Integrating tannin-rich legumes into tall fescue pastures to strengthen the sustainability of beef cattle production in the southern United States

Commodities

Practices

Tall fescue
(Schedonorus
arundinaceus [Schreb.]
Dumort., nom. Cons.; TF) is a dominant, perennial cool-season
forage that covers approximately 15 million hectares of the
southern United States and is commonly infected with the
endophytic fungus Epichloë
coenophialum ⁽¹⁾. Due to this
fungus, animals that graze on TF pastures usually display several
symptoms associated with reduced animal performance, collectively
known as fescue toxicosis ⁽²⁾. However,
despite its toxicity, TF remains a dependable and desirable
forage for many ruminant livestock producers, since it is easy to
establish, highly persistent, and adaptable to diverse climatic
conditions with limited management
⁽³⁾. Therefore,
reducing the effects of TF toxicosis has been a topic widely
investigated. 

 One of the possible
alternatives to attenuate the effects of fescue toxicosis would
be to use compounds that would inhibit its action. Condensed
tannins (CT) possess a strong binding affinity with steroidal and
protein-like alkaloids that are produced by the endophytic fungus
in TF, which might potentially reduce the post-ingestion effects
of fescue toxicosis ^(4;
5). Further, CT is
effective in decreasing greenhouse gas (GHG) emissions,
increasing N use efficiency, and shifting N loss through the
urine to more stable N complexes in the feces
⁽⁴⁾. However, in
most investigations, CT is used in its isolated form or in
grazing systems with plants of hard establishment
⁽⁶⁾, both of which
are generally impractical for beef cattle producers. In forest
systems, tannins in plant litter have been shown to slow rates of
nutrient cycling by supplying more recalcitrant C substrate,
binding with proteins in the soil, inhibiting N mineralization,
and enhancing organic matter persistence in the soil
^(7;
8). Due to high affinity
with some minerals, such as Al ⁽⁹⁾ and Fe
⁽¹⁰⁾, tannins
might also increase availability of other minerals to the
plant ⁽¹¹⁾.  

 Although many studies
have investigated the effects of CT on the animal, little is
known regarding its dynamics in the soil of pasture systems.
Therefore, we propose a systems-based applied research and
education approach to incorporate CT into a TF grazing scheme as
a strategy to enhance the sustainability of southern beef
production systems. We will evaluate the effects of two different
CT-rich legumes (birdsfoot trefoil [BFT;
Lotus corniculatus
L.] and crownvetch [CV;
Securigera varia
{L.} Lassen]) seeded into TF in a
grazing trial focusing on the interaction of plants, soil, and
animals. At the animal level, we will evaluate performance,
toxicosis incidence, methane emission, nitrogen utilization
efficiency, changes on rumen microbiota, and overall health of
the animals. At the plant level, we will be evaluating herbage
responses, biological nitrogen fixation, and yield. Finally, at
the soil level, we will evaluate soil microbial communities,
nitrogen utilization efficiency, GHG emissions, and soil organic
matter. Research information from this proposal will then be
delivered to producers as a management tool in sustainable beef
cattle systems in the region through workshops, online courses,
web-based content, handouts, and farmer demonstrations on field
days. 

Our long-term goal is to
ensure economically and environmentally sustainability of beef
production in the southeastern U.S. through an integrated system
that considers soil, plant, and animal altogether. Our
overall objective
is to evaluate the incorporation of
CT-rich plants into a TF grazing scheme as a strategy to reduce
farmers inputs, as well as any detrimental effects from grazing
systems. Our central
hypothesis is that the
inclusion of CT-rich plants will reduce TF toxicosis, production
of enteric methane, and nutrient input into the soil while
augmenting productivity of beef cattle, soil health, and nitrogen
utilization efficiency. To accomplish this, we propose
four specific
objectives: 

Specific Objective 1: Evaluate the
effect of perennial, cool-season, CT-rich legumes incorporated in
TF pastures on herbage responses and beef cattle
performance.  

