Nebraska Sandhills upland range pastures were used to measure the effectsof stocking rate on forage nutrient content in early summer pastures. Stocked pastures had lower CP, in vitroorganic matter digestibility, forage availability, and higher NDF compared with ungrazed pastures. Clipped samples of current year growth had greater CP and in vitro organic matter digestibility than diet samples. Observed results indicate early season grazing decreasesdiet nutrient content and forage availability compared with ungrazed pastures, suggesting that cattle were consuming both current and previous year growth

Jenkins, K. H.

Judy, Jared V.

Klopfenstein, Terry J.

Musgrave, Jacki A.

Stalker, L. Aaron, Stalker

English

UNL | Libraries

University of Nebraska - Lincoln
DigitalCommons@University of Nebraska - Lincoln
Nebraska Beef Cattle Reports Animal Science Department
2015
Stocking Rate Effects on Forage Nutrient
Composition in Early Summer Pastures
Jared V. Judy
University of Nebraska-Lincoln, jjudy2@unl.edu
Jacki A. Musgrave
University of Nebraska-Lincoln, jmusgrave1@unl.edu
L. Aaron Stalker Stalker
University of Nebraska-Lincoln, stalkera@byui.edu
K. H. Jenkins
University of Nebraska-Lincoln, kjenkins2@unl.edu
Terry J. Klopfenstein
University of Nebraska-Lincoln, tklopfenstein1@unl.edu
Follow this and additional works at: http://digitalcommons.unl.edu/animalscinbcr
Part of the Large or Food Animal and Equine Medicine Commons, Meat Science Commons, and
the Veterinary Preventive Medicine, Epidemiology, and Public Health Commons
This Article is brought to you for free and open access by the Animal Science Department at DigitalCommons@University of Nebraska - Lincoln. It has
been accepted for inclusion in Nebraska Beef Cattle Reports by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln.
Judy, Jared V.; Musgrave, Jacki A.; Stalker, L. Aaron Stalker; Jenkins, K. H.; and Klopfenstein, Terry J., "Stocking Rate Effects on Forage
Nutrient Composition in Early Summer Pastures" (2015). Nebraska Beef Cattle Reports. 827.
http://digitalcommons.unl.edu/animalscinbcr/827
Page 48 — 2015 Nebraska Beef Cattle Report  © The Board of Regents of the University of Nebraska.  All rights reserved.
Stocking Rate Effects on Forage Nutrient Composition in 
Early Summer Pastures
Jared V. Judy
Jacki A. Musgrave
L. Aaron Stalker
Karla H. Jenkins
Terry J. Klopfenstein1
Summary
 Nebraska Sandhills upland range 
pastures were used to measure the 
effects of stocking rate on forage nutri-
ent content in early summer pastures. 
Stocked pastures had lower CP, in 
vitro organic matter digestibility, 
forage availability, and higher NDF 
compared with ungrazed pastures. 
Clipped samples of current year growth 
had greater CP and in vitro organic 
matter digestibility than diet samples. 
Observed results indicate early season 
grazing decreases diet nutrient content 
and forage availability compared with 
ungrazed pastures, suggesting that 
cattle were consuming both current and 
previous year growth. 
Introduction
Upland range in the Nebraska 
Sandhills is an excellent resource for 
grazing cattle. Native upland range 
is dominated by warm-season grass 
species. Forage quality increases dur-
ing the spring, reaching a peak during 
June, then steadily declines in qual-
ity throughout the remainder of the 
growing season (1997 Nebraska Beef 
Cattle Report, pp. 3-5). Research has 
shown changes in forage nutrient 
composition throughout the year but 
effects of stocking rate on Sandhills 
upland range were not addressed 
well. Therefore, the objectives of this 
research were to determine the effects 
of stocking rate on diet nutrient quali-
ty in early summer pasture, determine 
if new growth or previous year growth 
is being consumed, and determine 
forage production in the Nebraska 
Sandhills.
Table 1. Nutrient content of diet samples collected from esophageally fistulated cows comparing 
collection dates by stocking rate.
