Mob stocking effects on herbage nutritive value, herbage accumulation, and plant species ...

136 Pages·2015·2.84 MB·English

by  Robert Bauer

Mob stocking effects on herbage nutritive value, herbage accumulation, and plant species
composition

Robert Benjamin Bauer

Thesis submitted to the faculty of the Virginia Polytechnic Institute and State University in
partial fulfillment of the requirements for the degree of

Master of Science
In
Crop and Soil Environmental Science

Benjamin F. Tracy
Mark A. McCann
John H. Fike

April 24, 2015
Blacksburg, Virginia

Keywords: Mob stocking, forage nutritive value, clover, esophageal cannulation
Mob stocking affects herbage nutritive value, herbage accumulation, clover cover, and diet
selected by beef cattle

Robert Benjamin Bauer

ABSTRACT

Mob stocking is a variation of rotational stocking known for restricting a large number of
animals to a small area before being moved to new grass after a few hours. This method allows a
long (90-day) recovery period but was hypothesized to diminish the nutritional value of herbage
relative to continuous and rotational stocking with lesser stocking density at similar stocking
rates. This thesis summarizes two studies conducted in Blacksburg and Raphine, and in Steeles
Tavern, VA, respectively, at a single beef cattle stocking rate of 12 animal unit months per
hectare live body weight. The objectives were to: (1) compare the yield and nutritional value of
herbage in pastures managed with three stocking methods, termed “mob”, “rotational”, and
“continuous” stocking; (2) compare the abundance of seeded clover species among the stocking
methods; and (3) estimate the nutritional value of herbage that is consumed by beef cattle during
ʻmobʼ stocking using extrusa sampled from esophageally-cannulated animals. Analysis of
standing herbage during two years produced several important findings. Although standing
herbage mass was significantly greater in mob stocked pastures at Blacksburg and Raphine,
aboveground net primary productivity in 2014 did not differ significantly among mob, rotational,
and continuous stocking at any of the project locations. Herbage nutritive value did not differ
significantly among stocking methods over two years at Blacksburg and Raphine; however,
herbage from mob stocked pastures at Steeles Tavern contained significantly greater
concentrations of crude protein in September and October relative to herbage from continuous-
and rotationally-stocked pastures at those times. Differences in herbage mass likely contributed
to significant differences in establishment of seeded clovers: red
clover [Trifolium pratense L. ‘Cinnamon Plus’] establishment was similar among stocking
methods but white clover [Trifolium repens L. ‘Will’] establishment was greater in continuously
stocked pastures than mob and rotationally stocked pastures. Hand-clipped samples collected at
Blacksburg in September 2014 significantly underestimated the crude protein content of the
herbage selected by the steers, although the concentrations of fiber constituents in herbage did
not differ significantly between clipped samples and esophageal samples. Although the nutritive
value of the herbage on offer did not generally differ among stocking methods at this stocking
rate, diet selected was at times less nutritious during mob stocking than continuous and rotational
stocking methods. At this stocking rate, stocking method had less influence on pastures than
seasonal variation in weather and plant maturity.

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ACKNOWLEDGEMENTS

This project was funded through grants from the United States Department of Agriculture
Conservation Innovation Grant (CIG) program and John Lee Pratt Animal Nutrition Program at
Virginia Tech.

I thank the Virginia Tech Department of Biological Systems Engineering for the use of the
pasture facilities at Prices Fork Research Center. Thank you to the Virginia Tech Beef Center for
use of beef cattle. Thank you to the staff of the Shenandoah Valley Agricultural Research and
Extension Center (SVAREC) for management and collection of forages and livestock.

My committee members: Ben Tracy, Mark McCann, and John Fike guided the experimental
design, fieldwork, data analysis, and thesis writing. Thank you for your support and advice.

Many Virginia Tech staff members, graduate students, and undergraduate students contributed to
this work, especially David Fiske, Amy Tanner, Laura Lehman, Joao Flores, Gordon Jones,
Fatou Fall, and Scott Neil. Thank you, all.

