Group Title: Bulletin - University of Florida, Agricultural Experiment Station ; 884
Title: Management of stargrass pastures for growing cattle using visual pasture characteristics
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 Material Information
Title: Management of stargrass pastures for growing cattle using visual pasture characteristics
Series Title: Bulletin University of Florida, Agricultural Experiment Station
Physical Description: 7 p. : col. ill. ; 28 cm.
Language: English
Creator: Pitman, William Don, 1949-
Publisher: Florida Agricultural Experiment Station, Institute of Food and Agricultural Sciences, University of Florida
Place of Publication: Gainesville Fla
Publication Date: 1991
 Subjects
Subject: Grasses -- Varieties -- Florida   ( lcsh )
Pastures -- Florida   ( lcsh )
Grazing -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Bibliography: Includes bibliographical references.
Statement of Responsibility: W.D. Pitman.
General Note: Caption title.
General Note: "October 1991."
Funding: Bulletin (University of Florida. Agricultural Experiment Station) ;
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Bibliographic ID: UF00086511
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 25054373
issn - 0096-607X ;

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4D October1991 Bulletin 884

INSTITUTE OF FOOD AND AGRICULTURAL SCIENCES

Management of Stargrass Pastures for

Growing Cattle Using Visual Pasture

, L,'I.i Characteristics
W.D. Pitman*
Florida Agricultural Experiment Statior / Institute of Food and Agrjiqltural Scinces / University of Florida / J.M. Davidson, Dean


Background 1 university of
'McCaleb' stargrass (Cynodon aethiopiciis) was
the first stargrass cultivar developed and released
for use in Florida. The recommended grazing
management procedures were rather broadly stated
to include 1) leave a 6 to 10 inch stubble, 2)
rotationally graze pastures, 3) fertilize according to
amount of forage production desired (responses to
as much as 100 pounds N per acre per application
were noted), and 4) substantial fall fertilization is
required for late-season production (Hodges et al.,
1975). Although McCaleb stargrass was recognized
as having forage quality superior to bahiagrass, it
was reported to be lower in quality than
digitgrasses.
'Ona' stargrass (Cynodon nlemfuensis) was
subsequently released as a higher quality stargrass
cultivar with forage quality similar to that of the
digitgrasses. Recommendations for grazing Ona
stargrass suggested that this cultivar could occa-
sionally be grazed to a low stubble, but generally it
should be grazed to a 5 to 10 inch stubble using
rotational grazing with 3 to 5 weeks between
grazing periods (Hodges et al., 1979). It was
further suggested that pastures fertilized appropri-
ately in May could carry three head of yearling
cattle per acre through the summer, although
continued heavy grazing would reduce productivity.
Recommendations for two recently released culti-
vars, 'Florico' and 'Florona' stargrass (Cynodon
nlemfuensis), include the use of regrowth periods of
4 to 5 weeks between grazing periods (Mislevy et
al., 1989a and 1989b). A decrease in forage quality
with increased length of the regrowth period was
noted, while persistence of the grass stand was
improved by longer rest periods. Emphasis was
given to the plant height above the stubble, which


* *Associate Professor of Agronomy at the Agricultural
Research and Education Center at Ona, Florida 33865.


Fioras reco mended at 6 to 18 inches to maintain
plant persistence and high yields of quality forage.


Under commercial use, stargrass pastures have
been subjected to a broad range of management
procedures with a corresponding range of re-
sponses. Several management approaches, which
may be successful with other pasture grasses such
as bahiagrass, have resulted in unsatisfactory
animal performance and loss of stargrass stands.
Long-term use of heavy grazing pressures and low
or infrequent fertilization have proven to be unac-
ceptable methods of managing stargrasses. Obser-
vations of appropriately grazed stargrass pastures
may give the appearance of excessive herbage
accumulation and waste of forage. However,
stocking to use all of the season's growth rather
than allow accumulation of a stubble layer through
the growing season has three major detrimental
effects. It forces cattle to graze a higher proportion
of the low quality stems which reduces performance
of individual animals (lower gains of young growing
animals and lower milk production of lactating
cows). It results in reduced forage production
because an excessive proportion of the leaves,
which provide the organic compounds for new
growth through photosynthesis, are removed. It
also opens the stargrass stand to invasion by other
plants and eventually leads to a sparse, weedy,
unproductive pasture which may respond poorly to
fertilization since weeds may use a high proportion
of the applied nutrients.
At the other extreme, stargrass pastures on
relatively fertile sites under low grazing pressures
have developed such massive accumulations of
stemmy growth that only small proportions of the
herbage were actually grazed. This potential for
excessive accumulation of unpalatable, stemmy
growth limits the length of time that stargrass
pastures can be allowed to grow between grazing
periods. Regrowth periods longer than 4 or 5 weeks
between grazing cycles can result in excessive stem








