Carbon footprint of cheese produced on milk from Holstein and Jersey cows fed hay differing in herb content

The objective of the study was to assess the impact on emission of greenhouse gases (GHG) of cheese production based on milk from different types of hay and breeds of cows in Denmark. An integral part of the study involved estimating GHG emissions from production of hay in a climate less favourable for field drying. The GHG emission was estimated using life cycle assessment (LCA) with kg of milk and kg of energy-corrected milk (ECM) delivered to the dairy and kg of cheese at the retailer as functional units (FU). Allocation at farm gate, between milk and meat, was made according to the biological relation between energy requirement for milk and meat production or as an economic allocation. Allocation at the dairy, between cheese and whey, was made either as an economic allocation or by system expansion. Inventory data were based on farm, herd and crop production data from commercial farms participating in research activities with controlled production of hay, in combination with either production information from cheese processing or literature estimates, all built into a static model. There was no effect on GHG emission per kg cheese of the proportion of herbs in the hay, but an effect of breed was found. The carbon footprint (CF) per kg cheese was lowest – 9.88 kg CO2 eq. – for milk from the Jersey herd compared with 12.1 and 12.7 from the two Holstein herds, although the GHG emission per kg milk at farm gate was highest from Jersey, but this was more than offset by a higher utilisation of Jersey milk for cheese production. The GHG emission from farm to retailer contributed less than 10% to total emissions, with the largest contribution from the energy used for cheese manufacture at the dairy, including storage. Methane was the largest source at approximately 50%, followed by feed production and the rearing of heifers. Use of energy for hay-drying added 7–8% to emissions and soil carbon change on average 3%, with some variation between farms. The sensitivity analysis showed that higher herb content could potentially reduce methane emissions by 6–7%, while the herbs' larger roots had only a marginal effect on GHG emissions from soil carbon at product level. If the feed conversion in Holstein breeds was assumed the same as in Jersey, the difference in emission per kg cheese due to breed was reduced but still lower from Jersey, which illustrates the positive effect of Jersey milk composition on cheese production efficiency.