Item
Date
SEM1
P-value
5/18/2013 5/25/2013 6/1/2013 6/8/2013 Linear Quadratic Cubic
IVOMD
 Control2
 Light3
 Heavy4
70.3c
73.2a
71.2a
76.1b
65.1b
63.2b
79.8a
67.4c
62.5b
78.8a
66.2bc
63.2b
1.27
1.27
1.27
0.02
0.02
0.02
< 0.01
< 0.01
< 0.01
0.38
< 0.01
0.27
CP
 Control2
 Light3
 Heavy4
16.2b
17.1a
15.7a
20.5a
10.5b
8.9c
20.5a
11.1b
8.8c
18.9a
11.6b
10.8b
1.19
1.19
1.19
< 0.01
< 0.01
< 0.01
< 0.01
< 0.01
< 0.01
0.50
0.01
0.01
NDF
 Control2
 Light3
 Heavy4
54.4a
61.2b
68.8b
57.9a
78.1a
78.3a
45.0b
74.5a
69.9b
42.7b
73.2a
76.7a
3.44
3.44
3.44
< 0.01
< 0.01
0.08
0.35
< 0.01
0.48
0.06
0.01
< 0.01
1Standard error of the least squares mean.
2Non-stocked paddock (0 AUM/ac).
3Light stocking rate paddock (0.22 AUM/ac).
4Heavy stocking rate paddock (0.33 AUM/ac).
a-cMeans within rows lacking common superscript differ (P < 0.05).
Procedure
Twelve, five-acre upland range pad-
docks at the Gudmundsen Sandhills 
Laboratory near Whitman, Neb., 
were used. Paddocks were stocked 
at 0 (control), 0.22 (light), and 0.33 
(heavy) animal unit months per acre 
resulting in four replications per treat-
ment. A stocking rate of 0.60 AUM/
ac is commonly allotted for the entire 
year, so early in the growing season, 
before the majority of the growth 
has occurred, a stocking rate of 0.33 
AUM/ac was considered heavy. Each 
stocked paddock was continuously 
grazed and all paddocks were sampled 
weekly during the three week trial in 
2013 with the introduction of cattle 
on May 18 and the removal of cattle 
on June 8. Ten, 0.25 m2 quadrats per 
paddock were clipped at ground level 
on each sampling date and separated 
into previous year growth and current 
year growth. Three esophageally fis-
tulated cows were used to sample each 
pasture on each date to determine for-
age quality. Prior to each diet sample 
collection, cows were withheld from 
feed, but not water, for 12 hours, then 
transported to pastures where diets 
were to be collected. Cows were fitted 
with solid bottom bags after removal 
of the esophageal plug and introduced 
to the pasture, then allowed to graze 
for about 20 minutes. 
Samples were separated into a 
liquid and fibrous portion for lab 
analysis. Immediately after separa-
tion, diet samples were frozen and 
stored at -20°C, then lyophilized. 
Clipped samples were dried in a 
forced air oven at 60°C for 48 hours. 
Both diet and clipped samples were 
ground to pass a 1-mm screen in a 
Wiley mill. Samples were analyzed 
for nitrogen, NDF content using the 
Van Soest et al., (1991) method, and 
in vitro dry matter disappearance 
using the Tilley and Terry method 
with the modification of adding 1 g 
of urea to the buffer then adjusted to 
in vivo values (IVOMD). Results were 
analyzed using repeated measures in 
PROC GLIMMIX procedure of SAS 
(SAS Institute, Inc., Cary, N.C.) with 
paddock being the experimental unit. 
© The Board of Regents of the University of Nebraska.  All rights reserved. 2015 Nebraska Beef Cattle Report  — Page 49 
collected in control stocking rate 
paddocks had greater IVOMD  
(P < 0.05) compared with those 
collected in light and heavy stocking 
rate paddocks on collection dates 2, 3, 
and 4 (Table 3). Diet samples collected 
in light stocking rate paddocks had 
greater IVOMD (P < 0.05) than heavy 
stocking rate on June 1. Diet samples 
collected in control stocking rate 
paddocks had greater CP (P < 0.05) 
than light and heavy stocking rates 
on dates 2, 3, and 4. Light and heavy 
stocking rates showed no difference 
in CP (P > 0.05) for each sampling 
date. Diet samples collected from 
control stocking rate paddocks had 
lower NDF (P < 0.05) than light and 
heavy stocking rates on dates 2, 3, and 
4. These data suggest that stocking 
rate has a significant effect on the 
quality of the diet, helping to explain 
the treatment x date interaction 
in diet quality that was observed. 
When cattle were introduced into 
the paddock, they were able to select 
a diet greater in quality. As the 
grazing season progressed, cattle in 
the stocked paddocks consumed a 
diet lower in quality than the control 
paddocks, indicating that previous 
year growth was being consumed. 
Control stocking rate paddocks 
did reach a peak in diet quality 
in early June and then decreased 
in diet quality, likely due to plant 
maturation, which is in agreement 
with previous work (1997 Nebraska 
Beef Cattle Report, pp. 3-5).