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TABLE OF CONTENTS

ABSTRACT .................................................................................................................................. II
ACKNOWLEDGEMENTS ....................................................................................................... IV
TABLE OF CONTENTS ............................................................................................................ V
LIST OF TABLES .................................................................................................................... VII
LIST OF FIGURES ................................................................................................................. VIII
LIST OF EQUATIONS .............................................................................................................. IX
ABBREVIATIONS ...................................................................................................................... X
CHAPTER 1. INTRODUCTION ................................................................................................ 1
1.1 BACKGROUND AND MOTIVATION ........................................................................................... 1
1.2 RESEARCH OBJECTIVES AND HYPOTHESES.............................................................................. 2
CHAPTER 2. LITERATURE REVIEW .................................................................................... 4
2.1 STOCKING METHODS .............................................................................................................. 4
2.1.1 Definition of grazing systems and stocking methods ..................................................... 4
2.1.2 Relationships between stocking methods and grazing systems ...................................... 6
2.1.3 Relationship between stocking methods and forage physiology .................................... 9
2.1.4 Forage accumulation response to stocking methods ................................................... 12
2.2 FORAGE NUTRITIVE VALUE RESPONSE TO STOCKING METHODS ............................................ 15
2.2.1 Definitions of forage nutritive value .......................................................................... 15
2.2.2 Effect of plant physiology on nutritive value of grazed forage .................................. 16
2.2.3 Forage nutritive value response to stocking methods ............................................... 19
2.3 LEGUME ESTABLISHMENT IN COOL-SEASON PASTURES ........................................................ 20
2.3.1 Role of legumes in pastures ......................................................................................... 20
2.3.2 Planting and persistence of red and white clovers ...................................................... 21
2.3.3 Legume establishment response to stocking methods .................................................. 23
2.3.4 Effect of legume establishment on forage nutritive value ............................................ 24
2.3 DIET SELECTION IN COOL-SEASON PASTURES ....................................................................... 25
2.3.1 Definition of diet selection, preference, and opportunity ............................................ 25
2.3.2 Patterns of diet selection .............................................................................................. 27
2.3.3 Effect of stocking methods on diet selection ................................................................ 28
CONCLUSION .............................................................................................................................. 31
REFERENCES .............................................................................................................................. 33
CHAPTER 3. MATERIALS AND METHODS ....................................................................... 48
3.1 STUDY SITES ........................................................................................................................ 48
3.1.1 Blacksburg and Raphine, VA ....................................................................................... 48
3.1.2 Steeles Tavern, VA ....................................................................................................... 49
3.2 EXPERIMENTAL DESIGN ........................................................................................................ 50
3.3 METHODS ............................................................................................................................. 51
3.3.1 Herbage mass............................................................................................................... 51
3.3.2 Herbage accumulation and disappearance ................................................................. 53
3.3.3 Plant species composition ............................................................................................ 55
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TABLE OF CONTENTS (continued)

3.3.4 Herbage nutritive value ............................................................................................... 56
3.3.5 Nutritive value of herbage selected by esophageally cannulated beef steers .............. 56
3.4 STATISTICAL ANALYSIS ........................................................................................................ 57
REFERENCES .............................................................................................................................. 60
CHAPTER 4. RESULTS, DISCUSSION, AND CONCLUSIONS ........................................ 73
4.1 Results ............................................................................................................................. 73
4.1.1 Herbage mass............................................................................................................... 73
4.1.2 Herbage accumulation and disappearance ................................................................. 75
4.1.3 Plant species composition ............................................................................................ 77
4.1.4 Herbage nutritive value ............................................................................................... 78
4.1.5 Nutritive value of herbage from esophageal cannula of beef steers ............................ 80
4.2 DISCUSSION ......................................................................................................................... 81
4.2.1 Herbage mass............................................................................................................... 81
4.2.2 Herbage accumulation and disappearance ................................................................. 86
4.2.3 Plant species composition ............................................................................................ 90
4.2.4 Herbage nutritive value ............................................................................................... 93
4.2.5 Nutritive value of herbage sampled from esophageal cannula of beef steers ............. 97
4.3 CONCLUSIONS .................................................................................................................... 100
REFERENCES ............................................................................................................................ 103

