Driving directions
Linneus, Linn County
Grazing School
2007 Brochure
Workshops
Research
Faculty
News
Weather
Contact us
Superintendent
David Davis
21262 Genoa Road
Linneus, MO 64653
Phone: 660 895-5121
FAX: 660 895=5122
Email:
DavisDK@missouri.edu
|
This paper was published in the Proceedings 1996 AFGC
Annual Conference Vancouver BC, June 12-16, 1996.
SWARD CHARACTERISTICS OF BEEF FINISHING PASTURES
J.R. Gerrish, F.A. Martz, V.G. Tate1
Abstract
For cattle to successfully finish on pasture, abundant
high-quality forage must be available to the grazing
animals. Eighty-eight steers were finished on pasture
with grain supplementation ranging from 0 to 75 % of the
dietary energy supplied by grain. Pastures were
intensively managed, cool-season, grass-legume pastures.
Forage dry matter availability increased throughout the
grazing season. The quality of the pastures also
improved through the season, with crude protein (CP)
content increasing and acid detergent fiber (ADF) content
decreasing. Forage intake decreased at an average rate
of 1 lb for each lb of grain fed. Observed average daily
gains (ADG) were consistent with predicted ADG based on
forage plus grain intake levels.
Introduction: To successfully finish cattle on pasture,
forage quality must be high and forage availability
maintained at adequate levels to ensure optimal intake.
Blaser et al. (1977) suggest that energy intake will
limit performance of ruminants grazing cool-season
forages before protein or other nutrients. Energy
content of perennial cool-season forages is most affected
by maturity of the plant. Management of high energy
potential pastures must focus on maintaining plants in a
high quality, vegetative state. In this research we
examined trends in forage availability, pasture quality,
and voluntary forage intake.
Materials and Methods: A pasture-based, beef finishing
project was conducted at the University of Missouri -
Forage Systems Research Center in north-central Missouri
in 1995. Eighty-eight steers were assigned to four grain
feeding levels on pasture with each treatment replicated
twice. Grain feeding levels were expressed as the
percent of their total dietary energy intake supplied by
grain and were 0, 25, 50 and 75 % with the remaining
nutrients supplied by pasture. The pasture with steers
receiving no grain was stocked at 1.0 steer to the acre.
The pasture with steers receiving 25 % of their energy
from grain was stocked at 1.25 steers per acre. The
pasture with steers receiving 50 % of their energy from
grain was stocked at 1.5 steers per acre. The pasture
with steers receiving 75 % of their energy from grain was
stocked at 1.75 steers per acre (Table 1).
During the first phase of the experiment, April 22
to August 22, the supplement was cracked corn. During
the second phase, August 23 to October 30, the supplement
contained 70 % cracked corn and 30 % corn gluten feed.
Each treatment consisted of 8 acres which were
divided into six permanent paddocks (Fig 1). During the
grazing season, these were further divided with temporary
fences and animals were allowed to back graze the paddock
in order to access the water supply. Each subdivision
within a paddock provided the animals with 1 to 3 days of
feed depending on the season. Rest periods ranged from
10 to 35 days depending upon season and subdivision
within paddock. Pastures were clipped for seedhead
control in early June after cool-season grasses had
headed.
Table 1. Supplementation level, stocking rate, and number of
steers per treatment group in pasture-based finishing study.
================================================================
Supplementation Stocking Number of
level rate steers
----------------------------------------------------------------
% of diet steers/acre no.
0 1.00 8
25 1.25 10
50 1.50 12
75 1.75 14
----------------------------------------------------------------
Figure 1. Schematic outline of one replication of beef-finishing pastures.
Within each treatment, individual paddocks were gridded
into 900 ft2 blocks for pasture sampling purposed. Prior to
the allocation of a new grazing strip, one 2.7 ft2 quadrat was
cut from each grid block in that pasture allocation strip.
Samples were oven dried and CP, ADF, and neutral detergent
fiber (NDF) were determined using near infra-red reflectance
spectroscopy. Forage samples were collected from May 16 to
October 18, 1995. Species composition data were collected
from these paddocks as well. Forage dry matter intake (DMI)
was calculated by the difference method using quadrats clipped
prior to and immediately following grazing of an individual
paddock.
Results and Discussion: Forage quality of these cool-season
grass-legume pastures increased during the season, with CP
increasing and ADF decreasing. Crude protein was not limiting
for the animals at any time during the grazing season. Crude
protein requirement for medium-framed 700-pound steers gaining
2.0 lb/day is approximately 10%, according to the National
Research Council (1984). Crude protein levels of the forage
exceeded this requirement throughout the season (Fig. 2).
