Primer ciclo: Reconocimiento de los ambientes de aprendizaje de la clase de

Broiler production systems in the UK are fairly consistent, and the two systems studied

represent 95% of UK broiler production (RSPCA, 2008). Williams et al. (2006) used LCA

based on a systems modelling approach to study broiler production, and expressed the

results on a dead weight basis. This model was developed further under DEFRA-funded

project IS0222 and modified to express GHG emissions on a live weight basis for

comparison with the current study. The results were 12,213 MJ and 2,016 kgCO2e/tonne

live weight for fossil energy use and GHG emissions respectively (Williams, pers. comm.

2011). In the current study, fossil energy use for the ‘Standard’ production system, using

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reported by Williams et al. (2006). However, their results are based on litter disposal to

land as an organic fertiliser. When compared with the litter to fertiliser scenario in the

current study, differences in energy and GHG emissions were only 9% and 2%

respectively. Results obtained in the current study were based on data collected from

farms to account for economic flow, and databases and calculations to provide ‘static’ life

cycle inventories. In contrast, systems’ modelling provides more ‘dynamic’ life cycle

inventories which respond holistically to change. Although the approach adopted by

Williams et al. (2006) was different to that adopted in the current study, the results are in

good agreement.

Katajajuuri et al. (2008), cited in de Vries and de Boer (2010), provide results of 16,000

MJ and 2,079 kg CO2e/tonne live weight for energy use and GHG emissions arising from

broiler production in Finland, based on data collected from farms. These results are

significantly higher than those obtained in the current study. In contrast, the life cycle

inventory for broiler production for Denmark derived from the LCA food database (Nielsen

et al., 2003), included in the Simapro databases, provides results of 9,420 MJ and 1,820

kg CO2e/tonne live weight, which are similar to those obtained in the current study.

However, in the Danish products system modelled, significant credits are gained from the

avoidance of rapeseed oil production through the co-production of soya oil when soya

bean meal is produced. In the current study, system expansion is only used for disposal of

wash water, litter and mortalities. Thus, these studies are not directly comparable.

Pelletier (2008) using data collected from farms, reported energy use and GHG emissions

of 14,900 MJ and 1,395 kg CO2e/tonne live weight respectively for the US broiler industry.

For energy use and GHG emissions these results are higher and lower respectively than

those obtained in the current study. Pelletier (2008) partitions 80% of energy use to feed

production, with 18% being used on farm and 2% being attributed to chick production. In

the current study, 62% of fossil energy was used for feed production and delivery, with

35% being used on farm and 3% for chick production. The percentage of energy used for

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current study. In addition, litter disposal accounted for -1,613 MJ/tonne live weight, which

represents a lower credit than that of the litter-to-power scenario presented in the current

study.

In the study of Pelletier (2008), feed production was associated with energy use and GHG

emissions of 6,920 MJ and 612 kg CO2e/tonne respectively. These values are 65% higher

for energy use and 51% lower for GHG emissions than those obtained in the current

study. Pelletier (2008), allocates GHGemissions to co-products based on gross energy.

However, in the current study, ingredient life cycle inventories were derived from

databases, such as the Ecoinvent database, which normally use economic allocation

factors. As the approach to allocation adopted by the two studies was different, the results

are not directly comparable. The use of economic allocation is probably more appropriate

for feed production as the reason for processing is to provide a product to fulfil a human

need in exchange for economic revenue. In the current study, the environmental burden

associated with processing is ascribed to the co-products in proportion to their revenue as

recommended (Guinee et al., 2004; BSI, 2008b).

One of the major differences between the study reported by Pelletier (2008) and the

current study relates to FCR. Pelletier (2008) reported a FCR of 1.9, which is 10% greater

than that reported in the current study. If the FCR of birds in the ‘Standard’ production

system using litter-to-power scenario had been similar then fossil energy use and GHG

emissions would have been 9,724 MJ and 1,967 kgCO2e respectively. Differences in FCR

may be related to the economics of broiler production. A worse FCR may be accepted

from a cheaper diet if overall profitability is increased. The aggregate diet reported by

Pelletier (2008) consisted of 70% US corn, 20% US soya bean meal, 2.5% poultry by-

product meal, 2.5% poultry fat, 2.5% US menhaden meal and 2.5% salt and limestone,

which is significantly different to those presented in Table 21, with the main ingredient

being corn instead of wheat. In addition, UK broiler diets contain a higher proportion of

vegetable protein sources as the inclusion of terrestrial animal by-products in farm animal

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for US corn reported by Pelletier (2008) were 328 kg CO2e/tonne, which is mid-way

between the values for the same product derived from the Ecoinvent databases

(Ecoinvent Centre, 2010) and US Life Cycle Inventory (NREL, 2008) respectively. All of

these values are considerable lower than the value of GHG emissions for wheat, derived

from the Ecoinvent database and used in the current study. In addition, US soya bean

meal production does not incur emissions associated with land transformation. The use of

corn instead of wheat as the main dietary ingredient and US soya bean instead of

Brazilian soya bean are probably the main reasons for lower GHG emissions reported for

the US broiler industry.