The impact of selecting cows using the economic breeding index on methane output

A major challenge facing the agricultural industry is to reduce greenhouse gas emissions by 25% by 2030. The contribution of genetics should be considered when quantifying environmental impacts as breeding is cumulative and permanent; meaning any positive or negative effects of genetic selection will be compounded with successive generations. The economic breeding index (EBI) was developed to identify animals that increase profitability in grass-based dairy systems. Research has demonstrated the greater productivity and fertility of high EBI animals is associated with increased profitability. When enteric methane emissions are being counted nationally through inventory models all animals are treated equally. Within these models, it is assumed that increased productivity through genetic selection increases feed intake, which leads to greater enteric methane emissions. No data has been produced to say the contrary and therefore it is important to compare these estimations to measured data. 

Methane emissions were recently measured from a group of high EBI (Elite; EBI = €233) and a group of national average EBI (Nat Av; EBI = €133) dairy cows using enteric methane measurement devices. Enteric methane emissions were measured between March and October. The results are presented in Table 1. There was no significant difference in milk yield between the Elite and Nat Av. The Elite had greater milk fat and protein %, which resulted in an 8% greater milk solids yield compared to the Nat Av. Despite this, there was no significant difference in methane emissions between the Elite and Nat Av. The increased milk solids yield of the Elite resulted in a dilution of their methane emissions on a unit of output basis resulting in 7% less methane per unit of milk solids. As expected, the methodology applied in national inventory models calculated the Elite to emit significantly more methane per day compared to the Nat Av. This suggests that a proportion of the increased methane output associated with increased genetic merit within national inventories does not exist. Each €10 increase in EBI resulted in a 0.32% over estimate in enteric methane output. Further work is required to include genetic merit within inventory models. A new carbon sub-index will also be incorporated into the EBI later this year. This sub index will rank animals based on greenhouse gas emissions and will be linked to EBI through a price per tonne of carbon. This will put increased emphasis on traits which reduce carbon emissions such as fertility and maintenance, allowing for savings to be made in greenhouse emissions over the next decade.

Table 1. Effect of genetic group on milk production, and methane output

B. Lahart, F. Buckley, J. Herron, L. Shalloo (Teagasc Moorepark)