For the clipped samples, no dif-
ferences occurred for previous year 
growth for CP, NDF, and IVOMD 
among treatments (P > 0.05) with 
overall means of 5.2%, 82.0%, and 
50.8%, respectively. Current year 
growth did not differ among treat-
ments for CP, NDF, and IVOMD  
(P > 0.05) with overall means of 
17.4%, 71.7, and 68.7%, respectively. 
However, CP (P < 0.01) and IVOMD 
(P < 0.02) content of current year 
growth increased linearly as stocking 
rate increased. Current growth  
was greater in CP and IVOMD  
(P < 0.01; Table 4) than diet sample 
and previous year growth on all dates. 
(Continued on next page)
Table 2. Nutrient content of clipped sample current year growth comparing collection dates by 
treatment.
Item
Date
SEM1
P-value
5/18/2013 5/25/2013 6/1/2013 6/8/2013 Linear Quadratic Cubic
IVOMD
 Control2
 Light3
 Heavy4
71.5b
69.3b
72.2
77.3a
74.5a
72.8
73.2b
75.3a
73.2
76.6ab
76.6a
74.8
2.74
2.74
2.74
0.03
0.03
0.03
0.30
0.30
0.30
0.03
0.03
0.03
CP
 Control2
 Light3
 Heavy4
19.2a
19.5ac
19.7a
17.6a
18.8a
17.7ab
16.7a
16.4b
17.0b
14.0b
16.4bc
15.6b
1.49
1.49
1.49
 < 0.01
 < 0.01
 < 0.01
0.90
0.90
0.90
0.86
0.86
0.86
NDF
 Control2
 Light3
 Heavy4
76.1
81.1
78.5
71.7
86.1
81.6
73.4
84.2
80.7
66.4
80.3
81.3
4.50
4.50
4.50
0.43
0.43
0.43
0.20
0.20
0.20
0.74
0.74
0.74
1Standard error of the least squares mean.
2Non-stocked paddock (0 AUM/ac).
3Light stocking rate paddock ( 0.22 AUM/ac).
4Heavy stocking rate paddock (0.33 AUM/ac).
a-cMeans within rows lacking common superscript differ (P < 0.05).
Table 3. Nutrient content of diet samples from esophageally fistulated cows comparing stocking 
rate on each date.
Item Control1 Light2 Heavy3 SEM4 P-value
IVOMD
 5/18/2013
 5/25/2013
 6/1/2013
 6/8/2013
70.3
76.1a
79.8a
78.8a
73.2
65.1b
67.4b
66.2b
71.2
63.2b
62.5c
63.2b
1.88
1.88
1.88
1.88
 0.12
< 0.01
< 0.01
< 0.01
CP
 5/18/2013
 5/25/2013
 6/1/2013
 6/8/2013
16.2
20.5a
20.5a
18.9a
17.1
10.5b
11.1b
11.6b
15.7
8.9b
8.8b
10.8b
2.08
2.08
2.08
2.08
0.50
< 0.01
< 0.01
< 0.01
NDF
 5/18/2013
 5/25/2013
 6/1/2013
 6/8/2013
54.4a
57.9b
45.0b
42.7b
61.2ab
78.1a
74.5a
73.2a
68.8b
78.3a
69.9a
76.7a
4.24
4.24
4.24
4.24
< 0.01
< 0.01
< 0.01
< 0.01
1Non-stocked paddock (0 AUM/ac).
2Light stocking rate paddock (0.22 AUM/ac).
3Heavy stocking rate paddock (0.33 AUM/ac).
4Standard error of the least squares mean.
a-cMeans within rows lacking common superscript differ (P < 0.05).
Results
Diet samples had significant 
treatment x date interactions  
(P < 0.01; Table 1) for CP, NDF, and 
IVOMD.  A quadratic effect was 
observed (P < 0.01) for diet IVOMD 
for control and heavy treatments 
with a cubic effect (P < 0.01) for the 
light stocking rate. Diet CP increased 
quadratically (P < 0.01) for the control 
treatment and showed a cubic effect  
(P < 0.01) for light and heavy 
treatments. Dietary NDF decreased 
linearly (P < 0.01) for control 
treatment and showed a cubic effect  
(P < 0.01) for light and heavy 
treatments. However, there were no 
treatment x date interactions  
(P > 0.05) in clipped samples. Clipped 
samples CP content decreased linearly 
(P < 0.05; Table 2) across all dates 
for each treatment and a cubic effect 
was shown for IVOMD (P < 0.05) 
of current year growth across all 
dates for all treatments. Diet samples 
Page 50 — 2015 Nebraska Beef Cattle Report  © The Board of Regents of the University of Nebraska.  All rights reserved.