accumulation and low proportions of herbage
grazed.
Observations of stargrass pastures subjected to
different grazing pressures and management
procedures have resulted in identification of some
visually distinct characteristics, primarily reflect-
ing leafiness, that indicate the level of animal
performance that will likely be obtained.

Experimental procedures
The approach to stargrass management sug-
gested in this paper is the result of observations of
a number of stargrass pastures under various
management strategies from 1980 through 1990 in
addition to three specific grazing experiments. One
experiment has been described previously (Pitman
et al., 1984). Brief descriptions of the additional
two experiments follow.

Experiment 1
Three stocking rates were imposed on Ona
stargrass pastures during two consecutive growing
seasons. Stocking rates were 0.8, 1.6, and 2.4 head
of yearling steers per acre. A randomized block
design with three replications was used. Each
block consisted of 5 acres. Pastures were fertilized
with 450 pounds per acre of a 16-8-8 fertilizer in
April and August of the first year and in May of the
second year. Pastures were grazed continuously
from April 21 to October 6, 1982 by steers initially
averaging 590 pounds per head. In 1983, grazing
was from June 7 to September 20 by steers averag-
ing 670 pounds per head initially.

Experiment 2
Two stocking rates, 1.6 and 3.2 head of yearling
steers (with average initial weights of 630 pounds)


per acre, were compared on continuously grazed
Ona stargrass pastures from May 17 until July 28,
1989 when both treatments were continued at the
same stocking rate of 1.6 head per acre until
August 29. Pastures were fertilized with 450
pounds per acre of a 16-8-8 fertilizer in late March.
The experimental design was a completely random-
ized design with two replications.

Results

Animal responses
In Experiment 1, as stocking rate was increased
there was a corresponding decrease in performance
of individual animals (average daily gain) and a
corresponding increase in total gain per acre (Table
1). The same pattern was obtained in Experiment 2
during the May to July period when the higher
stocking rate produced lower average daily gain but
greater gain per acre than did the lower stocking
rate (Table 2). Maximizing total gains per acre
may be desirable in situations where lower indi-
vidual animal performance is acceptable. In other
situations, such as heifer development, individual
animal performance may be so critical for a desired
objective, such as early breeding, that maximum
individual animal gain is desirable. From animal
performance levels at a range of stocking rates, the
economic optimum stocking rate can be calculated
as described by Hildreth and Riewe (1963) and
Bransby (1989). This economic optimum stocking
rate will differ for various combinations of buying
and selling prices for cattle, costs of other inputs,
etc. With stargrass pastures, an additional critical
factor must be considered. In Experiment I at the
high stocking rate, two years of grazing resulted in
sufficient pasture deterioration through loss of
stargrass and invasion by weedy species that the


Table 1. Effect of stocking rate on performance of yearling steers and visual appearance of stargrass pastures during the 1982 and
1983 growing seasons.
Stockingt Animal days Average1 Totai Pasture
rate of grazing daily gain gain appearance
head/acre days/acre pounds/head/day pounds/acre
0.8 109 1.77 194 green and leafy with only a few
stems noticeable
1.6 219 1.47 322 the upper leaf layer has been
removed with stems visibly
interspersed among the leaves
2.4 328 1.23 405 stems are prominent across the
pasture surface with leaves
primarily below this sparse
surface layer of stems
r Average initial weight of steers was 590 pounds in 1982 and 670 pounds in 1983.
t Linear responses of average daily gain and total gain to stocking rate.








