Methane emissions and digestive physiology of non-lactating dairy cows fed pasture forage

The objective of this study was to identify intake and digestion characteristic(s) responsible for variation in methane (CH4) emissions from non-lactating cows fed pasture forage. Nine Friesian × Jersey cows ranked low, medium or high CH4 emitters [group means 15.3, 19.2 and 24.8 g kg-1 dry matter intake (DMI), respectively; P = 0.015] were selected from a herd of 302 lactating cows. The selected cows were dried-off, rumen-fistulated, and fed indoors on fresh pasture forage at 0700 and 1700. Voluntary feed intake (VFI), feeding behaviour and intake rates (IR) were measured over 5 d. Feed allowance was reduced to 90% of VFI for measurement of CH4 emissions and rumen fermentation and digestion kinetics parameters. Although some variation in CH4 yield remained among the animals (26.4 ± 3.6 g kg-1 DMI), the previous ranking of cows during lactation was no longer evident during this study (P = 0.41). The change in CH4 yields may have resulted from lower feed intakes of lower quality pasture compared with grazing. Regression analysis showed that absolute CH4 emission (g d-1) was best described by DMI and rumen acetate concentration (ACE) before the PM feeding (ACE 1700) (R2 = 0.88), whereas CH4 yield (g kg-1DMI) was mainly a function of ACE 1700 h alone (R2 = 0.84). We suggest that large animal-to-animal variations in CH4 yield are most likely associated with high intakes and concomitant effects of salivation and rumen digestion and passage.