Table 4.  Nutrient content of esophageal diet sample versus live and dead clipped samples.
Item Diet1 Live2 Dead3 SEM4 P-value
IVOMD
 5/18/2013
 5/25/2013
 6/1/2013
 6/8/2013
70.4a
66.5b
69.1b
68.4b
71.0a
74.8a
73.9a
76.0a
50.3b
53.2c
49.7c
49.6c
1.07
1.99
2.17
2.38
< 0.01
< 0.01
< 0.01
< 0.01
CP
 5/18/2013
 5/25/2013
 6/1/2013
 6/8/2013
16.1b
13.5b
13.6b
13.8b
21.0a
18.4a
16.8a
15.7a
6.9c
5.4c
5.5c
5.2c
1.12
1.54
1.48
1.64
< 0.01
< 0.01
< 0.01
< 0.01
NDF
 5/18/2013
 5/25/2013
 6/1/2013
 6/8/2013
59.4b
77.4
63.2b
64.6c
78.6a
79.8
79.4a
76.0b
82.9a
78.7
83.3a
83.0a
3.18
3.06
4.81
6.02
< 0.01
0.62
< 0.01
< 0.01
1Mean diet collection for all treatments using esophageally fistulated cows. 
2Mean clipped sample for all treatments current year forage growth.
3Mean clipped sample for all treatments for previous year forage growth. 
4Standard error of the least squares mean.
a-cMeans within rows lacking common superscript differ (P < 0.05).
Table 5. Nebraska Sandhills upland range forage availability comparing collection date by 
treatment. 
Item
 Date
SEM1
P-value
5/18/2013 5/25/2013 6/1/2013 6/8/2013 Linear Quadratic Cubic
Current year forage availability, lb/ac
 Control2
 Light3
 Heavy4
46.4d
28.6b
39.3
84.5c
24.4b
42.6
149.3b
49.7a
58.3
202.1a
52.3a
42.4
14.18
14.18
14.18
< 0.01
< 0.01
< 0.01
0.94
0.94
0.94
0.05
0.05
0.05
Previous year forage availability, lb/ac
 Control2
 Light3
 Heavy4
1087.1a
809.5a
907.8a
599.8b
236.9b
556.7b
533.5b
547.1a
440.9bc
440.9b
181.5b
303.6c
191.80
191.80
191.80
< 0.01
< 0.01
< 0.01
0.03
0.03
0.03
0.01
0.01
0.01
1Standard error of the least squares mean.
2Non-stocked paddock (0 AUM/ac).
3Light stocking rate paddock ( 0.22 AUM/ac).
4Heavy stocking rate paddock (0.33 AUM/ac).
a-cMeans within rows lacking common superscript differ (P < 0.05) .
Table 6. Nebraska Sandhills upland range forage availability comparing treatment by date.
Date Control2 Light3 Heavy4 SEM1 P-value
Current year forage availability, lb/ac
 5/18/2013
 5/25/2013
 6/1/2013
 6/8/2013
46.4
84.5a
149.3a
202.1a
28.6
24.4b
49.7b
52.3b
39.3
42.6b
58.3b
42.4b
19.23
19.23
19.23
19.23
0.24
< 0.01
< 0.01
< 0.01
Previous year forage availability, lb/ac
 5/18/2013
 5/25/2013
 6/1/2013
 6/8/2013
1087.1
599.8a
533.5
440.9
809.5
236.9b
547.1
181.5
907.8
556.7a
440.9
303.6
224.21
224.21
224.21
224.21
0.23
< 0.01
0.23
0.23
1 Standard error of the least squares mean
2 Non-stocked paddock (0 AUM/ac)
3 Light stocking rate paddock ( 0.22 AUM/ac)
4 Heavy stocking rate paddock (0.33 AUM/ac)
 a-cMeans within rows lacking common superscript differ (P < 0.05) 
Neutral detergent fiber was greater  
(P < 0.01) in clipped samples versus 
diet samples. These results occur 
because cattle are selective and there 
are differences between collec-
tion methods. Current year growth 
increased linearly for all treatments  
(P < 0.01; Table 5). Control pad-
docks had greater current year forage 
availability versus stocked pastures 
(P < 0.01; Table 6) for all but the first 
sampling date. Stocking rate affects 
forage quality and, therefore, diet 
quality in early summer as well as for-
age availability. 