Table 2. Responses in gain of yearling steers to adjustment of
stocking rate in 1989.
Stocking rate Average daily gain Total gain
IMay-July August May-July August May-July August
---head/acre--- --pounds/head/day-- ----pounds/acre----
3.2 1.6 0.97 1.33 278 85
1.6 1.6 1.30 1.29 188 83
tAverage initial weight of 630 pounds.

trial was discontinued. Stands of stargrass can be
lost at stocking rates that result in maintenance or
even low levels of gain of grazing cattle. This is a
distinct contrast to bahiagrass where cattle may
actually be starved before excessive stand loss
occurs due to overstocking.

Pasture responses
Along with the responses in animal performance
associated with different stocking rates, grass
stands developed distinct characteristics in each
pasture treatment. Under light stocking rates, and
at the start of grazing under higher stocking rates,
pastures were characterized by an upper layer of
leaves with a green appearance across the pasture.
At the intermediate stocking rate, the upper leaf
layer was gradually grazed, and pastures had a
predominantly green appearance with interspersed
brown stems across the pasture surface. At the
highest stocking rate, pastures developed a visible
upper layer of stems with cattle selectively grazing
leaves from lower levels of the grass stand. With
the leafy pasture surface layer, both diet quality
and quantity consumed per animal were maxi-
mized. As the grass stand was grazed down, the
proportion of stem increased (especially in the
surface layer), which resulted in progressively more
effort by the cattle to select the more palatable
leaves. Such changes in accessibility of selectively
grazed pasture components typically result in
reductions in both quantity of forage consumed by
each animal and diet quality leading to lower
average daily gains.

Potential applications
Although maximizing individual animal perfor-
mance of a mature cow herd is not usually an
economical objective, such an objective may be
appropriate for some classes of cattle. In a rota-
tional grazing scheme for a cow herd on stargrass
pastures, forward creep grazing (allowing the
calves to creep graze on the next pasture to be
Grazed by the cow herd) could provide substantial


benefits. Also, weaned calves could be appropri-
ately stocked for near maximum gains on stargrass
pastures in late summer and autumn. Even first-
calf heifers, which need some extra opportunity to
gain condition and improve the probability of
rebreeding, may benefit from stocking rates low
enough to allow maximum individual animal
performance.
Steer calves which were weaned in September
and stocked at 1 head per acre on rotationally
grazed Ona stargrass pastures averaged 1.6 pounds
per day during November over three successive
years (Pitman et al., 1984). Individual gains of at
least 1 to 1 1/2 pounds per day can be anticipated
for calves after the weaning period, providing an
opportunity for development of replacement heifers
from weaning in late summer or early autumn until
frost. After frost, consumption of stargrass is
typically very low, even by mature cattle, resulting
in unacceptable levels of performance.
During the spring season, average daily gains of
2 pounds per head reported by Pitman et al. (1984)
include some compensatory gains from low winter
performance. Gains on stargrass pastures at
appropriate stocking rates during spring and early
summer can be expected to approach this level.
Performance of young growing cattle in late sum-
mer often drops drastically on stargrass pastures
during periods of frequent rainfall, high tempera-
tures, and pasture flooding. Weight losses may
occur during such periods in extreme cases, even
with intensive pasture management. Thus, low
gains in mid summer (1/4 pound per head per day
in August ) combined with the high spring gains
noted above gave gains throughout the growing
season of slightly over a pound per head per day
under rotational grazing with a flexible stocking
rate adjusted to maintain the desired grazing
pressure. Considerably higher daily gains are
shown in Tables 1 and 2 involving summer seasons
with less adverse wet periods. Thus, grazing
pressure, season of the year, and weather condi-
tions in a particular season all influence perfor-
mance of young growing cattle on stargrass pas-
tures. Of the factors involved, grazing pressure is
the most readily manipulated for improved animal
performance. Daily gains of individual animals can
be maximized for a particular season by visual
appraisal of pastures and appropriate adjustments
in grazing pressure. This maximum daily gain will
usually vary from 1 1/4 to 2 pounds per head per
day during autumn, spring, and early summer.
Years with high rainfall and high temperatures in
mid-summer may provide no opportunity for gain








under any grazing pressure for limited periods.
Except during these excessively hot, wet periods
and following frost, appropriately managed
stargrass pastures provide an option for growth of
young cattle in peninsular Florida.

