Download New Methods for Identification and Evaluation of Intake

Iger-2003
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I G E R I N N O VA T I O N S
2003
New Methods for
Identification and
Evaluation of Intake
Characteristics
o f G r a s s Va r i e t i e s
Robert Orr and James Cook
Grass breeding and testing
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Measuring grass intake potential
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Correlation of intake with plant characteristics 31
Measuring bite mass
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2003
I G E R I N N O VA T I O N S
NEW METHODS FOR IDENTIFICATION AND EVALUATION
OF INTAKE CHARACTERISTICS OF GRASS VARIETIES
NEW METHODS FOR IDENTIFICATION AND EVALUATION
OF INTAKE CHARACTERISTICS OF GRASS VARIETIES
Robert Orr and James Cook
P
lant breeding priorities at IGER have
gradually changed since the establishment of
grass breeding at the former Welsh Plant Breeding
Station in 1919, reflecting the changing needs of the
farming community and society at large. The current
Livestock production systems based on grazing
offer
a
greater
probability
of
long-term
environmental sustainability than those based on
high levels of concentrate supplementation or using
housed animals.
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interest in and emphasis on grazing is based, in part,
Grass breeding and testing
on a need to reduce the costs of livestock production
Ideally, grass varieties should be bred to satisfy the
in order to sustain a viable UK agriculture which can
particular requirements of specific grazing systems
operate in world markets. There is a need to produce
and be evaluated using appropriate methodologies.
meat and milk using welfare-friendly methods in
This may not necessarily mean breeding for
pastoral systems that consumers perceive to be
increased intake and production, if it is at the
'natural'. There is also a need to minimise pollution.
expense of other desirable traits.
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Measuring grass intake potential
grasses consider 'simulated grazing' yield (measured
In order to investigate the extent of any differences
using frequent cutting), midseason digestibility,
in grass intake potential under grazing, 15
ground cover, winter hardiness and disease
intermediate-heading perennial ryegrass varieties,
resistance. We propose that for varieties destined for
with five replicate paddocks of each variety, were
grazing use, identifying grazing-related traits would
compared under continuous variable stocking
facilitate the development of varieties for grazing
management with sheep (Figure 5.1). Daily herbage
with reliable selection criteria. Screening varieties
intake was measured using alkane markers in grass
for intake characteristics would also identify those
and faeces, along with eating time which was
which are best suited to particular grazing systems.
measured using the IGER Behaviour Recorder
(http://www.ultrasoundadvice.co.uk), and mean
Large-scale grazing trials for routine variety
intake rate was calculated. There were marked
assessment are expensive in terms of land, animal
differences (Figure 5.2) in intake rate amongst the
and labour resources, and require quantities of seed
diploid (d), tetraploid (t) and tetraploid hybrid (th)
that may not be available in the early stages of
varieties tested with some having values nearly 20
variety development. In addition, the potential value
% higher or more than 20 % lower than the control
of grass cultivars under grazing cannot necessarily
variety for this heading group (Fennema).
be drawn from feeding value assessments with
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describes some of the methods under development.
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sheep and cattle grazing at a field scale. This article
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traits that are correlated with herbage intake by
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subsequent evaluation for the identification of plant
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scale, low-cost screening methods that are required
20
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At IGER, therefore, we are developing rapid, small-
Intake rate % of Fennema
housed animals.
NEW METHODS FOR IDENTIFICATION AND EVALUATION
OF INTAKE CHARACTERISTICS OF GRASS VARIETIES
Current UK national testing procedures for forage
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Iger-2003
Fig 5.2 Intake rate as a percentage of that for the control variety
Fennema in diploid (d), tetraploid (t) and tetraploid hybrid (th)
intermediate-heading perennial ryegrass varieties when grazed by
sheep under continuous stocking management.
