Assessing impact of grazing
management systems
Report number: 08FT197
Year of trial: 2009
Group that proposed: Fast lamb finishers
Region: South Otago
Introduction – background to the project
A key to successful lamb finishing or growing of ewe lambs, in a breeding and finishing or
purely finishing system, is the ability to grow lambs fast and maintain pasture quality. The
dairy farming industry has established very high per hectare production levels using
rotational grazing systems with „grazing rules‟ regarding residual cover, grazing duration,
and rotation length. These grazing rules are designed to maximise pasture growth and
pasture quality and hence animal performance per hectare. While these „grazing rules‟
are becoming widely understood and utilised by dairy farmers it is unclear to many sheep
farmers whether these systems are applicable to growing lambs. A long held view is that
lambs don’t “do” in large mobs with tight social pressure (as would be apparent in a
rotational system). There is therefore an opportunity to determine what rotational systems
rules maximise lamb growth rates in an intensive system.
Key aims – what was the project trying to achieve?
•
Compare growth rates of lambs (ewe lambs) in rotational versus a shuttle grazing
systems
•
Assess pasture quality changes in areas defined for shuttle and rotational grazing using
q-graze analy
Key findings & recommendations for farmers
•
In the short term (1 month) shuttle set stocked grazing of lambs achieves the greatest
performance in live weight gains
•
For periods of greater than 1 month, finishing lambs on a rotationally grazed system
could facilitate higher live weight gains through higher pasture quality.
•
Pasture quality is more easily maintained under rotational grazing
Methodology – what was done in the trial?
General
•
The trial started ~ 23st of January 2009. Climatic conditions prevented the start of the
trial in 2008.
•
The trial ran for 60 days ending the ~25th March +/- a couple of days between farms.
•
Recording sheets were provided for the data that needed to be collected at the
beginning and during the trial.
•
Pasture and grazing area management
•
Grazing areas were defined for each of the systems
•
Areas defined for each grazing group were equivalent (as much as possible) in grass
species and age.
•
The grazing area was defined on each trial farm by the size of the mobs in each
system (300 lambs, 500 lambs, and 700 lambs per grazing system). The area for each
system was equivalent.
•
Average pasture cover assessments were carried out at the beginning of the trial
period (combination of plate meter and eye assessment). An average pasture
assessment in each grazing block occurred at 30 and 60 days of the trial.
•
Average pasture quality assessments (using q-graze) were carried out at the
beginning of the trial period and at the end. Every paddock in each system was
assessed.
•
Pasture growth rate was assumed to be 30 kg DM/ ha/ day. With this in mind a simple
calculation was done to calculate stocking rate, intake, and cover change in the
rotational system
o
If opening cover is 1800 kg DM
o
Mob size is 500
o
3 ha paddock
o
Pasture growth rate is 30 kgDM/ ha
o
Time in paddock is 2 days
o
Lamb intake is 1.5 but need to offer 1.7 (Farmax modelled for ewe lambs growing
@ 180g/ day)
o
Closing cover calculated as follows:
500 lambs × 1.5 kgDM/ day × 2 days = 1500 kgDM in total
1500 ÷ 3 ha = 500 kgDM eaten/ ha
1800 – 500 = 1300 kgDM/ ha residual cover
Lamb management
•
The systems were run with ewe lambs, and the ewe lamb mob were divided
randomly in half
•
A sample of lambs (10% selected at random) was weighed from each trial group at
the beginning of the trial and the same group of lambs weighed at 20 day intervals (4
weights in total). Identification of these were by tag
•
FEC sampling was carried out every 20 days (at weighing times) for each trial group
and bulk tested (25 samples/ trial group). A sample was not required at the beginning
•
All lambs were drenched prior to entering each of the trial grazing systems
•
A threshold faecal egg count of 300 eggs/ gram (in either trial group) was used as the
level to trigger drenching of lambs in both trial systems. This was to remove a
treatment bias if one group was drenched and the other was not; particularly
important if selenium etc was in the drench
•
If lambs were shorn the date and length of time off pasture was recorded
•
If lambs were drenched or given cobalt (injection, drench, or on pasture) this was
recorded, and lambs in each system would receive the same.
•
A stocking rate was defined for each farm (depending on paddock and mob sizes)
and was equivalent between the two grazing systems, across the grazing area.
•
Lambs were offered 1.4 – 1.5 kgDM/ day
•
If ewes were used to control pasture in either system, the pre and post grazing covers
and time the ewes were present was recorded.
Rotational grazing rules
•
The following rules were adhered to when rotating lambs
o
Shift when cover was 1300kgDM/ ha (plate meter or eye measure)
o
Shift every 2 days (2-3 days depending on paddock size). If lambs were present
for longer than 3 days and 1300 kg DM cover was not reached, paddock size
needs to be reduced.
o
A round length of 18-22 days was used
Important notes
•
It was very important that animals in each of the grazing groups were treated the
same. i.e. if a treatment is given to one group, it should be given to the other group also
•
The idea of this was to compare the grazing systems within farms not between farms
•
No cattle were supposed to be introduced to either of the systems at any time
•
It is important that the grazing
Results
Three South Otago farms participated in the FITT “Fast Lamb Finishers‟ management trial,
including farms in Te Houka, Clydevale and Balclutha.
Data from the Te Houka property was excluded from the trial as pasture covers became
too low (owing to poor soil moisture) to support the trial.
