It is possible to incorporate environmental value into breeding goals
Take Home Message: Breeding dairy cows for increased yield will reduce the CO2 output from dairy farming by 0.6% for every 1% increase in yield.
A non-market or ‘shadow’ environmental value can be incorporated into selection indices, using increased milk yield to reduce the herd size required to maintain herd output as the goal trait.
“And a similar framework could be applied to other traits under selection to estimate a new suite of relative economic values that consider combinations of market and non market traits – both positive and negative,” SAC’ Eileen Wall told delegates at this year’s British Society of Animal Science annual conference.
Her team set out to outline methods for incorporating the environmental value of emissions mitigation into breeding goals. And the work revealed that many of the other traits included in £PLI, such a lifespan and health and fertility traits, will also have an additional favourable impact on greenhouse gases (GHG) emissions by improving overall system efficiency.
The economic appraisal of GHG emissions is complex. The ‘shadow’ price of carbon (SPC) is derived from the best estimate of the present value of damages associated with a tonne of GHG emission in carbon dioxide equivalents (CO2 eq).
“The SPC rises with time, reflecting the increasing marginal damage of a tonne of GHG when added to a growing stock of atmospheric GHGs.
“And there are many possible technical mitigation options for livestock systems, one of which includes harnessing selection tools,” she explained.
A previous study described how relative economic values (REVs) are calculated for traits included in the UK dairy profit index (£PLI) using dynamic programming tools to model a whole farm system. The REV for each trait is calculated by examining the consequence of a unit change in a trait of interest on net farm revenue, while keeping all other traits in the index fixed.
The SPC provides a useful mechanism of considering the costs of GHG emissions in an economic index framework, such as £PLI.
Methane, CH4 (enteric fermentation and manure storage), and nitrous oxide N2O (manure storage) emissions from the whole farm system (young stock and milking herd) were used to calculate REVs for £PLI. The N2O emissions due to nitrogen excretion when cows are grazing were also included.
And the shadow cost to the dairy herd of GHG emissions was calculated by multiplying the current value of the SPC – £26.50/t CO2 eq in 2008 – by the total GHG emissions from the system.
“The REV considering the SPC for milk yield was then calculated by increasing milk yield in percentage units while holding all other traits fixed,” said Dr Wall. “The impact of improving milk yield on GHG emissions and, therefore, the overall shadow cost of emissions to the farm is that fewer cows and followers are required to maintain a fixed herd output.”
And the work found that the largest proportion of GHG emissions from the defined dairy system is due to enteric fermentation in the milking herd, with more than 59% of the total GHG emissions.
“The young stock contributed more than 20% of the total GHG emissions, which included CH4 from enteric fermentation and CH4 and N2O from manure storage. And, overall, the dairy system produced approximately 791 tonnes of CO2 equivalent per year.
“This equated to annual shadow cost to the dairy herd of £20,957 per year, or 1.95ppl of milk produced.”
Improving milk yield by 1% decreased the GHG emissions from the dairy system by 4.8 tonnes CO2 equivalent. And this resulted in a new annual shadow cost to the dairy herd of approximately £20,830 per annum (or 1.94ppl of milk) – a reduction of £127 per annum.
“The SPC REV for milk yield was calculated to be £0.012ppl of milk per cow per year, or £3.64 per genetic standard deviation unit,” added Dr Wall.
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Adding this to the current £PLI would result in a relative weight in the index of 6% compared to the other production and functional traits already incorporated in £PLI.”
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