When animals graze a diverse
vegetation containing plant secondary metabolites, the different
chemicals ingested in the process improve animal performance
while increasing the resilience of agroecosystems
(72). Therefore, the goal for the
research under this specific objective is to evaluate how the
inclusion of CT-rich legumes incorporated into TF pastures can
affect grazing beef cattle performance and herbage responses.
Our hypothesis
is that the inclusion of CT-rich
legumes will increase the intake of TF, and consequently, gain of
animals. Simultaneously, we hypothesize that
herbage responses will also be improved due to better biological
nutrient fixation attributed to the inclusion of CT-rich legumes.
Our approach
will use the incorporation of BFT and
CV into TF pastures in a grazing study. Our
rationale
for this objective is that CT present
on BFT and CV may potentially
boost performance in beef
cattle production, while still allowing a higher fixation of
nitrogen by those legumes. Our expected outcome at
the end for this objective is that the inclusion of CT-rich
plants will increase carrying capacity, increase average daily
gain, increase herbage mass and quality, and increase gain per
unit area. With that, our overall outcome is
to provide a more productive grazing system for beef cattle
producers while still reducing their
inputs.  

Specific Objective 2: Evaluate the
role of CT-rich legumes in mitigating TF toxicosis and
CH4
emissions, and nitrogen utilization
efficiency in beef cattle. 

Due to its toxicity, TF can be
detrimental to beef cattle. CT possess a strong binding affinity
to the toxic component in TF, which might potentially reduce
effects of fescue toxicosis (4;
5). Meanwhile, CT also can
decrease GHG emissions and increase N use efficiency
(4),
which can all lead to a higher production of beef cattle. With
that, the goal
for this specific objective is to
evaluate how the inclusion of CT-rich legumes can affect TF
toxicosis, carbon loss through methane, and nutrient utilization
dynamics of beef cattle. Our hypothesis is that
the inclusion of CT-rich legumes will help lessen the effects of
TF toxicosis, while decreasing CH4 enteric emissions and
increasing N use efficiency. Our approach for this
objective will use a replicated grazing study to assess animal
dynamics. The rationale is that CT
will bind to the alkaloids present in TF and reduce
post-ingestion effects of TF toxicosis, while also reducing
methane synthesis and N excretion due to inhibition of
methanogens and binding to proteins, respectively. Altogether,
our overall
outcome at completion of
this objective is to develop grazing management recommendations
for TF pastures in association with CT-rich plants that will
provide both economically and environmentally sustainable
practices.   

Specific Objective 3: Evaluate soil
microbial communities, nitrogen utilization efficiency, GHG
emissions, and soil organic matter of TF mixed with cool-season,
CT-rich legumes. 

Tannins in plant litter have been
shown to slow rates of nutrient cycling by supplying more
recalcitrant C substrate, binding with proteins in the soil,
inhibiting N mineralization, and enhancing organic matter
persistence in the soil (7;
8). Also, the affinity of CT to
alkaloids can shift the N metabolism site, reducing the N
excreted in the urine, and improving the amount of N excreted by
feces. This process may improve the N cycling in the soil,
mitigating the N leaching. With that, the
goal
for this specific objective is to
evaluate how the inclusion of CT-rich legumes can affect soil in
organic matter, GHG emission, and nutrient utilization dynamics
by soil microorganism. Our hypothesis is that
the inclusion of CT-rich legumes will help the reduction of N
excretion by urine, decreasing GHG soil emissions and increasing
N use efficiency. Our approach for this
objective will use static chamber to evaluate GHG
emission and soil measurements in TF
and legume mixtures grazing pasture. The
rationale
is that like animal rumen, CT will
bind to the alkaloids present in the soil and facilitate the
metabolism by microorganism. Thus, our
overall outcome
is with inclusion of CT-rich legumes
into TF pasture will improve the microorganism performance into
soil via excreta, facilitating the N cycling and mitigating
GHG. 

Specific Objective 4: Create and
extend educational products on managing TF pastures with CT-rich
legumes as a practice to reduce GHG emissions and increase soil
health.  

All information obtained from the
previous objectives is only relevant if transmitted to forage and
livestock farmers. Therefore, the goal of this
objective is to translate the research results obtained from
Specific Objectives 1, 2 and 3 into accessible educational
materials and training for beef cattle producers which will
enhance environmental and economical sustainability. Our
hypothesis
is that the dissemination of
educational resources to producers will enhance the potential for
adoption of the sustainable practices explored in this project.
We will approach
this objective using educational
products, farmer demonstrations, field days, and online resources
to disseminate the importance of using CT-rich legumes on TF
pastures to strengthen the sustainability of beef cattle
production.  The rationale is that
those techniques can only be put into practice if we enhance the
awareness and knowledge of the end users on this matter.
Therefore, our expected
outcome is that farmers
will start to implement the practices on this project. Upon
completion, our overall
outcome is to provide a
more accessible resource for sustainable beef cattle
producers.