The NRC model was used in a 
hypothetical example to compare per-
formance of cows consuming either 
the control pasture or heavily stocked 
pasture. A 1,200 lb March calving 
cow producing 25 lb of milk at peak 
lactation, consuming an estimated 
2.4% of her body weight was used in 
the analysis. Diet quality from control 
pastures exceeded both energy and 
protein requirements of the animal. 
However, heavily grazed pastures 
had much lower diet quality, which 
resulted in both a negative energy 
and protein balance by the end of the 
second week in the pasture. By the 
final sampling date which occurred 
after three weeks of grazing, the qual-
ity of the diet increased for the heavy 
stocked pasture which resulted in the 
animals maintaining body condition. 
Cattle grazing upland range early in 
the growing season initially consume 
diets high in quality but as pastures 
are grazed, diet quality decreases. 
Hence, producers trying to graze 
upland range early in the growing 
season need to understand the effects 
of grazing on diet quality and manage 
accordingly by rotating through pas-
tures more frequently or delaying the 
start of grazing. 
 
1Jared V. Judy, graduate student; Jacki A. 
Musgrave, research technician; L. Aaron Stalker, 
associate professor, University of Nebraska–
Lincoln (UNL) West Central Research and 
Extension Center, North Platte, Neb.; Karla H. 
Jenkins, assistant professor; UNL Panhandle 
Research and Extension Center, Scottsbluff, 
Neb.; Terry J. Klopfenstein, professor, UNL 
Department of Animal Science, Lincoln, Neb.


Stocking Rate Effects on Forage Nutrient Composition in Early Summer Pastures

DigitalCommons@University of Nebraska

University of Nebraska - LincolnDigitalCommons@University of Nebraska - LincolnNebraska Beef Cattle Reports Animal Science Department2015Stocking Rate Effects on Forage NutrientComposition in Early Summer PasturesJared V. JudyUniversity of Nebraska-Lincoln, jjudy2@unl.eduJacki A. MusgraveUniversity of Nebraska-Lincoln, jmusgrave1@unl.eduL. Aaron Stalker StalkerUniversity of Nebraska-Lincoln, stalkera@byui.eduK. H. JenkinsUniversity of Nebraska-Lincoln, kjenkins2@unl.eduTerry J. KlopfensteinUniversity of Nebraska-Lincoln, tklopfenstein1@unl.eduFollow this and additional works at: http://digitalcommons.unl.edu/animalscinbcrPart of the Large or Food Animal and Equine Medicine Commons, Meat Science Commons, andthe Veterinary Preventive Medicine, Epidemiology, and Public Health CommonsThis Article is brought to you for free and open access by the Animal Science Department at DigitalCommons@University of Nebraska - Lincoln. It hasbeen accepted for inclusion in Nebraska Beef Cattle Reports by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln.Judy, Jared V.; Musgrave, Jacki A.; Stalker, L. Aaron Stalker; Jenkins, K. H.; and Klopfenstein, Terry J., "Stocking Rate Effects on ForageNutrient Composition in Early Summer Pastures" (2015). Nebraska Beef Cattle Reports. 827.http://digitalcommons.unl.edu/animalscinbcr/827Page 48 — 2015 Nebraska Beef Cattle Report  © The Board of Regents of the University of Nebraska.  All rights reserved.Stocking Rate Effects on Forage Nutrient Composition in Early Summer PasturesJared V. JudyJacki A. MusgraveL. Aaron StalkerKarla H. JenkinsTerry J. Klopfenstein1Summary Nebraska Sandhills upland range pastures were used to measure the effects of stocking rate on forage nutri-ent content in early summer pastures. Stocked pastures had lower CP, in vitro organic matter digestibility, forage availability, and higher NDF compared with ungrazed pastures. Clipped samples of current year growth had greater CP and in vitro organic matter digestibility than diet samples. Observed results indicate early season grazing decreases diet nutrient content and forage availability compared with ungrazed pastures, suggesting that cattle were consuming both current and previous year growth. IntroductionUpland range in the Nebraska Sandhills is an excellent resource for grazing cattle. Native upland range is dominated by warm-season grass species. Forage quality increases dur-ing the spring, reaching a peak during June, then steadily declines in qual-ity throughout the