Effect of dietary nitrate on enteric methane emissions, production performance and rumen fermentation of dairy cows grazing ryegrass pasture during spring

• Published in: Animal feed science and technology 2019-06, Vol.252, p.64-73
• Main Authors: van Wyngaard, J.D.V., Meeske, R., Erasmus, L.J.
• Format: Article
• Language: English
• Subjects: Electron receptor; Methane mitigation; SF6; Temperate pasture; Urea
• ISSN: 0377-8401; 1873-2216
• DOI: 10.1016/j.anifeedsci.2019.04.006

•Dietary nitrate was supplemented to dairy cows grazing ryegrass pasture.•Milk yield, total DMI and pasture DMI was unaffected by treatment.•Methane emissions were unaffected by treatment.•Rumen fermentation parameters were unaffected by treatment.•Lack of treatment response could be due to high nitrate levels in pasture. Limited studies investigated the effect of dietary nitrate addition as methane (CH4) mitigation strategy for dairy cows grazing pasture. This study aimed to investigate the effect of dietary nitrate addition on daily enteric CH4 emissions, production performance and rumen fermentation of multiparous Jersey cows grazing perennial ryegrass pasture (containing approximately 7.3 g of nitrate/kg of dry matter (DM)). Thirty-two intact and eight rumen-cannulated multiparous Jersey cows were subjected to a replicated 2 × 2 Latin square design with 16 intact cow replicates and four rumen-cannulated cow replicates supplemented with one of two concentrates containing either urea (urea treatment), or urea and nitrate (nitrate treatment) as nonprotein nitrogen source (NPN; containing 0.3 and 15.2 g of nitrate/kg of DM, respectively). Concentrates were formulated to be isonitrogenous and isoenergetic, and was fed at 5.4 kg of DM/cow per d along with a strict daily herbage allowance of 14 kg of DM/cow. Cows were gradually adapted to concentrates over a 3-wk period. Total nitrate intake was 5.2 and 9.7 g of nitrate/kg of DM for the urea and nitrate treatment groups, respectively. Daily enteric CH4 emissions of 28 cows were measured with the sulphur hexafluoride tracer gas technique for six consecutive days during each experimental period with parallel total DM intake (DMI) estimates. Pasture DMI was calculated from faecal output and pasture digestibility using TiO2 and indigestible neutral detergent, respectively. Total DMI (18.1 and 17.8 kg/d), milk yield (19.0 and 18.9 kg/cow per d) and daily CH4 emissions (400 and 405 g/d) were unaffected by dietary treatment for the urea and nitrate group, respectively. Total milk solids content (135 vs. 133 g/kg), milk lactose content (47.3 vs. 46.7 g/kg) and milk urea nitrogen concentration (MUN; 12.6 vs. 11.6 mg/dL) were higher for the nitrate group. Rumen fermentation parameters such as volatile fatty acid profile, ammonium nitrogen, and DM and fibre disappearance were unaffected by treatment. Minor effects on ruminal pH were observed with an increasing tendency towards the nitrate group. In this study, dietary n