Feeding concentrate pellets to early-lactation cows consuming spring ryegrass pasture did not reduce methane emissions

Context Feed additives containing methane-reducing compounds are effective where dairy cows are fed a total mixed ration. In pasture-based systems, there are challenges incorporating feed additives into the diet, although one potential delivery mechanism is through inclusion into concentrate supplementary feed. However, the use of supplementary feed encounters seasonal complexities, particularly in spring when high-quality pasture supply often equals feed demand. If feed additives were to become a methane mitigation option for pasture-based systems, it is important to determine the impact of concentrates on dairy cow methane emissions (g/day, g/kg DM, and g/kg milk solids), and system profitability. Aim This study aimed to evaluate the performance (dry-matter intake (DMI), milk production, and methane emissions) of early lactation dairy cows offered spring perennial ryegrass-based pasture (PAS) or PAS plus 4 kg DM/cow.day of a supplementary concentrate feed (SUP) fed as 2 kg DM/cow during AM and PM milkings. Methods Forty lactating (89 ± 2 days in milk (DIM), mean ± s.e.m.) Holstein-Friesian dairy cows were randomly assigned to one of two treatments (PAS or SUP). Following a 3-week dietary adaptation period outdoors, cows were housed indoors for 25 days in a Calan Gate System and continued in their treatment groups (PAS or SUP) with fresh pasture fed twice daily. Milk production was recorded daily, milk composition determined weekly, and gas emissions measured daily by using GreenFeed technology. Results Cows in the SUP treatment had 7.6% greater total DMI (19.2 vs 17.9 ± 0.3 kg DM/day, P < 0.01) and 6.9% greater milk solids (MS) production (2.02 vs 1.89 ± 0.04 kg MS/day, P = 0.02) than did PAS cows. Cows in the SUP treatment tended to produce more methane (395 vs 376 ± 7 g CH4 g/day, P = 0.08); however, there was no difference in methane yield (g/kg DMI) or intensity (g/kg MS). Conclusion When cows are grazing high-quality spring pastures, there is no reduction in methane emission intensity when a concentrate pellet is fed. Implications The trend for an increase in methane production and the economic cost, must be considered when evaluating supplementary feeds/or feed additives as potential mitigation tools in pasture-based systems.