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A publication of the University of the Virgin Islands Agricultural Experiment Station January, 2002
INTRODUCTION
Pastures typically account for the
largest proportion of land use in the
tropics (e.g.. 80% of land use in the
U.S. Virgin Islands; USVI). Proper
management of pasture lands, then.
is critical to sustainable land use and
overall success of animal production
enterprises. For animal production.
assuming the right animal type.
adequate water source, and good
infrastructure (i.e.. fencing and
shade), the main focus of pasture
management is usually on pasture
productivity, nutritive value, and
longevity.
Pasture productivity is depen-
dent on seasonal rainfall, soil and
pasture type, weed competition and
composition, and number of live-
stock carried. Fertilizer manage-
ment, weed control, selection and
introduction of new plant species
(i.e., higher yielding or more
desirable growth characteristics)
and re-seeding are some agronomic
techniques that have been used to
increase pasture productivity.
Pasture quality is also dependent
on seasonal rainfall, soil and pasture
type, amount of forage present and
maturity of the plant, and the number
and type of livestock grazed.
Fertilizer N applications and addi-
tion of forage legumes to pastures
have been used to enhance nutritive
value.
Pasture composition also plays
Pasture management makes economic and environmental sense.
an important role in productivity and
quality. Sustained productivity and
pasture longevity, however, are
strongly dependent on the intensity
and frequency of grazing.
The objective of this factsheet is
to provide a guide to grazing
managers for maintaining long-tenm
sustainability of their pasture re-
sources.
GRAZING MANAGEMENT
CONCEPTS
The Forage and Grazing Termi-
nology Committee (1992) defined
several terms in grazing manage-
ment. The manipulation of livestock
grazing to accomplish desired re-
sults (i.e., high levels of production
and long-term persistence) best
describes grazing management.
Main variables in grazing manage-
ment are stocking rate, stocking
density, and grazing method. Stock-
Ing rate is the number of animals per
unit area (related to the total area that
the animals wil graze). Stocking
density is the number of animals per
unit area at a given point in time. If
20 cows graze a 10-acre area. either
continuously or rotationally, the
stocking rate is two animals per acre
Factsheet: Managing Pasture Resources
How close to graze is key to maximizing productivity of guineagrss.
(20 animals per 10 acres). However,
the stocking density is 40 animals
per acre if the 10 acres is subdivided
for rotational grazing into 20
paddocks of 0.5 acres each (20
animals per half-acre paddock at any
given moment in time). Grazing
method is a defined technique of
grazing management (either con-
tinuous or rotational), that can be
applied over a defined period of time
without pasture deterioration. Graz-
ing intensity (how close to graze) is
a stocking rate for a pasture, or a
plant stubble height when cattle are
removed from the grazed pasture.
Grazing frequency (how often to
graze) is the length of the rest
periods between grazing. Grazing
pressure, the unit of animal
liveweight per unit of forage dry
matter and herbage allowance (kg of
forage per kg of animal weight) are
also important to give a complete
picture of the balance between
pasture productivity and stocking
rate. The closeness of grazing and
how often a pasture is grazed are
perhaps the most important deci-
sion-making tools available to graz-
ing managers.
FORAGE AND
LIVESTOCK NEEDS
Recognizing both forage and
livestock needs is important to
developing effective grazing man-
agement systems. Matching what
the forage plant can provide and
what the livestock need nutritionally
should be the ultimate goal of
grazing managers.
Adequate quantity (amount avail-
able) and nutritive value (crude
protein and digestibility) of pastures
are major livestock needs. Overgraz-
ing not only affects the pasture, but
also reduces animal performance
because of limited forage. Maturity
affects the nutritional value of
pastures. Grazing a pasture fre-
quendy may ensure that animals
have access to young regrowth and
high quality forage, but if the plant is
not adapted to this type of manage-
ment it may severely limit pasture
regrowth and may result in pasture
deterioration. In contrast, infrequent
grazing may result in large quantities
of forage being available for
livestock, but it may be so low in
nutritive value that animal perfor-
mance is affected.
When grazed, forage plants must
maintain enough leaves to produce
energy for regrowth, or stored
reserves to provide that energy. If
frequently defoliated, forages may
not have enough time to grow new
leaves and replenish their supply of
reserves before another grazing
event. The result is that after each
grazing the plant has less reserve
energy than before, and eventually
its reserves are depleted. Appropri-
ate rest periods allow the forage
plant to accumulate reserves before
another grazing event.
Differences in the requirements
of various classes of livestock are
also important. Mature guineagrass
(Panicum maximum var. Jacq.) may
be a very adequate feed fora dry beef
cow, but it may not be adequate for a
University of the Virgin Islands Agricultural Experiment Station
Electro-net fencing works well for control of rest periods in grazing management.
growing lamb or heifer.
The key to maximizing produc-
tivity of pastures and reducing losses
from animal impacts is understand-
ing that pasture species differ in their
tolerance to grazing. Also there is a
give and take between pastures and
livestock that can be considered
when prescribing a level of grazing
management that best addresses
those needs.
GRAZING MANAGEMENT
TECHNIQUES
Grazing managers usually
determine before-hand what forages
to graze (i.e., adaptability of the
forage to their location), what inputs
(i.e., weed control, fencing, and
fertilization) are more feasible, and
what type of livestock will do the
grazing. Knowing the needs of the
farm enterprise, important decisions
to be made by grazing managers are
the grazing intensity and frequency
of grazing to be applied on a
particular forage.
An important decision when
managing your pasture is how close
to graze. The stubble height to graze
varies among pasture species. The
stubble height selected will deter-
mine whether the plants will have
enough leaf or living buds available
for regrowth after each grazing
event. The closeness of grazing can
be determined by the stocking rate
that you choose or by the decision to
graze to a selected stubble height
[e.g., 6" (15-cm) from ground level].
