The sensitivity of comparative milk footprints from dairy farm systems implementing conventional and legume-based animal diets to choice of allocation method was assessed in this MScCAFFS thesis, this was achieved by gaining an understanding of LCA, CF, allocation methods, and system expansion, the Scottish dairy industry, legume-based animal diets, and genetics.

As discussed LCA and CF are methods that allow for the environmental impact of products and supply chains to investigated (Broekema et al., 2014; Dalgaard et al., 2008). Allocation methods are an important part in LCA. The allocation methods used were mass and economic allocation, the different methods of allocation can vary in results, so choosing the most suitable method is critical (Rice et al,. 2017). This was shown in the results as mass allocation had a higher EF then the economic allocation in all of the diet groups. Table 7.1 shows the averages for both the control and select cows on the by product diet, the mass allocation by product control group (BPC) on average had an EF of 4.83kg CO₂-eq/L while the economic BPC had an EF of 1.18kg CO₂-eq/L. This is a difference of 3.65kg CO₂-eq/L. Table 7.1 also shows the product select group (BPS) on average had an EF of 4.28kg CO₂-eq/L while the economic BPS had an EF of 1.04kg CO₂-eq/L. This is a difference of 3.24kg CO₂-eq/L. The difference in the other feed groups is not a high but there is still a difference.

Table 7.2 shows the averages for both the control and select cows on the high forge diet, the mass allocation high forage control group (HFC) on average had an EF of 1.87kg CO₂-eq/L while the economic HFC had an EF of 1.31kg CO₂-eq / L. This is a difference of 0.56kg CO₂-eq/L. The high forage select group (HFS) on average had an EF of 1.52kg CO₂-eq/L while the economic HFS had an EF of 1.17kg CO₂-eq / L. This is a difference of 0.35kg CO₂-eq/L.

Table 7.3 shows the averages for both the control and select cows on the low forge diet, the mass allocation low forage control group (LFC) on average had an EF of 1.53kg CO₂-eq/L while the economic LFC had an EF of 1.04kg CO₂-eq / L. This is a difference of 0.49kg CO₂-eq/L. The low forage select group (LFS) on average had an EF of 1.30kg CO₂-eq/L while the economic LFS had an EF of 0.91kg CO₂-eq / L. This is a difference of 0.39kg CO₂-eq/L.

Table 7.4 shows the averages for both the control and select cows on the home grown diet, the mass allocation home grown control group (HGC) on average had an EF of 2.36kg CO₂-eq/L while the economic HGC had an EF of 1.21kg CO₂-eq / L. This is a difference of 1.15kg CO₂-eq/L. The home grown select group (HGS) on average had an EF of 2.18kg CO₂-eq/L while the economic HGS had an EF of 1.13kg CO₂-eq / L. This is a difference of 1.05kg CO₂-eq/L. This shows that the type of allocation used can have a major effect on the EF per unit of output.

Reducing emissions is going to be critical for farming in the future. Climate change is becoming an ever-growing concern and it is causing a push to decarbonise areas such as transport, industry and agriculture. The agricultural sector must also find ways to reduce their footprint (Hoegh-Guldberg et al., 2018; Rogelj et al., 2018).

Improving the genetic merit of dairy cows is a way that the dairy industries footprint can be reduced (Ross et al., 2014; Vellinga et al., 2018). This was shown in the results in all the groups the select cow groups had a low EF per litre of milk then the control cows groups. Table 7.1 shows the control and select cows on the by product diet. The select cows on average had a milk yield of 545373.5 litres and an economic allocation EF of 1.18kg CO₂-eq/L while the control cows had an average milk yield of 433420.5 litres and an economic allocation EF of 1.04 kg CO₂-eq/L. This is a difference of 0.14kg CO₂-eq/L. The select cows had a mass allocation EF of 4.28kg CO₂-eq/L while the control cows had a mass allocation EF of 4.83 kg CO₂-eq/L. This is a difference of 0.55kg CO₂-eq/L.

Table 7.2 shows the control and select cows on the high forge diet. The select cows on average had a milk yield of 433,361 litres and an economic allocation EF of 1.17kg CO₂-eq/L while the control cows had an average milk yield of 405,650 litres and an economic allocation EF of 1.30kg CO₂-eq/L. This is a difference of 0.13kg CO₂-eq/L. The select cows had a mass allocation EF of 1.52kg CO₂-eq/L while the control cows had a mass allocation EF of 1.87kg CO₂-eq/L. This is a difference of 0.35kg CO₂-eq/L.

