REV103415

• Permit No: C1981071
• IBM Index Class Name: Revision
• Doc Date: 12/1/1987
• Doc Name: ARTICLEs 1)‎HERBAGE INTAKE RATES OF BEEF CATTLE 2)‎GRAZING ALFALFA
• Type & Sequence: TR17
• Media Type: D
• Archive: No

DOUGHERTI'ET AL.:BEEFCATTLE GRAZING ALFALFA LOOS
Table 4. Least squares means Igrand mesa plus direct effect) of variables associated with grazing (Exp. t)

Variable
Units
0 Treatment Ihl
1
2
SEi
Linear P~Value
Quadratic
I n[ake kg h' 2.96 1,88 1.56 0.22 0.00 0.05
Intake kg 1100 kg LWI" h' 0.76 0.49 0.41 0.06 0.00 0.05
Iliting rate bites min" 26.2 20.9 19.4 1.92 0.00 0.27
Bite sire g bite ' 1.96 1.54 1.3fi 2.07 O.OI 0.50
Bile size mg lkg LWt' S.17 407 3.fi0 O.Sd O.OI 0.50
RDhI bfg he" 1 50 2.OB 2.25 0.112 0.00 0.04
Utilization 90 51.1 31.9 26.5 3.7 0.00 0.04
Sward height cm 26.9 34.0 32.9 1.56 0.02 0.03
1 Standard error of difference
The ingestive behavior of heifers grazing in the sec-
ondand third hours of the grazing session occurred at
a considerably slower rate than heifers grazing in the
first hour (Table 4). The rate ofbiting and mean intake
per bite were both less than that measured in animals
in the first hour of grazing, with bite size being [he
more affected.
Experfrnenf /!. The alfalfa canopy grazed in the sec-
ond experiment was at ~0% (lowering, about 7 days
older, nearly 13 cm shorter, and had about one half
the herbage mass of the alfalfa used in Exp. 1 (Table
2). Plots, as determined by the length of tethers, were
the same area (20 m-) as used in Exp, I. Consequently,
heifers were offered about one half the herbage allow-
ance that they had had in the earlier study (Table 2).
In this experiment, differences between heifers and
between days were not significant, except for rate of
biling(Table 5). The direct effects were, however, highly
significant for variables describing the ingestive pro-
cess and the sward following grazing, except for mean
herbage intake per bite (Table 5). For these variables
there was very little carryover of the treatment that
the heifers had received the previous day, as seen in
the high P-values of F for the residual effect (Table 5).
As for data obtained in Exp. 1, only the least squares
estimates of means are presented for measured vari-
ables (Table 6). Regression analysis also detected strong
linear effects of grazing time within the grazing session
on variables describing the process oC grazing or the
status of the crop following grazing (Table 6). The
quadratic component contributed little [o the model
except for rate of biting (Table 6).
The rate of ingestion was highest during the first
hour of grazing and declined linearly with grazing time,
with the differences between the first and second hours
of grazing being larger than those between the second
and third hours of grazing (Table 6). Rates of biting
varied considerably with grazing time, with less dif-
(crence being observed between the second and third
hours. Herbage DM intake per bite did not vary sig-
nificantly with grazing time and averaged 1.17 g. Al-
falfa canopy height was diminished by 17, 12, and 8
cm during the first, second, and third hours of grazing,
respectively. Approximately 75°'0 of the available Dot
of the alfalfa sward was consumed in the first hour oC
grazing, with 46 and 37°'0 consumed in the second and
third hours, respectively', within the session. Grazing
reduced the herbage mass to less than 500 kg ha-'
during the first hour and to approximately 1000 kg
ha 'during the second and third hours ofgrazing.
The dlffcrences between experiments were largely
attributable to the differeltces in herbage mass, canopy
Table 5. Summery of analysis or variance for Exp. II

Variable
Units
Animal Source
Day Direct
Residual
P-value of F
Intake kg h" 0.16 0.07 0.00 0.24
Intake kg II00 kg LtYI" h-' 0.15 0.07 0.00 0.29
Biting rate bites min" 0.09 0.00 0.00 0.80
Rite sire g bile" 0.63 0.47 0.97 0.69
Bite size mg Ikg LWI" 0.55 0.48 0.96 O.fi5
RDA1 Alg ha" 0.11 0.34 0.00 0.17
Utilization % 0.10 019 0.00 0.17
Sward height cm 0.06 0.26 0.00 0.03
height, and herbage allowance (Table 2). The differ-
ences between heifers were considerable during Exp.
1 (Table 3) and slight during Exp. 11 (Table 5). Day-
to-day variation was also more pronounced during Exp.
1 (Tables 3 and ~). The weather during the two ex-
perimentswas similar (Table 7), and temperatures were
within the thermoneutral zone of beef cattle during
the morning grazing sessions (National Research
Council, 1984). The weatherduring Exp. 11 was slightly
cooler during the night and drier than that of Exp. I
(Table 7).
DISCUSSION
The use of the change-overdesign ofBerenblut (1964)
in conjunction with the tethered grazing technique per-
mitted separation of the differences between heifers
and between days from the effect of the grazing treat-
ment and the estimation ofthe magnitude ofthe carry-
over effect. The carry-over effects of the grazing treat-
ment of the previous day were not significant for the
measured variables ofingestive behavior and the sward
after grazing. The free-range grazing sessions of the
afternoon, and the long overnight fasts, may have min-
imized the carry-over effect of the grazing treatment,
if any existed.
Highest rates of DM ingestion approached 3 kg h-'
[0.7 kg (100 kg LW) h-') in Exp. l where the ar-
chitecture ofthe sward allowed heifers to harvest bites
of alfalfa averaging close to 2.0 g. These estimates of
herbage mass (DM) intake per bite are larger than those
usually reported for cattle of this class (Hodgson,
1982b); however, estimates of herbage intake per bite
approaching these values have been recorded for cattle
grazing perennial ryegrass (Lolium perenne L.) (Hodg-
son and Jamieson, 1981). Estimates of herbage intake
per bite obtained from six bolus extrusa samples (ap-
proximately ~0 bites) from slightly lighter, esopha-
geally fistulated steers grazing similar alfalfa at this