Milk production and methane emissions in dairy cows on production or exercise pastures with an automatic milking system.

Comparative studies between pasture-based dairy production and indoor confinement-based production have demonstrated that including pasture in the diet reduces enteric methane emissions. However, the effects of seasonal access to pasture, where animals are allowed outdoors only during parts of the year, have been less extensively studied. The aim of this study was to assess the effects of providing dairy cows with voluntary access to a production pasture compared with an exercise pasture on their performance and enteric methane emission. Thirty-two lactating Norwegian Red dairy cows, averaging 158 DIM, were divided into 2 groups and used in a changeover experimental design. The treatments included cows given 24-h access to either a production pasture (providing at least 50% of cows' daily DMI) with unlimited fresh grass and restricted indoor feeding, or ad libitum indoor feeding of silage with access to an exercise pasture with no expected herbage intake. Each changeover period included 2 wk of adaptation followed by 2 wk of recording, during which both treatments were fed the same grass silage and concentrates. Milk yield was recorded using an automatic milking unit, and indoor feed intake was recorded using access-controlled feed troughs and concentrate feeders. Enteric methane emissions were monitored using 2 GreenFeed emission monitoring systems: one positioned indoors, and one positioned outdoors adjacent to the production pasture. Cows on production pasture exhibited a lower milking frequency and reduced milk yield compared with cows on exercise pasture. However, cows on production pasture compensated for the lower milk yield by increased concentration of milk solids, suggesting that including a significant amount of pasture in the diet of dairy cows may not compromise energy-corrected milk production. Additionally, cows in the production pasture had significantly lower enteric methane emissions compared with cows in the exercise pasture. In conclusion, incorporating pasture into the diets of dairy cows, even if only for part of the year, has the potential to reduce the carbon footprint of dairy production.