Correlation of
characteristics
intake
with
plant
To relate these differences in intake to plant
characteristics which could be targeted in grass
breeding programmes, intake measurements were
Figure 5.1 Aerial view of the grass variety evaluation grazing trial
with sheep
made on five grass varieties (AberDove, Belramo,
Glen, AberExcel and Twins) along with a suite of
detailed chemical (digestibility, nitrogen and water
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MORPHOLOGICAL MEASUREMENTS
NEW METHODS FOR IDENTIFICATION AND EVALUATION
OF INTAKE CHARACTERISTICS OF GRASS VARIETIES
Morphological measurements included: extended tiller and sheath tube lengths; partition of herbage mass
into leaf, pseudostem and dead fractions; number of tillers per unit ground area; leaf area index (leaf area
per unit ground area); leaf weight per unit leaf area and the vertical distribution of leaves within the swards
using an inclined point quadrat (Figure 5.3a, 5.3b).
Fig 5.3a An inclined point quadrat with the pin mounted at 32.5o
to the horizontal. The height of each contact with plant parts is
recorded as the pin travels from the sward surface to the ground.
This allows the calculation of a number of sward parameters.
(mm)
60 - 65
AberDove
Belramo
Glen
AberExcel
Fig 5.4. Measuring leaf area using a planimeter.
Twins
55 - 60
50 - 55
45 - 50
40 - 45
35 - 40
30 - 35
25 - 30
20 - 25
15 - 20
10 - 15
5 - 10
0-5
0.00
0.50
1.00
0.00
0.50
1.00
0.00
0.50
1.00
0.00
0.50
1.00
0.00
0.50
1.00
No. of leaf contacts per descent
Fig 5.3b. Number of leaf contacts – this is a measure of leaf density
and plant architecture obtained using an inclined point quadrat
instrument.
Fig 5.5.Measuring plant dimensions.
soluble
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carbohydrate
concentrations)
and
Measuring bite mass
morphological factors (see box above).
Currently, short-term, small scale assessment
There were significant differences between the five
methodologies are being developed to measure bite
contrasting varieties in ingestive and ruminative
mass. Evaluations used boxes (dimensions 85 x 44 x
behaviour, in plant morphology and in plant
14 cm) containing compost growing medium sown
chemistry. An example of potentially important
with either Belramo, Glen, AberExcel or Rosalin
morphological data is shown in Figure 5.5b. Work is
varieties at a sowing rate of 1600 seeds m-2 (Figure
now in progress to identify plant traits that are
5.6). The boxes were kept in a glasshouse and the
correlated with grass intake.
grass cut to 6 cm from the soil surface at 5 and 8
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Fig 5.8 Measuring bite mass
weeks after sowing. They were moved outdoors to
an arena before each test, in which each variety was
The tests were recorded on video and the actual
offered to one of four yearling Simmental x Holstein
number of bites was determined (Figure 5.8). The
heifers 11 weeks after sowing in an experiment with
heifers ate the grass readily from the boxes and the
a Latin-square design.
mean time between the 'before' and 'after' weighings
Each box was weighed accurately (± 0.1 g) before
was 8 min. A mean number of 51 g 3.9 bites was
and after a period in which the heifer was allowed to
taken. Bite mass tended to be higher for Glen than
take approximately 50 bites (Figure 5.7). Samples of
Belramo (diploids) and higher for AberExcel than
the grasses were weighed, dried and then weighed
Rosalin (tetraploids), similar to rankings for intake
again in order to calculate bite mass (dry matter).
rate when these varieties were grazed in the field by
NEW METHODS FOR IDENTIFICATION AND EVALUATION
OF INTAKE CHARACTERISTICS OF GRASS VARIETIES
Fig 5.6 Sward boxes sown with ryegrass
continuously-stocked sheep (Figure 5.2). The
technique provided a relatively quick assessment of
intake characteristics of the four grass varieties.
In 2003, ingestive behaviour will be measured for
groups of heifers rotationally stocked in 1-day
paddocks on these same varieties and compared with
data from the short-term methods. If successful, the
methodologies developed in this project could be
used by plant breeders and variety evaluators to
identify useful genetic material and produce grass
varieties optimised for grazing systems for a range of
circumstances/managements.
This work has been funded by DEFRA.
Contact; [email protected] or
[email protected]
Fig 5.7 Weighing sward box
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