This result is in concurrence with the claims of Blaser et al.
(1977) that protein would not limit performance on cool-season
pastures. Linear regression was used to determine trend in
forage quality through the season using day of year as the
independent variable. For CP the relationship of CP to day of
year was significant (P=.05) for the 0%- and the 75%- grain
groups and a strong trend held true for the 25% and 50% groups
(P<.10). For ADF the relationship to day of year was also
significant (P=.05) for the 0%- and 75%- grain levels, and
again the strong trend held true for the 25% and 50% groups.
Cool-season pastures are often cited as being low quality
during the summer months. Results of this research indicate
that cool-season pastures managed to maintain vegetative
forage are quite high quality even through the summer months.
Forage dry matter availability also increased during the
season. Accurate forage sampling was hampered in the early
part of the season due to extremely wet weather so forage
availability data is presented for only Phase II. Forage
intake by grazing animals during the Phase I period also
appeared to be depressed due to heat stress and excessive
rainfall. Rainfall during the Phase I period was 18 in. above
normal for the research location. Phase II forage
availability at turn-in and daily forage intake are in Table
1. The observed intake indicates that the steers in the 0
grain treatment were consuming adequate forage dry matter to
maintain the expected ADG of 2.0 pounds per day.
A concern about feeding high levels of grain on pasture
is the substitution of grain intake for forage intake. Based
on the intake data in Table 2, it appears that the first
increment of grain fed has the greatest negative impact on
forage intake. The substitution coefficients for 25-, 50-,
and 75%-grain feeding levels were 1.26, 1.00, and .74,
respectively. Steer performance in this study as reported by
Martz et al. (1996) indicates very little difference in ADG
between the 0- and 25%-grain groups. The lacck of response to
grain supplementation at the 25% level may be the result of
decreased forage intake in the presence of added grain in a
quantity that was high enough to affect rumen performance but
not high enough to increase ADG. Average forage availability
was very similar between the 0- and 25%-grain supplemented
pastures, suggesting that forage availability was probably not
limiting intake. Mean forage availability in the 50- and 75%-
grain supplemented pastures was significantly lower than the
0 and 25% grain pastures. As the steers receiving higher
levels of supplementation increased body weight, their forage
consumption in terms of pounds of dry matter per head likely
increased more rapidly than the steers growing at a slower
rate. More forage was, therefore, consumed in each grazing
cycle and the residual following grazing was reduced. The
lower residual dry matter resulted in slower regrowth and
lower dry matter yield at turn-in on each subsequent grazing
cycle. The availability was low enough that forage intake may
have been limited on these pastures explaining why steer
performance on the 75%-grain pastures was not as high as what
would have been predicted.
In summary, forage quality tended to increase throughout
the grazing season on all treatments. Forage availability at
the beginning of each rotation remained near constant or
slightly increased for the 0- and 25%-grain groups while
availability tended to decrease slightly through the season
for the steers receiving 50 and 75% grain levels. It appears
that forage availability was more likely to limit steer
performance than would forage quality on these mixed cool-
season grass-legume pastures.
Literature Cited:
Blaser, R.E., W.C. Stringer, E.B. Rayburn, J.P. Fontenot, R.C.
Hammes, Jr., and H.T. Bryant. 1977. Forage-Fed Beef,
Production and Marketing Alternatives in the South. Southern
Cooperative Series, Bull. 220.
Martz, F.A., J.R. Gerrish, and V.G. Tate. 1996. Performance
of steers finished on pasture with four levels of grain
supplementation. IN: M.J. Williams (Ed.) Proc. Amer. Forage Grassl.
Council, Vol. 5. June 13-16, 1996, Vancouver, B.C., Canada. AFGC,
Georgetown, TX. (In Press)
National Research Council (NRC). 1984. Nutrient requirements
of beef cattle, sixth revised edition. National Research
Council, National Academy Press, Washington, D.C.
Table 2. Forage dry matter availability and voluntary
dry matter intake of steers grazing pasture at four
levels of grain supplementation.
============================================================
Grain Available Voluntary
supplementation dry matter forage
level at turn-in intake
____________________________________________________________
% of diet -- lb/A -- - lb/hd/day -
0 2659 21.5
25 2583 12.7
50 1983 9.6
75 2161 8.2
_____________________________________________________________
Figure 2. Trend in forage acid detergent fiber (ADF) and crude protein
(CP) in cool-season, grass-legume pastures across the grazing season.
---------------
1Research Assistant Professor, Research Professor of
Animal Sciences and Superintendent, and Research Associate,
respectively; University of Missouri-Forage Systems Research
Center (FSRC), Route 1 Box 80, Linneus, MO 64653
|