remainder of the growing season (1997 Nebraska Beef Cattle Report, pp. 3-5). Research has shown changes in forage nutrient composition throughout the year but effects of stocking rate on Sandhills upland range were not addressed well. Therefore, the objectives of this research were to determine the effects of stocking rate on diet nutrient quali-ty in early summer pasture, determine if new growth or previous year growth is being consumed, and determine forage production in the Nebraska Sandhills.Table 1. Nutrient content of diet samples collected from esophageally fistulated cows comparing collection dates by stocking rate.ItemDateSEM1P-value5/18/2013 5/25/2013 6/1/2013 6/8/2013 Linear Quadratic CubicIVOMD Control2 Light3 Heavy470.3c73.2a71.2a76.1b65.1b63.2b79.8a67.4c62.5b78.8a66.2bc63.2b1.271.271.270.020.020.02< 0.01< 0.01< 0.010.38< 0.010.27CP Control2 Light3 Heavy416.2b17.1a15.7a20.5a10.5b8.9c20.5a11.1b8.8c18.9a11.6b10.8b1.191.191.19< 0.01< 0.01< 0.01< 0.01< 0.01< 0.010.500.010.01NDF Control2 Light3 Heavy454.4a61.2b68.8b57.9a78.1a78.3a45.0b74.5a69.9b42.7b73.2a76.7a3.443.443.44< 0.01< 0.010.080.35< 0.010.480.060.01< 0.011Standard error of the least squares mean.2Non-stocked paddock (0 AUM/ac).3Light stocking rate paddock (0.22 AUM/ac).4Heavy stocking rate paddock (0.33 AUM/ac).a-cMeans within rows lacking common superscript differ (P < 0.05).ProcedureTwelve, five-acre upland range pad-docks at the Gudmundsen Sandhills Laboratory near Whitman, Neb., were used. Paddocks were stocked at 0 (control), 0.22 (light), and 0.33 (heavy) animal unit months per acre resulting in four replications per treat-ment. A stocking rate of 0.60 AUM/ac is commonly allotted for the entire year, so early in the growing season, before the majority of the growth has occurred, a stocking rate of 0.33 AUM/ac was considered heavy. Each stocked paddock was continuously grazed and all paddocks were sampled weekly during the three week trial in 2013 with the introduction of cattle on May 18 and the removal of cattle on June 8. Ten, 0.25 m2 quadrats per paddock were clipped at ground level on each sampling date and separated into previous year growth and current year growth. Three esophageally fis-tulated cows were used to sample each pasture on each date to determine for-age quality. Prior to each diet sample collection, cows were withheld from feed, but not water, for 12 hours, then transported to pastures where diets were to be collected. Cows were fitted with solid bottom bags after removal of the esophageal plug and introduced to the pasture, then allowed to graze for about 20 minutes. Samples were separated into a liquid and fibrous portion for lab analysis. Immediately after separa-tion, diet samples were frozen and stored at -20°C, then lyophilized. Clipped samples were dried in a forced air oven at 60°C for 48 hours. Both diet and clipped samples were ground to pass a 1-mm screen in a Wiley mill. Samples were analyzed for nitrogen, NDF content using the Van Soest et al., (1991) method, and in vitro dry matter disappearance using the Tilley and Terry method with the modification of adding 1 g of urea to the buffer then adjusted to in vivo values (IVOMD). Results were analyzed using repeated measures in PROC GLIMMIX procedure of SAS (SAS Institute, Inc., Cary, N.C.) with paddock being the experimental unit. © The Board of Regents of the University of Nebraska.  All rights reserved. 2015 Nebraska Beef Cattle Report  — Page 49 collected in control stocking rate paddocks had greater IVOMD  (P < 0.05) compared with those collected in light and heavy stocking rate paddocks on collection dates 2, 3, and 4 (Table 3). Diet samples collected in light stocking rate paddocks had greater IVOMD (P < 0.05) than heavy stocking rate on June 1. Diet samples collected in control stocking rate paddocks had greater CP (P < 0.05) than light and heavy stocking rates on dates 2, 3, and 4. Light and heavy stocking rates showed no difference in CP (P > 0.05) for each sampling date. Diet samples collected from control stocking rate paddocks had lower NDF (P < 0.05) than light and heavy stocking rates on dates 2, 3, and 4. These data suggest that stocking rate has a significant