Greenhouse gas emissions and nitrogen efficiency of dairy cows of divergent economic breeding index under seasonal pasture-based management

摘要

Greenhouse gas (GHG) emissions and nitrogen (N)efficiencies were modeled for 2 genetic groups (GG)of Holstein-Friesian cows across 3 contrasting feedingtreatments (FT). The 2 GG were (1) high economicbreeding index (EBI) animals representative of the top5% of cows nationally (elite) and (2) EBI representativeof the national average (NA). The FT represented (1)generous feeding of pasture, (2) a slight restriction inpasture allowance, and (3) a high-concentrate feedingsystem with adequate pasture allowance. Greenhousegas and N balance models were parameterized usingoutputs generated from the Moorepark Dairy Systemsmodel, a stochastic budgetary simulation model, havingintegrated biological data pertaining to the 6 scenarios(2 GG × 3 FT) obtained from a 4-yr experiment conductedbetween 2013 and 2016. On a per hectare basis,total system GHG emissions were similar for both eliteand NA across the 3 FT. Per unit of product, however,the elite group had 10% and 11% lower GHG emissionsper kilogram of fat- and protein-corrected milk and perkilogram of milk solids (MSO; fat + protein kg), respectively,compared with the NA across the 3 FT. TheFT incorporating high concentrate supplementationhad greater absolute GHG emissions per hectare as wellas GHG per kilogram of fat- and protein-corrected milkand MSO. The elite group had a slightly superior N useefficiency (N output/N input) and lower N surplus (Ninput – N output) compared with the NA group. Thehigh concentrate FT had an inferior N use efficiencyand a higher N surplus. The results of the current studydemonstrate that breeding for increased EBI will leadto a general improvement in GHG emissions per unitof product as well as improved N efficiency. The resultsalso illustrate that reducing concentrate supplementationwill reduce GHG emissions, GHG emissions intensity,while improving N efficiency in the context ofpasture-based dairy production.