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FORAGE AND NUTRITION Guide 2017
FORA
GE AND NUTRITION
Guide 20
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Multispecies swards with species from two or more
plant communities (eg. plants from legume or herb plant
communities) increase forage production with less chemical
inputs. The theory behind this is that `niche complementarity'
occurs when the competitive interactions between the species
present in the sward are weakened as individual species have
di erent growth habits and, therefore, use resources di erently
to maximise productivity over the growing season.
For example, plants can have varying rooting depth and,
hence, exploit the soil at di erent layers. PRG has relatively
shallow roots and, therefore, only utilises nutrients that are
available in the upper layers of the soil. However, when forage
herbs of di erent rooting depths are included, they can
retrieve micro and macro nutrients (phosphorus, magnesium,
potassium, sulphur, zinc and boron) from the deeper soil layers
and, in turn, make these nutrients available to the grazing
animal.
Mixtures can potentially use sunlight better than monocultures
through improved interception of light caused by di ering
growth habits of the di erent plants in the mix. Components of
pasture mixtures show additional nutritional complementarity
also. When legumes are included in the mixtures, there are
positive interactions between the legumes and the non-legume
species in relation to nitrogen produced by the legumes.
As well as this, multispecies swards have been found to
suppress weed species in swards compared to monocultures
which may be due to the more complete utilisation of
resources in the soil when more species are sown. Losses
from weed competition represent a significant waste of
resources (water and nutrients) in agricultural systems. In
addition, multispecies swards have been shown to improve
above ground and below ground biodiversity compared to the
conventional monoculture crops.
However, there are di culties with maintaining well balanced
mixtures as there is a tendency to lose key species from the
mixture over time which caused by grazing pressure. This
may partly explain the preference for grass monocultures in
agricultural systems as reseeding represents a significant
investment by the farmer.
Irish sheep production systems (largely mid-season lambing)
rely on grazed grass in the diet of the ewes and lambs. There
is tremendous scope to grow more high quality grass on sheep
farms, use it more e ciently, thus allowing increased stocking
rates, higher production per hectare and lower bought-in
feed cost. In light of the average stocking rate on sheep farms
being just over 7 ewes per hectare there is significant scope to
reduce the level of external inputs into these systems.
Multispecies swards used for sheep production have shown
some potential for improving growth rates in lambs in previous
work carried out in New Zealand. In addition, lambs fed herb
containing forages required less anthelmintic treatments
than those fed conventional grass pastures. Resistance to
conventional products for controlling intestinal parasites is
becoming a major problem for sheep producers so perhaps
there is potential for these multispecies swards that display
some anthelmintic properties.
With this in mind, four farmlets were established at UCD Lyons
Research Farm, in September 2014. Four sward treatments are
currently being investigated in this study: a PRG-only sward,
receiving 163kg N per hectare per year (kg N/ha/y); a PRG and
white clover mix at 90kg N/ha/y; a six-species mix at 90kg/N/
ha/year (PRG, timothy, red clover, white clover, plantain and
chicory) and a nine species mix at 90kg/N/ha/year (PRG,
timothy, cocksfoot, red clover, white clover, birdsfoot trefoil,
plantain, chicory and yarrow).
In 2015, each farmlet was stocked with 30 twin-rearing ewes
at a stocking rate of 12.5 ewes/ha (2.5 livestock units (LU)/ha
pre-weaning and 5.5 LU/ha post weaning). The sheep were
turned out four weeks after lambing in March and grazed until
the lambs reached a slaughter weight of 45kg liveweight.
Lambs were weighed fortnightly and average daily gain (ADG)
calculated.
Faecal egg counts (FEC) were measured fortnightly from each
individual lamb. Lambs were only dosed when the FEC of the
group exceeded a pre-defined threshold. Ewes were weighed
monthly and their body condition scores monitored on several
occasions throughout the production cycle. Ewes and lambs
rotationally grazed five paddocks per sward treatment.
Pasture herbage mass was measured before and after each
grazing event throughout the year. In addition, samples were
taken for separation into the di erent plant groups to allow us
to assess persistency of each species functional group over
time under intensive grazing. Herbage was measured weekly
and using grassland management software, in times of deficit,
lambs were supplemented with concentrates and similarly,
in times of surplus grass supply, paddocks were removed as
baled silage.
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PRG
PRG WC
six-spe-
cies mix
Sward type
W
eight (k
g)
nine-spe-
cies mix
Figure 1. The e ect of sward treatment on weaning weight of lambs (kg).