effect on the quality of the diet, helping to explain the treatment x date interaction in diet quality that was observed. When cattle were introduced into the paddock, they were able to select a diet greater in quality. As the grazing season progressed, cattle in the stocked paddocks consumed a diet lower in quality than the control paddocks, indicating that previous year growth was being consumed. Control stocking rate paddocks did reach a peak in diet quality in early June and then decreased in diet quality, likely due to plant maturation, which is in agreement with previous work (1997 Nebraska Beef Cattle Report, pp. 3-5).For the clipped samples, no dif-ferences occurred for previous year growth for CP, NDF, and IVOMD among treatments (P > 0.05) with overall means of 5.2%, 82.0%, and 50.8%, respectively. Current year growth did not differ among treat-ments for CP, NDF, and IVOMD  (P > 0.05) with overall means of 17.4%, 71.7, and 68.7%, respectively. However, CP (P < 0.01) and IVOMD (P < 0.02) content of current year growth increased linearly as stocking rate increased. Current growth  was greater in CP and IVOMD  (P < 0.01; Table 4) than diet sample and previous year growth on all dates. (Continued on next page)Table 2. Nutrient content of clipped sample current year growth comparing collection dates by treatment.ItemDateSEM1P-value5/18/2013 5/25/2013 6/1/2013 6/8/2013 Linear Quadratic CubicIVOMD Control2 Light3 Heavy471.5b69.3b72.277.3a74.5a72.873.2b75.3a73.276.6ab76.6a74.82.742.742.740.030.030.030.300.300.300.030.030.03CP Control2 Light3 Heavy419.2a19.5ac19.7a17.6a18.8a17.7ab16.7a16.4b17.0b14.0b16.4bc15.6b1.491.491.49 < 0.01 < 0.01 < 0.010.900.900.900.860.860.86NDF Control2 Light3 Heavy476.181.178.571.786.181.673.484.280.766.480.381.34.504.504.500.430.430.430.200.200.200.740.740.741Standard error of the least squares mean.2Non-stocked paddock (0 AUM/ac).3Light stocking rate paddock ( 0.22 AUM/ac).4Heavy stocking rate paddock (0.33 AUM/ac).a-cMeans within rows lacking common superscript differ (P < 0.05).Table 3. Nutrient content of diet samples from esophageally fistulated cows comparing stocking rate on each date.Item Control1 Light2 Heavy3 SEM4 P-valueIVOMD 5/18/2013 5/25/2013 6/1/2013 6/8/201370.376.1a79.8a78.8a73.265.1b67.4b66.2b71.263.2b62.5c63.2b1.881.881.881.88 0.12< 0.01< 0.01< 0.01CP 5/18/2013 5/25/2013 6/1/2013 6/8/201316.220.5a20.5a18.9a17.110.5b11.1b11.6b15.78.9b8.8b10.8b2.082.082.082.080.50< 0.01< 0.01< 0.01NDF 5/18/2013 5/25/2013 6/1/2013 6/8/201354.4a57.9b45.0b42.7b61.2ab78.1a74.5a73.2a68.8b78.3a69.9a76.7a4.244.244.244.24< 0.01< 0.01< 0.01< 0.011Non-stocked paddock (0 AUM/ac).2Light stocking rate paddock (0.22 AUM/ac).3Heavy stocking rate paddock (0.33 AUM/ac).4Standard error of the least squares mean.a-cMeans within rows lacking common superscript differ (P < 0.05).ResultsDiet samples had significant treatment x date interactions  (P < 0.01; Table 1) for CP, NDF, and IVOMD.  A quadratic effect was observed (P < 0.01) for diet IVOMD for control and heavy treatments with a cubic effect (P < 0.01) for the light stocking rate. Diet CP increased quadratically (P < 0.01) for the control treatment and showed a cubic effect  (P < 0.01) for light and heavy treatments. Dietary NDF decreased linearly (P < 0.01) for control treatment and showed a cubic effect  (P < 0.01) for light and heavy treatments. However, there were no treatment x date interactions  (P > 0.05) in clipped samples. Clipped samples CP content decreased linearly (P < 0.05; Table 2) across all dates for each treatment and a cubic effect was shown for IVOMD (P < 0.05) of current year growth across all dates for all treatments. Diet samples Page 50 — 2015 Nebraska Beef Cattle Report  © The Board of Regents of the University of Nebraska.  All rights reserved.Table 4.  Nutrient content of esophageal diet sample versus live and dead clipped samples.Item Diet1 Live2 Dead3 SEM4 P-valueIVOMD 5/18/2013 5/25/2013 6/1/2013 6/8/201370.4a66.5b69.1b68.4b71.0a74.8a73.9a76.0a50.3b53.2c49.7c49.6c1.071.992.172.38< 0.01< 0.01< 0.01< 0.01CP 5/18/2013 5/25/2013 6/1/2013 6/8/201316.1b13.5b13.6b13.8b21.0a18.4a16.8a15.7a6.9c5.4c5.5c5.2c1.121.541.481.64< 0.01< 0.01< 0.01< 0.01NDF 5/18/2013 5/25/2013 6/1/2013 6/8/201359.4b77.463.2b64.6c78.6a79.879.4a76.0b82.9a78.783.3a83.0a3.183.064.816.02< 0.010.62< 0.01< 0.011Mean diet collection for all treatments using esophageally fistulated cows. 2Mean clipped sample for all treatments current year forage growth.3Mean clipped sample for all treatments for previous year forage growth. 