Clydevale Farm
Lambs in both treatments started with the same (36.9kg) live weight. Lambs on the shuttle
set stocked treatment performed better than their rotationally grazed counterparts in
terms of live weight throughout the 63 day period as is shown in Figure 1. Shuttle set
stocked lambs also had higher live weight gains up until the last 19 days of the trial. In the
first 17 day period the set stocked lambs achieved on average 96 grams/day LWG more
than the rotationally grazed lambs. From days 18 to 42 of the trial the gap had narrowed
to 12grams LWG/day. Between the 6th and 25th March the set stocked lambs actually
recorded a 63g /day lower average live weight gain (Table 1). As a consequence, the
average live weight gains between the two treatments were similar with the set stocked
lambs recording only a 6 gram/day higher live weight gain over their counterparts over
the full trial period.
Figure 1. Average live weights of lambs grazed under a rotational and shuttle set stocked
system at Clydevale.
Figure 2. Live weight gains of lambs under a rotational and shuttle set stocked grazing
system at Clydevale.
Although there was not a great difference in lamb LWG‟s overall, Q graze estimated that
there was greater potential for the rotationally grazed paddocks to deliver higher live
weight gains for lambs if they were put onto the paddocks at the end of the trial. Given
the end pasture composition and quality of the rotationally grazed paddocks, Q graze
estimated that lambs could be able to achieve live weight gains of approximately
130g/day compared to 100g/day for lambs put in the set stocked paddocks. This was
attributed to greater pasture quality in the rotationally grazed pastures.
Table 1. Average pasture composition and quality at McAtamney’s farm for rotational
and set stocked paddocks.
% of total DM
as dead
matter
% of green
material as
clover
% of green
material as
green leaf
Q graze
estimate of
pasture quality
(MJME/kg DM)
Rotationally
grazed
12%
18%
82%
10
Shuttle set
stocked
18%
8%
92%
9.6
Balclutha Farm
On average the lambs on the Balclutha farm started at lower average live weights than
at Clydavale. For the rotational and set stocked lambs they started at 33.4 kg and 34.1 kg
respectively.
As is shown in Figure 3 and 4, in the first 26 days both treatments of lambs performed at
similar levels of live weight gains with the shuttle set stocked lambs achieving only 12g/day
higher live weight gains over the rotationally grazed lambs. In the 33 day period between
the 19th February and 24th March there was more of a contrast in live weight gain
performance. On average the shuttle set stocked lambs recorded a 12 g/day live weight
loss, while the rotationally grazed lambs managed to achieve 37 grams/day live weight
gain. This contributed to the lowering of the set stocked lambs overall live weight gains
making them 17g/day less on average over the trial period compared to rotationally
grazed lambs.
Figure 3. Live weights of finishing lambs under a rotational and shuttle set stocked grazing
system at Balclutha.
Figure 4: Live weight gains of lambs on rotational and shuttle set stocked grazing systems
at Balclutha.
Pasture quality figures between the two grazing treatments throughout and at the end of
the trial were very similar on the Telford Farm. Q graze estimated that the pasture quality
increased over the trial from 9.1 MJME/kg DM to 9.7 and 9.6 MJME/kg DM for the set
stocked and rotationally grazed paddocks respectively.
Table 2: Average pasture composition and quality at a Balclutha farm for the rotational
and shuttle set stocked lamb finishing paddocks.
Shuttle grazing
mid trial
Rotational grazing
mid trial
Shuttle grazing
end of trial
Rotational grazing
end of trial
% of total DM
as dead
matter
% of green
material as
clover
% of green
material as
green leaf
Q graze
estimate of
pasture quality
(MJME/kg DM)
6
23
87
9.1
27
21
89
9.1
19
19
83
9.7
20
21
93
9.6
Discussion
There were no high weight gains, by industry standards, in either set stock or rotational
grazing regimes at any of the trial sites. The timing of the trials may have been a factor,
with intermittent dry periods affecting pasture growth. The trial did serve to highlight the
relative merits of the two management systems.
Set stocking/ shuttle grazing
During the initial period of the trial, lambs under set stocking achieved a similar or higher
rate of live weight gain than those under rotation.
Higher initial live weight gains in the set stocked lambs at Clydevale could be due to there
being a higher initial pasture cover available to those lambs. Although average pasture
covers were similar initially, the rotational paddocks did not have had a proper feed
wedge, this could have meant there was a lower pasture allowance during the first
rotation. There is also the ability for set stocked animals to be more selective in the
material they eat, allowing a greater intake, but ultimately reducing the feed quality
available as the trial progressed. The final feed quality difference between set stocked
and rotational treatments support this observation
During the latter part of the trial the rotationally grazed lambs tended to perform better
relative to the set stocked lambs. At the Balclutha farm there was no difference in pasture
quality between the treatments initially, however there was an increase in pasture quality
from the mid to the end of the trial for both treatments. Therefore, non-pasture quality
factors such as variation in lamb gut fill at weighing and variations in pasture allowance
between the two treatments could be responsible for the differences in lamb
performance between the rotationally grazed and set stocked lambs.
It appears that lamb performance tends to reduce in a set stocked system if they are kept
there for too long and that it may be easier to improve pasture quality under rotationally
grazed pastures. This allows rotationally grazed lambs to make up on initially lower live
weight gains relative to set stocked lambs.
However, this trial did not allow for other classes of stock to be included in the trial. In a
normal farm situation a farmer generally has the ability to put other classes of stock such
as cattle into the set stocked paddocks in order to maintain quality.
A conclusion from these results is that while rotationally grazing lambs may not have
achieved the greatest finishing performance in the short term, it seemed that rotationally
grazed pastures may have facilitated greater pasture quality by the end of the period.
This suggests that if lambs continued to be finished on the rotationally grazed paddocks
the differential in lamb performance may increase in favour of the rotationally grazed lambs.