Bunch-type grasses (i.e., guineagrass)
should be grazed to a taller stubble
height than low-growing grasses
(i.e., bahiagrass). If guineagrass is
grazed too closely the stand can be
damaged. If not grazed closely
enough, animal production per acre
will be limited, and it is likely the
nutritional value of the forage will be
reduced.
Sensitivity of the pasture to
overgrazing and sensitivity of the
animals to periods of insufficient
forage are critical. For example, in
the USVI, hurricanegrass
(Boithriocloapertusa) can be grazed
considerably closer than guineagrass.
If there is a shortage of pasture and
both grasses are grazed to the
ground, hurricanegrass will regrow
but the guineagrass stand will not.
Each situation requires thought and
the knowledge of how both the
forage in your area and animal will
respond. No one guideline can be
used for all forages or all types of
animals.
Other important factors affect-
ing the choice of grazing intensity
are related to the amount of
flexibility that a grazing manager
has to adjust animal numbers or to
supply hay. Under conditions where
pasture is the only source of feed and
the number of animals cannot be
profitably adjusted by buying or
selling, then stocking should be done
conservatively. If there is potential
and profit in conserving forage as
hay, or adjusting animal numbers,
then there is less risk in stocking at a
rate that would be appropriate for the
average year.
When considering how often to
graze your pastures, the method of
stocking, either continuous or rota-
tional, plays an important role.
Rotational stocking indicates that a
pasture is divided into two or more
subunits (paddocks), and the pad-
docks are regularly grazed and
rested in an orderly sequence (e.g.,
7-d grazing and 28-d rest period).
Continuous stocking occurs when
the pasture is not subdivided and
cattle are given continuous access to
the entire area (no rest period from
grazing).
Rotational stocking may be
preferred over continuous because
the grazing manager can control the
rest periods. Some advantages of
rotational grazing are that longevity
of the forage is usually improved,
there is timely utilization of the
forage, and the grazing manager has
options for stockpiling and conserv-
ing forages (i.e., hay production). In
addition, the manager sees his
livestock and pasture more often and
can manage both more effectively.
Continuous stocking may be
preferred over rotational because it
requires less initial expense in terms
of fencing and water lines and there
are fewer decisions to be made.
Also, there is less variation in the
nutritional value of the animal's diet
from day to day than under a
rotational system, because animals
are more selective when continu-
ously stocked.
There is, however, a give and
take between how often and how
close to graze forages. If a forage is
grazed very closely, then it will
generally require a longer rest period
than if a taller stubble was left.
Likewise, leaving a taller stubble
may allow more frequent grazing
than if plants were grazed closely. It
is critical that we can predict how a
plant will respond to the manage-
ment imposed, so that we do not
destroy pasture stands.
ECONOMICS OF
GRAZING METHODS
Additional costs for rotational
stocking include fencing (usually
movable electric fencing) and a
battery (usually a solar panel). These
costs amount to around $750 for one
acre, assuming the pasture is divided
into three paddocks. Since equip-
ment lasts for several years, these
costs should be "annualized" (a
simple way to annualize costs is to
divide the equipment cost by the
number of years of useful life).
Assuming a 10-year equipment
life, the annualized equipment
costs amount to $75. Another cost
associated with rotational grazing
is labor for moving fences. This
could amount to $150 (4 hrs./acre/
month) for a 6-month production
season, resulting in total additional
costs of $225 for the rotational
system. However, rotational graz-
ing can preclude the need for
supplemental forage which is
generally needed in a continuous
grazing system. If rotational graz-
ing is used, this could result in cost
savings of $275 per acre (mostly in
the form of additional labor to
harvest forage). Since the cost
savings are greater than the
additional costs, rotational grazing
can result in additional income of
$50 per acre per year. If additional
animal weight gains result from
the rotational grazing system, as is
likely, then the monetary gains
could be even greater.
CONCLUSIONS
Taking care of your pastures
makes economic and environmental
sense. Good pasture management is
key to higher profits and healthier
natural resources. It is a powerful
tool to influence plant and animal
performance in forage-based live-
stock systems. For this tool to be
used effectively, however, the graz-
ing manager must understand what
the plant provides nutritionally and
what the animal needs nutritionally,
and then choose a management that
balances the two. The most impor-
tant choices to be made in any
pasture management system are how
close and how often the pastures are
going to be grazed. These choices
affect pasture performance, which,
subsequently determines how well
the animals will perform. The key to
maintaining productive pastures and
minimizing animal impacts is recog-
nizing that forage plants have
specific requirements for persis-
tence, and then prescribing a level of
grazing management that best ad-
dresses those needs.
Choice of pasture management
will affect pasture productivity,
forage nutritive value, and longev-
ity. Profitability of enterprises that
are based on grazed pastures will be
greatly influenced by the way in
which pastures are managed, t keeps
the seed moving.
REFERENCES
SoUlenberger, LE., and C.G.
Chmbliss. 1989. Grazing management
of improved pastures. p. 42-44. In Beef
Cattle Short Course Proc., Gainesvlle,
FI, 3-5May1989. Inst FoodAgric. ScL,
Univ. of Fla., Gainesville, FL
The Forage and Grazing Terminol-
ogy Committee. 1992. Terminology for
grazing lands and grazing animals. J.
Prod Agric. 5:191-20.
Prepared by E. Valencia, Assistant Professor, University of the Virgin Islands; L.E. Sollenberger,
Professor, University of Florida; and Gerasd4.,E pfessor, West Virginia University.
Issued by the University of the Vir j _ndTlic I al Experiment Station, James Rakocy,
Director. a
Funding for this Factsheet was
and Education (SARE) LS 99-107.
the Sustainable Agriculture Research
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