4Standard error of the least squares mean.a-cMeans within rows lacking common superscript differ (P < 0.05).Table 5. Nebraska Sandhills upland range forage availability comparing collection date by treatment. Item DateSEM1P-value5/18/2013 5/25/2013 6/1/2013 6/8/2013 Linear Quadratic CubicCurrent year forage availability, lb/ac Control2 Light3 Heavy446.4d28.6b39.384.5c24.4b42.6149.3b49.7a58.3202.1a52.3a42.414.1814.1814.18< 0.01< 0.01< 0.010.940.940.940.050.050.05Previous year forage availability, lb/ac Control2 Light3 Heavy41087.1a809.5a907.8a599.8b236.9b556.7b533.5b547.1a440.9bc440.9b181.5b303.6c191.80191.80191.80< 0.01< 0.01< 0.010.030.030.030.010.010.011Standard error of the least squares mean.2Non-stocked paddock (0 AUM/ac).3Light stocking rate paddock ( 0.22 AUM/ac).4Heavy stocking rate paddock (0.33 AUM/ac).a-cMeans within rows lacking common superscript differ (P < 0.05) .Table 6. Nebraska Sandhills upland range forage availability comparing treatment by date.Date Control2 Light3 Heavy4 SEM1 P-valueCurrent year forage availability, lb/ac 5/18/2013 5/25/2013 6/1/2013 6/8/201346.484.5a149.3a202.1a28.624.4b49.7b52.3b39.342.6b58.3b42.4b19.2319.2319.2319.230.24< 0.01< 0.01< 0.01Previous year forage availability, lb/ac 5/18/2013 5/25/2013 6/1/2013 6/8/20131087.1599.8a533.5440.9809.5236.9b547.1181.5907.8556.7a440.9303.6224.21224.21224.21224.210.23< 0.010.230.231 Standard error of the least squares mean2 Non-stocked paddock (0 AUM/ac)3 Light stocking rate paddock ( 0.22 AUM/ac)4 Heavy stocking rate paddock (0.33 AUM/ac) a-cMeans within rows lacking common superscript differ (P < 0.05) Neutral detergent fiber was greater  (P < 0.01) in clipped samples versus diet samples. These results occur because cattle are selective and there are differences between collec-tion methods. Current year growth increased linearly for all treatments  (P < 0.01; Table 5). Control pad-docks had greater current year forage availability versus stocked pastures (P < 0.01; Table 6) for all but the first sampling date. Stocking rate affects forage quality and, therefore, diet quality in early summer as well as for-age availability. The NRC model was used in a hypothetical example to compare per-formance of cows consuming either the control pasture or heavily stocked pasture. A 1,200 lb March calving cow producing 25 lb of milk at peak lactation, consuming an estimated 2.4% of her body weight was used in the analysis. Diet quality from control pastures exceeded both energy and protein requirements of the animal. However, heavily grazed pastures had much lower diet quality, which resulted in both a negative energy and protein balance by the end of the second week in the pasture. By the final sampling date which occurred after three weeks of grazing, the qual-ity of the diet increased for the heavy stocked pasture which resulted in the animals maintaining body condition. Cattle grazing upland range early in the growing season initially consume diets high in quality but as pastures are grazed, diet quality decreases. Hence, producers trying to graze upland range early in the growing season need to understand the effects of grazing on diet quality and manage accordingly by rotating through pas-tures more frequently or delaying the start of grazing.  1Jared V. Judy, graduate student; Jacki A. Musgrave, research technician; L. Aaron Stalker, associate professor, University of Nebraska–Lincoln (UNL) West Central Research and Extension Center, North Platte, Neb.; Karla H. Jenkins, assistant professor; UNL Panhandle Research and Extension Center, Scottsbluff, Neb.; Terry J. Klopfenstein, professor, UNL Department of Animal Science, Lincoln, Neb.

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Stocking Rate Effects on Forage Nutrient Composition in Early Summer Pastures

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