Grazing behavior
Potential maximum gains are affected by both
the pasture and the grazing animal. Although
Florida pastures typically provide limitations to
animal performance before the genetic potential of
grazing livestock is even approached, some animal
factors deserve consideration. As stargrass pas-
tures are grazed down by a herd of cattle, grazing
by individual animals generally becomes more
aggressive. More effort is required to obtain
acceptable forage in each bite. Stems are avoided
and may even be manipulated (nosed out of the
way) in the grazing process. Length of time spent
grazing each day may also increase. Cattle which
have not been through this conditioning process as
the pasture is grazed down are typically at a
distinct disadvantage if added to the herd in a
heavily grazed stargrass pasture from a different
pasture type. Such a conditioning response is
illustrated in Experiment 2 where cattle in both
treatments made similar gains during August
when stocking rates were also the same (Table 2).
Pastures which had been subjected to a higher
stocking rate from May through July did not
recover to the same forage availability or degree of
leafiness as those previously grazed at the lower
stocking rate. More aggressive grazing by cattle in
pastures which had previously been subjected to
the heavy stocking rate allowed cattle in that
treatment to gain as well in August as those which
had previously been at the lower stocking rate.
This was possible because reduction of the stocking
rate allowed more forage per animal than was
available prior to the stocking rate reduction (even
though available forage and leafiness were still less
than in the pastures initially stocked at the lower
stocking rate). Thus, cattle responded to increased
forage availability within the pasture as the
stargrass grew. This conditioning effect should be
considered in moving cattle from pasture to pas-
ture, especially individuals from herd to herd.
Adding replacement heifers to the cow herd from a
lightly stocked pasture to a heavily grazed
stargrass pasture may result in early weight losses
that are difficult to overcome. Such poor perfor-
mance may occur even though similar cattle, which
have been conditioned to the pasture, perform
satisfactorily. Gradual conditioning of replacement
heifers to lower forage availability could be an


important management tool for cattle on stargrass
pastures.

Pasture characteristics
Obvious pasture appearance associated with
various levels of animal performance are described
in Table 1. These pasture characteristics were used
to adjust the number of grazing animals in the
experiment described by Pitman et al. (1984). They
can be used in practice as indicators of degree of
grazing pressure which may indicate when to
rotate in a rotational grazing system, when to
fertilize for additional forage production, or when to
adjust numbers of grazing animals if high weight
gains are the objective. Use of rotational grazing
systems involving three or more pastures provides
the flexibility of increasing nitrogen fertilization
rates and rotating cattle sooner than originally
planned to overcome temporary forage shortages.
Under continuous grazing, the need to reduce
animal numbers or sacrifice individual animal
performance may occur with insufficient time for
other alternatives.
Figures 1 and 2 illustrate pasture appearances
from grazing which result in distinctly different
rates of gain. Although stems are obvious in both
pastures (especially due to the contrast in color of
the light brown mature stems and bright green
leaves of well-fertilized stargrass), a view across
the lightly stocked pasture (Figure 1) shows a
predominance of green leaves, while the predomi-
nance of brown stems on a heavily stocked pasture
is especially apparent at a distance from the
observer (as shown by the background in Figure 2).
The high leaf composition of the upper pasture
layer in Figure 3 provides the opportunity for
intake of high amounts of leafy forage which
produce maximum gains in individual animals.
Figure 4 illustrates stargrass pastures which result
in only slight reductions in individual animal gain
as rate of forage intake is reduced in an effort by
grazing animals to avoid consuming excessively
stemmy material. Figure 5 is representative of
pastures where positive gains can be made, but
they are reduced considerably from the maximum
as stems begin to dominate the pasture sward.
Observing pasture changes during grazing allows
conclusions to be drawn regarding anticipated
responses of grazing animals. If near-maximum
average daily gains are desired for young growing
cattle, pasture appearance should be maintained as
illustrated in Figures 1, 3, and 4. Low rates of gain
can be anticipated from pastures illustrated in
Figures 2 and 5. This may be appropriate for








































Figure 1. Light stocking rate at the end of the grazing period showing predominance of green leaves across most of the pasture
area.


