradation rates. For
example, high concentrations of condensed tannins in trefoils may be too
potent, as cattle cannot utilise its dietary protein fully, as such, it is
excreted and results in high faecal N contents.
What does all this mean?
Grass clover mixes with 30-50% of legumes in the mix seems
to be an optimal system. These yield
high amounts of N from biological fixation (symbiosis), generate high forage
yields of high nutritive value, which generates high voluntary intakes and
livestock performance and at the same time they minimise the risk of N losses
to the environment. The big challenge
for legume based grassland husbandry systems however will be to maintain the
proportion of legumes within this optimum range.
As a component of mixed grass legume sward, forage legumes
offer important opportunities for tackling future agricultural challenges. The great potential of legumes for
sustainable intensification is related not just to one specific feature, their
strength stems from the fact that several of their features can act together on
different “sites” in the soil plant animal atmosphere system. The multiple advantages benefit the whole
grassland husbandry system through reduced dependency on fossil energy and
industrial N fertiliser, lower nitrate and GHG emissions, into the environment,
lower production costs, higher productivity and protein self-sufficiency.
Legumes generate these benefits at the land management unit
level, and although these benefits are brilliant, there are some limitations
and further research is needed to make sure that we as farmers have all the
facts and can make best use of them within our swards and rotations.
To read the full paper please click here. Are you managing to hit 30% legumes in your
sward? Let us know how you manage their
persistence and graze them to optimise productivity. FCCT would love to know how you manage them.