LCA Food 2012 in Saint Malo, France! - Manifestations et colloques ...

PARALLEL SESSION 3C: SHEEP AND DAIRY PRODUCTION SYSTEMS 8 th Int. Conference on LCA in the
Agri-Food Sector, 1-4 Oct 2012
The LCA analysis of the production of lamb meat thus has to take into account the different sizes of the
breeds and consequent feed requirements, different types of land and consequent yields of grass (and management
requirements), and different rates of lamb growth and ewe productivity.
The Cranfield LCA model addresses this using systems modelling to link the various sub-systems. The equations
linking the systems ensure that the numbers are coherent and enable various options to be analysed.
Options that can be explored may be economic, long term breeding goals, such as greater fecundity or policy
oriented, such as concentrating sheep production in the hills or lowlands, as land demand changes.
2. Methods
2.1 Functional unit
The functional unit (FU) is 1000 kg expected edible lamb carcass at the national level. This is derived as
liveweight for slaughter multiplied by the killing out percentage (47%), so that the system boundary is the
farm gate, but the FU represents the useful carcass weight that can be expected. The relatively small burdens
of transport and slaughtering are not included. Adult sheep meat and wool are co-products.
2.2 Biophysical performance of flocks
The basis of the model is the definition of the biophysical performance of each type of sheep flock. These
include terms for ewe and ram longevity, fecundity (lambs per ewe per year), ram/ewe ratios, growth rate,
mature body weights and mortality rates. This gives the data to calculate flock replacements required and
hence how many surplus lambs are produced for exports to other flocks or for slaughter (Table 1). Data came
from standard agricultural texts (e.g. Nix, 2005; Agro Business Consultants, 2005), contact with the industry
and further research (Warkup et al., 2008). It is important to note that a distribution of lamb weights comes
from each system, not just an average. Hill sheep are clearly smaller and shorter lived than lowland ones.
Table 1. Main characteristics of the sheep flocks
Hill pure
bred
flocks
Upland
purebred
flocks
Upland
crossbred
flocks
Lowland
purebred
flocks
Lowland
crossbred
flocks
Ewe life, years 3.5 4.3 4.3 4.3 4.3
Ram life, years 3 3 3 3 3
Ewes/ram 47 47 47 20 20
Annual ewe culling rate 5% 4% 4% 4% 4%
Annual ewe mortality rate 3% 3% 3% 3% 3%
Lambs per year 1.0 1.4 1.4 1.5 1.6
Ewe weight, kg 52 62 76 74 78
Lamb daily liveweight gain, kg/d 0.10 0.14 0.17 0.18 0.19
Lamb mean final liveweight, kg 28 34 38 38 39
Distribution of lamb weights
25-32, kg 92% 29% 2% 2% 1%
32-36, kg 8% 49% 23% 21% 17%
36-39, kg 0% 18% 38% 37% 35%
39-45.5, kg 0% 4% 36% 40% 46%
Wool, kg 2.1 2.9 2.9 3.1 3.1
2.2 Structural model of the national flock
The individual flocks are linked by a set of linear equations to allow transfers between them (e.g. a store
lamb moves from the hills to an upland or lowland flock to be finished). If the balance of production systems
is changed, the model recalculates the systems in order to supply the functional unit. The balance may be
altered by changing the productivity of one part, e.g. more lambs per ewe in upland flocks, or by changing
the proportions of hill, upland and lowland flocks. The linking equations have the following structure. The
solution is the amount, X, of each activity, i, that produces the desired mass of the functional unit, Z,
n
i
i i X z Z
1 Eq. 1
where zi is the output (types of sheep) of activity i, and also satisfies the set of flows between activities:
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