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LIST OF TABLES

Table 3.1: Mean soil pH, phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and
organic matter (OM) in April 2013 at Blacksburg, Raphine, and Steeles Tavern, VA. ....... 62
Table 3.2: Average monthly weather data between January 1 and December 31 for Blacksburg
and Raphine, VA† (2013-2014), obtained from NOAA (2014).. ......................................... 63
Table 3.3: Herd characteristics and stocking management for 11 April 2013—14 Nov. 2014 at
the Blacksburg and Raphine, VA locations. ......................................................................... 64
Table 3.4: Herd characteristics and stocking management 5 May—23 Dec. 2014 at the Steeles
Tavern, VA location.............................................................................................................. 65
Table 3.5: Dates of herbage sampling at Blacksburg and Raphine, VA in 2013-2014. ............... 66
Table 3.6: Dates of herbage sampling in 2014 at the Steeles Tavern, VA location. .................... 67
Table 4.1: Least squares means of standing herbage biomass at Steeles Tavern, VA from
May-Nov. 2014, averaged among stocking methods.......................................................... 107
Table 4.2: Least squares means of annual days of grazing at Blacksburg, Raphine, and Steeles
Tavern, VA by stocking method, averaged among years and pasture replicates. .............. 107
Table 4.3: Rising plate meter (RPM) coefficients for May-Nov. 2014. ..................................... 108
Table 4.4: Least squares means of rates of herbage accumulation at Blacksburg and Raphine, VA
during 5 May-8 Nov. 2014, averaged among locations and stocking methods. ................. 108
Table 4.5: Least squares means of rates of herbage accumulation at Steeles Tavern, VA during
22 July—22 Nov. 2014, averaged among stocking methods.............................................. 109
Table 4.6: Least squares means of percent cover of white clover, red clover, and bare ground by
stocking method at Blacksburg and Raphine, VA during 9 April 2013—8 Nov. 2014,
averaged among time and locations. ................................................................................... 109
Table 4.7: Least squares means of percent cover of grass, clover, weed, and dead material at
Blacksburg and Raphine, VA during 30 April 2013—28 Sept. 2014, averaged among
stocking methods and locations. ......................................................................................... 110
Table 4.8: Least squares means of percent cover of grass, legume, weed, and dead material at
Steeles Tavern, VA during 27 May –19 Oct. 2014, averaged among stocking methods. .. 110
Table 4.9: Least squares means of acid detergent fiber (ADF), crude protein (CP), neutral
detergent fiber (NDF), and total digestible nutrients (TDN) summarized by stocking
methods at Blacksburg and Raphine, VA during 2 May 2013—11 Oct. 2014, averaged
among time and locations. .................................................................................................. 111
Table 4.10: Pearson’s product-moment correlation coefficients for complete observations (n =
554) of acid detergent fiber (ADF), crude protein (CP), neutral detergent fiber (NDF),
herbage biomass, and cover of grass, white clover, red clover, dead material, and bare soil at
Blacksburg and Raphine, VA during 15 May 2013-11 Oct. 2014...................................... 112
Table 4.11: Pearson’s product-moment correlation coefficients for complete observations (n =
463) of acid detergent fiber (ADF), crude protein (CP), neutral detergent fiber (NDF),
herbage biomass, date of initiation of stocking, pasture rest period, 15-day soil temperature,
and 15-day accumulated precipitation at Steeles Tavern, VA during 19 May-18 Nov. 2014.
............................................................................................................................................. 113
Table 4.12: Least-squares means of concentrations of acid detergent fiber (ADF), crude protein
(CP), and neutral detergent fiber (NDF) in herbage sampled by beef steers and hand clipped
from continuous, mob, and rotationally stocked pastures at Blacksburg, VA during 28
Sept.—2 Oct. 2014. ............................................................................................................. 114
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LIST OF FIGURES

