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PA3r:i:URE AVAILABILITY AND COMPOSITION IN RELATION TO
DIET SELECTION AND DIET QUALITY BY GRAZING SHEEP
A thesis
presented in partial fulfilment of the requirements for the degree
of
r~ASTER OF AGRICULTURAL SCIENCE
at
Massey University
Murray Clive Guy
1979.
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The Library
MASSEY UNIVERSITY
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ABSTRACT
Some factors influencing grazing behaviour, diet selection and diet quality by sheep were investigated.
The influences of pasture availability, accessibility, composition and digestibility on diet selection by grazing sheep at two stocking rates (24 and 36 sheep per hectare) over three-day grazing periods during two seasons (summer and autumn) were examined. The stocking rates were
replicated twice and measurements were recorded at six intervals, each a three-day grazing period., over the
summer and autumn seasons. Dietary samples were obtained
ii
by the use of oesophageal fistulated sheep, and comparisons between extrusa samples and cut pasture were made. Pasture type contrasted between seasons with extremes of availability, structure, accessibility and quality. These evolving
pasture types and their changing properties are discussed.
Sheep grazing pasture have the ability to be selective, the extent of diet selection being dependent on pasture
properties of availability, composition and quality.
Diet preference is for the green leaf component of the pasture with avoidance of matur~ stern and dead matter.
However in situations of low pasture availability and poor accessibility of the preferred green leaf component, increasing amounts of dead herbage were ingested, as was evidenced in comparisons between periods and during three- day grazing periods.
Digestibility values of the sheeps' diets are higher than corresponding values from available pasture the
magnitude of the difference being dependent on pasture composition, availability and accessibility, ie. the opportunity afforded for diet selection.
Descriptions of experimental site, climatic conditions and animal management are recorded. The results are discussed in relation to ~ther research findings, and their practical implications.
i i i
ACKNO'NLEDG "EMENTS
Professor B.R. 'Natkin' s gtlidance and encouragement was greatly valued.
Grateful acknowledgement is made also to Dr R. 'ii.
Brougham and Mr D.A. Grant for direction and assistance, rv:r R. G. Keogh and Mr P. Vlieg for skilled surgical
oesophageal fistulation; Dr V.J. Thomas for statistical advice and assistance; and other DSIR and ~assey
University staff for additional advice, services and assistance in analytical, photographic and productional aspects of this thesis.
Title and preface Abstract
Acknowledgements List of figures List of plates List of tables
CONTEiiTTS
INTRODUCTION
CHAPTER 1. LITERATURE REVIEW Outline
Introduction
Section 1. i Intake
i i Diet selection
i i i Digestibility
Section 2. i Methods· of diet evaluation
Page i ii iv
3
5 5 15
27 32 CHAPTER 2. EXPERI1\IENTAL OUTliNE, METHODS AND SCHEDULE
Outline
Methods and measurements Statistical methods
Schedule of experimental events CHAPTER
3.
RESULTS1. Pasture availability and 'utilization' 2. Pasture Composition
3.
Pasture Strata Composition52 59
66 67
69 73 79
L~. Animal extrusa Composition
85
5.
Pasture Composition : Animal Diet Composition90
6. Pasture Digestibility
7.
Pasture Strata Digestibility97
8. Animal Extrusa Digestibility
97 9.
Pasture Digestibility : Animal Digestibility97
10. Pasture Species 11. Weed Species
12. Oesophageal Fistula sheep liveweight 13 c Climate
102 107 107 108
CHAPTER L~.
i ii iii iv
v
APPENDICES
DISCUSSION
Experimental objective Experimental design Experimental methods Experimental Results.
A. Animal diet (1) Composition (2) Digestibility B. Stocking rate
General Conclusions and Practical Implications
BIBI,IOGR.~..PHY
113 114 115.
116 118 121 122 125
128 215
J.1IST OF FIGURES
1. Experimental Area and Layout 2. Pasture Availability - Summer
3.
Pasture Availability - Autumn 4.· Pasture Composition(%) -
Summer5.
Pasture Composition(%) -
Autumn 6.7·
8.
9 ..
10.
11.
12.
13.
14.
16.
17.
18.
'B' Strata Pasture Composition
(%) -
Summer 'T' Strata Pasture Composition(%) -
Summer Animal Extrusa Composition(%} -
Summer Animal Extrusa Composition(%) -
Autumn Pasture Digestibility (OMD%) -
Summer Pasture Digestibility (OM.D %) - Autumn Pasture Strata Digestibility (OMD%)
Animal Extrusa Digestibility (OMD
%) -
Summer Animal Extrusa Digestibility (OMD%) -
Autumn Pasture Digestibility : Animal ExtrusaDigestibility
Mean Monthly Rainfall Soil Temperature
Mean Monthly Windrun
56 70
71 7677
81 82
87
88
94 95 98 99
100
101 109 110 111
{
1.
2.
3.
4.
LIST OF PLATES
Experimental Overview - Late Summer (6-3-78) Experimental Overview - Autumn (19-5-78) Paddock Subdi visional Ele·ctric Fencing
Water Supply and Rock Salt Availability Hand Shears for Pasture Harvesting
6o Cannulae Plugs used in Oesophageal Fistulated Sheep.
53 53 58 58 61
7. Animal Bolus Extrusa 117
8. Autumn Pasture Availability 117
9.
Late-Summer Pasture Availability - Treatment L(6-3-78) 123
10. Late-Summer Pasture Availability - Treatment H
(6-3-78) 123
11. Post-Grazing Autumn Pasture Availability-
Treatment H (19-5-78) 124
12. Post-Grazing Autumn Pasture Availability -
Treatment L (19-5-78) 124
1.
2.
3.
4.
5.
6.
7.
8.
12.
14.
15.
16 ..
17 ..
18.
19 ..
20.
21.
22o
Percentage Utilization of Total Available Dry Matter
Percentage Strata Utilization of Total Available Dry Matter
Amount of Green Leaf (kg/ha)
Pasture Stem Availability (kg/ha) Amount of Dead Matter (kg/ha) Amount of Leaf (kg/ha)
Amount of Leaf per Strata (kg/ha)
Percentage Stem of Pasture Composition Strata Dead Matter Composition
(%)
Extrusa Dead J\1atter Composition (%)
Composition Comuarison : Pasture v Diet for Leai (L), Stem {S), Other Species (OS) and dead Matter (D)
(%)
Pasture (P) v Animal (A) Composition x Period Interaction
Pasture v Animal Composition x Days Interaction Pasture Digestibility (OMD
%)
(Periods x Days) Pasture Digestibility (OMD%)
(Treatments x Days)Pasture : Animal Diet Digestibility Comparison Species Contribution to Available Pasture
Availability of Lolium per~ (kg/ha)
Strata Availability of Lolium £8~~EJ1e (kg/ha) Strata Availability of .bJ5rostis tenuis (kg/ha) Availability of Holcus lans.tus (kg/ha)
Mean O.F. Sheep Liveweights (kg)
Page
73 73 74 78 79
83 8385 90
91 92 93 96 96
102 103
1 OLJ- '104
105 106 108
