Discipline: environment; Keywords: methane mitigation, SF6, temperate pasture, urea.
There is not much information on the effect of dietary nitrate addition as a method to mitigate methane in grazing dairy cows. Therefore, the authors cited below did a study aiming to investigate the effect of nitrate addition on daily enteric methane emissions, production performance and rumen fermentation of multi-lactation Jersey cows grazing perennial ryegrass pasture, which contained about 7.3 g nitrate per kg dry matter (DM).
Thirty-two intact and 8 rumen-cannulated cows were subjected to a replicated 2 x 2 latin square design trial with 16 intact cow replicates and 4 rumen-cannulated cow replicates, supplemented with one of two concentrate supplements containing either urea (urea treatment), or urea (0.3)and nitrate (15.2g per kg DM) (nitrate treatment) as NPN source. The concentrate supplements were formulated to be iso-nitrogenous and iso-energetic, and were fed at a level of 5.4 kg DM per cow per day together with a strict daily herbage allowance of 14 kg DM per cow. The cows were gradually adapted to the concentrate supplement over 21 days. Daily enteric methane emissions of the cows were measured with the sulphur hexafluoride (SF6) 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 NDF respectively.
The total nitrate intake was respectively 5.2 and 9.7 g nitrate per kg DM for the urea and nitrate treatments. Total DMI (18.1 and 17.8 kg per day), milk yield (19.0 and 18 9 kg per cow per day) and daily methane emissions (400 and 405 g per day) were unaffected by treatment. Total milk solids (135 and 133 g per kg), milk lactose (47.3 and 46.7 g per kg) and MUN (12.6 and 11.6 mg per dL) were higher for the nitrate group. Rumen fermentation parameters such as VFA 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 treatment.
In conclusion: Dietary nitrate supplementation, in contrast to hypothesis, was not an effective enteric methane emission suppressor, at least in cows grazing perennial ryegrass. However, the unforeseen high nitrate content of the grazed pasture resulting in a comparatively small margin in total nitrate intake between the urea and nitrate treatment could have been a contributing factor.
Van Wyngaard, J.D.V., Meeske, R. & Erasmus, L.J., 2019. Effect of dietary nitrate on enteric methane emissions, production performance and rumen fermentation of dairy cows grazing ryegrass pasture during spring. Anim. Fd. Sc. & Techn. 252, 64-73.