Abstract/Summary

Agri-food by-products are underused feed resources with the potential to reduce dairy emissions, yet most studies examined rumen and manure stages separately, which mask whole-system effects and shift environmental burdens between stages. This study is the first to assess the effects of incorporating apple pomace (AP) and hempseed cake (HC) into dairy cow diets on nitrogen and methane (CH4) emissions, across the entire milk production chain, from rumen fermentation to downstream manure storage. A 3 (treatments) x 3 (Periods) Latin square design was used with 15 cows, treatment diets included (1) CON (control diet): basal diets with forage and concentrates; (2) AP: 10 % of AP replacing forage; (3) HC: 10 % of HC replacing concentrates. Faeces and urine outputs were collected separately from animals, for manure storage experiment. Feeding AP and HC decreased (P < 0.01), respectively, enteric CH4 production by 6.3 % and 6.7 %, CH4/feed intake by 10.6 % and 10.1 %, and CH4/milk yield by 9.8 % and 10.9 %. Inclusion of AP decreased urine N /total N intake, compared to CON and HC (P < 0.05). In manure storage, the AP decreased the cumulative ammonia (NH3) and CH4 emissions by 24.8 % and 27.4 % than CON, respectively (P < 0.05). The above mitigation actions through feeding AP and HC, when working together in implementation for feeding dairy cows, could decrease annual CO2 equivalent emissions by 13 % and 10 % respectively. This is the first integrated study combining rumen fermentation with manure impacts, showing that AP and HC inclusion can be a practical approach to mitigate emissions in dairy farming.