Use of nitrate and Propionibacterium acidipropionici to reduce methane emissions and increase wool growth of Merino sheep

Abstract

The effects of dietary nitrate and of Propionibacterium acidipropionici (PA) on methane and nitrous oxide emissions, methaemoglobinaemia, volatile fatty acid (VFA) concentration and productivity of sheep were studied. It was hypothesised that PA supplementation would increase the rate of nitrite reduction to ammonia in the rumen and therefore reduce risks of methaemoglobinaemia. Fine-wool Merino wethers (n = 28; 31.8 ± 3.7 kg; 11 months of age) were acclimated to four isonitrogenous and isoenergetic diets based on oaten chaff (1.0 kg/day) supplemented with either urea (1.1% of DM; T1 and T2) or a nitrate source (2.0% of DM; T3 and T4) while T2 and T4 were also supplemented with PA (11.5 × 1010 CFU/day). Replacing urea with nitrate lowered methane production (g/day) by 19% and methane yield (g/kg DMI) by 15%, improved clean wool growth by 12% (P < 0.001) and tended to increase skin temperature (P < 0.1). Nitrate increased ruminal acetate to propionate ratio by 27%, increased plasma nitrite and nitrate concentrations and blood methaemoglobin (MetHb) level up to 45% of total haemoglobin. Nitrous oxide emission from sheep confined in respiration chambers was higher (P < 0.001) when nitrate was fed, lowering the net benefit of methane mitigation on global warming potential (CO2 equivalents/kg DMI) by 18%. In contrast, PA had little effect, decreasing total VFA concentration (P < 0.05), increasing rumen pH (P < 0.05) and clean wool growth (P < 0.05) of urea-fed sheep. This study confirmed the beneficial effects of nitrate on net greenhouse gas reduction and wool growth, but showed that methaemoglobinaemia risks may be higher when diets are fed at a restricted level and contain only low levels of readily fermented carbohydrate. PA supplementation was not effective in reducing methaemoglobinaemia, but did increase clean wool growth of urea-fed sheep.

Dietary Nitrate for Methane Mitigation Leads to Nitrous Oxide Emissions from Dairy Cows

“…Higher levels of 10 to 20 mg N 2 O head −1 h −1 were reported for lactating dairy cows (Hamilton et al, 2010) and for feedlot steers and calves (Stackhouse et al, 2011). And in a recent study, de Raphélis‐Soissan et al (2014) reported that respiration chambers with sheep fed NO 3 − instead of urea had higher N 2 O emissions, thus lowering the GHG mitigation effect of CH 4 by 18%. These studies were all conducted with respiration chambers and the source(s) of N 2 O unknown.…”

Cattle Diets Strongly Affect Nitrous Oxide in the Rumen

“…as major pathway and secondly, possibly being quantitatively less important, NO 3 − and NO 2 − being toxic to methanogens in the rumen. In both cases, CH 4 production was decreased by addition of nitrate, however, de Raphélis-Soissan et al [46] stated that, on the other hand, the N 2 O emission from sheep in respiration chambers was increased which led to a reduction of the net benefit of methane mitigation on global warming potential (CO 2 equivalents/kg DMI) of 18%. This effect could be mitigated by using encapsulated NO 3 − as slow-release form, thereby lowering NO 2 − toxicity after nitrate ingestion [11].…”

“…However, only traces were found under those experimental feeding conditions with addition of nitrate. Also de Raphélis-Soissan et al [46] and Lee et al [11] fed nitrate to ruminants in an attempt to lower ruminal CH 4 production. In this regard, two main possibilities by which NO 3 − reduces enteric CH 4 production were discussed [11]: NO 3 − reduction (thermodynamically favorable in comparison to methanogenesis)…”

“…However, the possibility of N 2 O formation in the oral cavity can be excluded for the current study as the gas samples were taken directly from the rumen atmosphere without oral contact. Also, feces as a possible source of N 2 O as discussed for sheep [46] can be excluded in our study due to the sampling method. As enteric formation under anaerobic conditions seems unlikely, the transfer from the forage into the rumen is the most likely way.…”

Nitrato na dieta de ruminantes como estratégia nutricional para mitigação de metano entérico

“…Como em outros estudos ( VAN ZIJDERVELD et al, 2010;RAPHÉLIS-SOISSAN et al, 2014;GUYADER et al, 2015;LEE et al, 2015a) alimentos concentrados o pico de produção é 2 a 3 horas após a ingestão e para alimentos volumoso 4 a 5 horas. Contudo, neste experimento a menor proporção de acetato (mol %), em ambas as dietas foi observada 4 horas após a alimentação coincidindo, com a redução no pH…”