Figure 3.1: Locations of the study sites in Virginia. ..................................................................... 68
Figure 3.2: Paddock arrangements, dimensions, and sizes for the stocking methods study in
Blacksburg, VA..................................................................................................................... 68
Figure 3.3: Paddock arrangements, dimensions, and sizes for the stocking methods study in
Raphine, VA. ........................................................................................................................ 69
Figure 3.4: Arrangement of the stocked pastures in Steeles Tavern, VA. .................................... 70
Figure 3.5: Herbage sampling points in Blacksburg, VA.. ........................................................... 71
Figure 3.6: Herbage sampling points in Raphine, VA.. ................................................................ 72
Figure 4.1: Mean standing biomass at Blacksburg and Raphine, VA during 9 April 2013—15
Nov. 2014 by stocking method averaged among sampling periods and locations ............ 115
Figure 4.2: Mean standing biomass at Blacksburg and Raphine, VA during 9 April 2013—15
Nov. 2014 by sampling period averaged among locations and stocking methods ............ 116
Figure 4.3: Mean standing biomass in paddocks within (A) mob-stocked pastures and (B)
rotationally-stocked pastures, at Steeles Tavern, VA, respectively, averaged among samples
harvested during 19 May—18 Nov. 2014, as a function of date of initiation of stocking in
each paddock. ...................................................................................................................... 117
Figure 4.4: (A) Herbage accumulation and (B) herbage disappearance, respectively, during 2
May—15 Nov. 2014 at Blacksburg and Raphine, VA. ...................................................... 118
Figure 4.5: (A) Herbage accumulation and (B) herbage disappearance, respectively, during 22
July- 20 Nov. 2014 at Steeles Tavern, VA. ........................................................................ 119
Figure 4.6: Mean crude protein (CP) content of herbage at Blacksburg and Raphine, VA during 2
May 2013-11 Oct. 2014 by month of the study, averaged among locations and stocking
treatments. ........................................................................................................................... 120
Figure 4.7: (A) Response of crude protein (CP) content of herbage harvested at Blacksburg and
Raphine, VA during 15 May 2013—11 Oct. 2014, to the sum of red and white clover cover
in sampled quadrats and (B) response of neutral detergent fiber (NDF) content of sampled
herbage to dead cover in sampled quadrats. ....................................................................... 121
Figure 4.8: (A) Crude protein (CP) content of herbage at Steeles Tavern, VA during 19 May—22
Oct. 2014 by stocking treatment and (B) by month and stocking treatment interaction on
September 15 and October 22, 2014. .................................................................................. 122
Figure 4.9: (A) Acid detergent fiber (ADF) content of herbage at Steeles Tavern, VA during 19
May-22 Oct. 2014 by stocking treatment and (B) by month and stocking treatment
interaction on 15 Sept. and 22 Oct. 2014. ........................................................................... 123
Figure 4.10: Crude protein (CP) content of clipped herbage and bovine esophageal extrusa
harvested from mob stocked pasture strips at Blacksburg, VA during 28 Sept.—2 Oct. 2014,
averaged among pasture strips and steers. .......................................................................... 124
Figure 4.11: Crude protein (CP) content of herbage harvested from esophageal cannulas of beef
steers grazing in continuous, mob, and rotational stocking pastures at Blacksburg, VA
during 28 Sept.—2 Oct. 2014 ............................................................................................. 125
Figure 4.12: Diurnal variation in crude protein (CP) content of herbage harvested from
esophageal cannulas of beef steers grazing in mob stocked pastures at Blacksburg, VA
during 28 Sept.—2 Oct. 2014.. ........................................................................................... 126

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LIST OF EQUATIONS

Equation 3.1: Harvest index (HI) .................................................................................................. 53
Equation 3.2: Aboveground net primary productivity (ANPP) .................................................... 55
Equation 3.3: Annual herbage disappearance ............................................................................... 55
Equation 3.4: Total digestible nutrients (TDN) ............................................................................ 56
Equation 3.5: Initial repeated measure analysis of variance (ANOVA) model ............................ 58
Equation 3.6: One-way analysis of variance (ANOVA) model ................................................... 59

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ABBREVIATIONS

ANPP aboveground net primary productivity
ADF acid detergent fiber
ADG average daily gain
AIC Akaike Information Criterion
ANOVA analysis of variance
AUM animal unit month
BW body weight
Ca calcium
CP crude protein
CV coefficient of variation
DE digestible energy
DM dry matter
F Fisher-Snedecor variance ratio
FA forage allowance
GPS global positioning system
HI harvest index
HSD Tukey’s Honestly Significant Difference
IACUC Institutional Animal Care and Use Committee
IS index of selectivity
IVDMD in vitro dry matter digestibility
K potassium
LAI leaf area index
LS least squares
Mg magnesium
N nitrogen
NDF neutral detergent fiber
NIRS near infrared reflectance spectroscopy
NRC National Research Council
OM organic matter
P phosphorus
P probability
ρ Pearson’s correlation coefficient
PET potential evapotranspiration
R2 coefficient of determination
RFQ relative forage quality
RPM rising plate meter
SE standard error
SDC size density compensation
TDN total digestible nutrients
VT Virginia Tech
WSC water-soluble carbohydrates
𝑥̅ population mean

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