Table 7.3 shows the control and select cows on the low forge diet. The select cows on average had a milk yield of 533,950.2 litres and an economic allocation EF of 0.91kg CO₂-eq/L while the control cows had an average milk yield of 479,329 litres and an economic allocation EF of 1.04kg CO₂-eq/L. This is a difference of 0.09kg CO₂-eq/L. The select cows had a mass allocation EF of 1.30g CO₂-eq/L while the control cows had a mass allocation EF of 1.53kg CO₂-eq/L. This is a difference of 0.23kg CO₂-eq/L.

Table 7.4 shows the control and select cows on the low forge diet. The select cows on average had a milk yield of 424,024 litres and an economic allocation EF of 1.13kg CO₂-eq/L while the control cows had an average milk yield of 356,441litres and an economic allocation EF of 1.21kg CO₂-eq/L. This is a difference of 0.08kg CO₂-eq/L. The select cows had a mass allocation EF of 2.18g CO₂-eq/L while the control cows had a mass allocation EF of 2.36kg CO₂-eq/L. This is a difference of 0.18kg CO₂-eq/L. This shows that improving genetics increases yield and in turn reduces the EF per unit of output.

The inclusion of legumes in diets could help achieve the goal to reduce footprints. The results showed how different diets can cause major differences in the associated emissions. The different diets had an effect on the EF on each of the diets. Table 7.2 shows both the economic and mass allocation of the control and select cows on the high forge diet, Table 7.3 shows both the economic and mass allocation of the control and select cows on the low forge diet. The economic allocated HFC had an average EF of 1.31kg CO₂-eq/L, while the economic allocated LFC had an average EF of 1.04kg CO₂-eq/L. This is a difference of 0.27kg CO₂-eq/L. The mass allocated HFC had an average EF of 1.87kg CO₂-eq/L, while the mass allocated LFC had an average EF of 1.53kg CO₂-eq/L. This is a difference of 0.34kg CO₂-eq/L. The low forge diet had lower EF then the high forge diet for both of the allocation methods.

Table 7.1 shows both the economic and mass allocation of the control and select cows on the by product diet, Table 7.4 shows both the economic and mass allocation of the control and select cows on. The economic allocated BPC had an average EF of 1.18kg CO₂-eq/L, while the economic allocated HGC had an average EF of 1.21kg CO₂-eq/L. This is a difference of 0.03kg CO₂-eq/L. The mass allocated BPC had an average EF of 4.83kg CO₂-eq/L, while the mass allocated HGC had an average EF of 2.36kg CO₂-eq/L. This is a difference of 2.2kg CO₂-eq/L. The home grown diet had a lower EF then the by product diet when mass allocation was used, but the by product diet has a lower EF then the home grown diet when economic allocation was used. This shows that different feeds within the diet can cause changes in the EF. It was expected that the BPC would have had a lower EF then the other diets as it included more legumes then the other diets, and as it name suggests it uses by products which can reduce the amount of human edible protein being included in dairy feed.

The bar chart in Figure 7.1 and the boxplot in Figure 7.2 show all the cow groups together and their average EF per litre of milk (kg CO₂-eq/L). It visually shows that across all of the groups mass allocation generated a higher footprint then economic allocation. And it can be seen that the select cows had higher milk yield then the control cows and in turn a lower Milk EF (kg CO₂-eq/L).

Overall the results show it is possible to see the difference allocation methods, different diets and genetic merits can have on the footprint generated in dairy systems. It also means that milk footprints can be changed at farm level though breeding programmes, careful management of diets and selecting the most suited allocation method. Breeding programmes will increase the herds genetic merit and yields, careful managing diets will allow for a balance between adequate nutrition for the animals and low footprint diets. Both are important strategies to achieve the planned carbon-neutral goals being set.  

Conclusion

The purpose of this MScCCAFS thesis was to assess the sensitivity of comparative milk footprints from dairy farm systems implementing conventional and legume-based animal diets to choice of allocation method. This purpose was achieved by assessing the sensitivity of comparative milk footprints from dairy farm systems implementing conventional and legume-based animal diets to choice of allocation method. An understanding of and LCA, CF, allocation methods and system expansion, the Scottish dairy industry and legume-based animal diets was generated.

The results were as expected, EF and footprints are affected by different allocation methods, diets and genetics. The EF figures generated were successfully examined and compared.

Overall it was found that milk footprints are sensitive to different allocation methods, diets and genetics. So understanding these could allow for milk footprints to reduced as these areas can be controlled at farm level. Mass allocation had a higher footprint then the economic allocation for all of the diet groups, the cows with high genetic merit had a lower footprint, the footprints for each of the diets varied considerably across all the diets.

It was found that managing diets and genetics, and selecting an allocation method can create large variance on milk footprints.

If this project was carried out again evaluating more herds, over longer periods of time and in different locations would allow for a more accurate and more representative result to be obtained.