Effect of concentrate feeding level on methane emissions, production performance and rumen fermentation of Jersey cows grazing ryegrass pasture during spring

Dietary supplementation has been well documented as an effective enteric methane (CH4) mitigation strategy. However, limited studies have demonstrated the effect of concentrate level on enteric CH4 emissions from grazing dairy cows, and to our knowledge none of these studies included a pasture-only diet or reported on rumen fermentation measures. Sixty multiparous (4.0 ± 1.51 SD) Jersey cows, of which six were rumen-cannulated, were used in a randomised complete block design, and the cannulated cows were used in a separate replicated 3 × 3 Latin square design, to investigate the effect of concentrate supplementation (0, 4, and 8 kg/cow per day; as fed) on enteric CH4 emissions, milk production, dry matter intake (DMI), and rumen fermentation of dairy cows grazing perennial ryegrass pasture during spring, following a 14-d adaptation period. The sulphur hexafluoride tracer gas technique was used to measure enteric CH4 emissions from 10 cows of each treatment group over a single 9-d measurement period. Parallel with the CH4 measurement period, pasture DMI was determined using TiO2 and indigestible neutral detergent fibre as external and internal markers, respectively, while milk yield, milk composition, cow condition, and pasture pre- and post-grazing measurements were also recorded. Total DMI (13.4 to 18.0 kg/d), milk yield (12.9 to 19.2 kg/d), energy corrected milk (14.6 to 20.7 kg/d), milk lactose content (46.2 to 48.1 g/kg) and gross energy intake (239 to 316 MJ/d) increased, while milk fat content (50.0 to 44.2 g/kg) decreased with increasing concentrate feeding level. Volatile fatty acid concentrations and ruminal pH were mostly unaffected by treatment, while dry matter disappearance decreased and NH3-N concentration increased with increasing concentrate feeding level. Methane production (258 to 302 g/d) and CH4 yield (20.6 to 16.9 g/kg of DMI) were similar for all cows, while pasture DMI (13.4 to 10.8 kg/d) and CH4 intensity (20.4 to 15.9 g of CH4/kg of milk yield) decreased linearly with increasing concentrate feeding level. Results indicate that concentrate supplementation on high quality pasture-only diets have the potential to effectively reduce CH4 emissions per unit of milk yield from grazing cows during spring.