Monensin controlled-release capsules for methane mitigation in pasture-fed dairy cows

This experiment was undertaken to evaluate controlled-release capsules (CRC) that released monensin, for the mitigation of methane production from cows. The evaluation has been bought about by government policies to lower agricultural greenhouse gas (GHG) emissions, whilst maintaining profitability of dairy farms in New Zealand. The experiment used 60 Friesian–Holstein cows fed ryegrass (Lolium perenne L.)-dominant pasture, starting in week 7 of lactation. The CRC were placed in the rumen of 30 cows and effects of monensin on milk production were measured over 11 weeks by comparison with 30 control cows (Con). Cows were grazed as a single herd for the majority of the trial, but 32 (16 CRC, 16 Con) were fed indoors for 36 days (four 9-day periods) for measurement of intakes and methane. Monensin CRC did not affect methane production, which averaged 19.7 g/kg dry matter intake (DMI). There were also no significant treatment effects on DMI (16.5 kg DM/day) and milk production (21.3 kg/day) when measured indoors or on milk production over the whole experiment (21.7 kg/day). Ruminal metabolites measured from five rumen-fistulated cows in either group were not significantly different. At the conclusion of the experiment, monensin release rate from the CRC (10.8 mg/kg DMI) retrieved from five fistulated cows averaged 52% of anticipated values. Inadequate performance of the controlled delivery device prevented an unequivocal evaluation of the monensin CRC for methane mitigation in dairy cows fed pasture.