Figure 2. Heavy stocking rate at the end of the grazing period with predominance of brown stems especially noticeable at a
distance.







mature beef cows, especially if calves are allowed to
creep graze in a leafier pasture. Heavier grazing
pressure than that illustrated in Figure 2 can
rapidly result in invasion by weedy species includ-
ing less productive grasses and unpalatable broad-
leaf weeds.
A stubble layer of stems will gradually build up
through the growing season in stargrass pastures
which are not overgrazed. Grazing pressures high
enough to prevent this stubble buildup also reduce
the amount of forage (plant material actually
grazed) produced and allow weed invasion (Mislevy
et al., 1989) in addition to lowering the level of
animal performance. The stubble, which contrib-
utes to stand vigor and plant growth, can be re-
moved by close mowing or burning prior to growth
in early spring. This removal of the stubble allows
light to reach plant crowns and stimulates early
spring forage production. The stubble of a
stargrass pasture should not be considered a forage
resource either during the growing season or in the
winter. It is a characteristic of a productive, well-
managed stargrass pasture.

References
Bransby, D. I. 1989. Justification for grazing
intensity experiments: economic analysis. J.
Range Manage. 42:425-430.


Hildreth, R. J. and M. E. Riewe. 1963. Grazing
production curves. II. Determining the eco-
nomic optimum stocking rate. Agron. J. 55:370-
372.
Hodges, E. M., F. T. Boyd, L. S. Dunavin, A. E.
Kretschmer, Jr., P. Mislevy, and R. L. Stanley,
Jr. 1975. 'McCaleb' stargrass. Florida Agric.
Exp. Stn. Circ. S-231.
Hodges, E. M., P. Mislevy, L. S. Dunavin, O. C.
Ruelke, and R. L. Stanley, Jr. 1979. 'Ona', a new
stargrass variety. Florida Agric. Exp. Stn. Circ.
S-268.
Mislevy, P., W. F. Brown, R. Caro-Costas, J.
Vincente-Chandler, L. S. Dunavin, D. W. Hall, R.
S. Kalmbacher, A. J. Overman, O. C. Ruelke, R.
M. Sonoda, A. Sotomayor-Rios, R. L. Stanley, Jr.,
and M. J. Williams. 1989a. Florico stargrass.
Florida Agric. Exp. Stn. Circ. S-361.
Mislevy, P., W. F. Brown, L. S. Dunavin, D. W.
Hall, R. S. Kalmbacher, A. J. Overman, O. C.
Ruelke, R. M. Sonoda, R. L. Stanley, Jr., and M.
J. Williams. 1989b. Florona stargrass. Florida
Agric. Exp. Stn. Circ. S-362.
Mislevy, P., F. G. Martin, B. J. Downs, and K. L.
Singer. 1989. Response of stargrass to grazing
management. pp. 1017-1018. Proceedings of
the XVI International Grassland Congress, The


Figure 3. Stargrass early in the grazing period with an upper layer of leaves available for grazing.





DOCUi1 TJ1iN


Figure 4. Stargrass under moderate grazing with leaves readily accessible to grazing livestock, but with stems within the grazed
layer of the pasture.


Figure 5. Stargrass heavily grazed with green leaves available for grazing, but intermingled with stems which reduce both the
amount and quality of forage consumed.





DOCUM1 ENY


French Grassland Society, Versailles Cedex,
France.
Pitman, W. D., E. M. Hodges, and F. M. Peacock.
1984. Grazing evaluation of perennial grasses
with yearling steers in peninsular Florida. J.
Anim. Sci. 58:535-540.

Summary
Young growing cattle can gain over a pound per
head per day on well-managed stargrass pas-
tures in autumn, spring, and early summer.
Stargrass pastures stocked for maximum gain per
acre will provide individual animal gain well
below the maximum.
Visual appearance of stargrass pastures provides
an indication of the relative rate of gain which
will be obtained.
A green, leafy top layer on a stargrass pasture will
provide the maximum opportunity for grazing
cattle to obtain high intake of quality forage and
maximum individual gain (Figure 3).


Scattered stems and runners across the top of a
stargrass pasture may result in only limited
reduction from the maximum individual animal
gain (Figures 1 and 4).
A stargrass pasture which is visually dominated by
stems (which give a dominately brown color to
the pasture) will provide individual animal gain
of young growing cattle considerably below the
maximum (Figure 5).
Although regrowth periods longer than 3 to 5 weeks
typically result in development of a stemmy
lower stubble layer and reduced pasture utiliza-
tion, gradual development of such a stubble layer
through the growing season is desirable for plant
vigor, forage production, and stand survival of
stargrass pastures.


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