Persistency of methane mitigation by dietary nitrate supplementation in dairy cows

Abstract

Feeding nitrate to dairy cows may lower ruminal methane production by competing for reducing equivalents with methanogenesis. Twenty lactating Holstein-Friesian dairy cows (33.2±6.0 kg of milk/d; 104±58 d in milk at the start of the experiment) were fed a total mixed ration (corn silage-based; forage to concentrate ratio 66:34), containing either a dietary urea or a dietary nitrate source [21 g of nitrate/kg of dry matter (DM)] during 4 successive 24-d periods, to assess the methane-mitigating potential of dietary nitrate and its persistency. The study was conducted as paired comparisons in a randomized design with repeated measurements. Cows were blocked by parity, lactation stage, and milk production at the start of the experiment. A 4-wk adaptation period allowed the rumen microbes to adapt to dietary urea and nitrate. Diets were isoenergetic and isonitrogenous. Methane production, energy balance, and diet digestibility were measured in open-circuit indirect calorimetry chambers. Cows were limit-fed during measurements. Nitrate persistently decreased methane production by 16%, whether expressed in grams per day, grams per kilogram of dry matter intake (DMI), or as percentage of gross energy intake, which was sustained for the full experimental period (mean 368 vs. 310±12.5 g/d; 19.4 vs. 16.2±0.47 g/kg of DMI; 5.9 vs.4.9±0.15% of gross energy intake for urea vs. nitrate, respectively). This decrease was smaller than the stoichiometrical methane mitigation potential of nitrate (full potential=28% methane reduction). The decreased energy loss from methane resulted in an improved conversion of dietary energy intake into metabolizable energy (57.3 vs. 58.6±0.70%, urea vs. nitrate, respectively). Despite this, milk energy output or energy retention was not affected by dietary nitrate. Nitrate did not affect milk yield or apparent digestibility of crude fat, neutral detergent fiber, and starch. Milk protein content (3.21 vs. 3.05±0.058%, urea vs. nitrate respectively) but not protein yield was lower for dietary nitrate. Hydrogen production between morning and afternoon milking was measured during the last experimental period. Cows fed nitrate emitted more hydrogen. Cows fed nitrate displayed higher blood methemoglobin levels (0.5 vs. 4.0±1.07% of hemoglobin, urea vs. nitrate respectively) and lower hemoglobin levels (7.1 vs. 6.3±0.11 mmol/L, urea vs. nitrate respectively). Dietary nitrate persistently decreased methane production from lactating dairy cows fed restricted amounts of feed, but the reduction in energy losses did not improve milk production or energy balance.

Impact of adding nitrate or increasing the lipid content of two contrasting diets on blood methaemoglobin and performance of two breeds of finishing beef steers

“…No individual MetHb measurement was >15% of total Hb which was substantially <30% total Hb, the value associated with clinical symptoms of methaemoglobinemia (Bruning-Fann and Kaneene, 1993). This agrees with most studies in which animals were adapted slowly to dietary nitrate by increasing nitrate intakes over a period of weeks (cattle:, Hulshof et al, 2012;Van Zijderveld et al, 2011 andsheep: Li et al, 2012;Van Zijderveld et al, 2010). Slow adaptation to dietary nitrate allows the rate of reduction of nitrite to ammonia by the rumen microflora to increase and prevents accumulation of nitrite in the rumen and absorption from the rumen and thereby avoids conversion of haemoglobin to MetHb (Lee and Beauchemin, 2014).…”

“…Consistent results in the literature demonstrate, over the short-term, that dietary nitrate can be successfully administered at levels capable of reducing CH 4 with no adverse effects on performance in sheep (Van Zijderveld et al, 2010;Li et al, 2012;El-Zaiat et al, 2014), goats (Nguyen et al, 2010), dairy cows (Van Zijderveld et al, 2011) and beef cattle (Huyen et al, 2010). However, a comprehensive review by Bruning-Fann and Kaneene (1993) reported a reduction in feed intake when nitrate was included in the diet at 10 g nitrate/kg DM (cattle) and 30 g nitrate/kg DM (sheep).…”

“…Furthermore, the Nitrate treatment tended to improve FCR of steers offered the Concentrate basal diet but not the Mixed diet. Van Zijderveld et al (2011) reported the persistency of the effects of dietary nitrate in dairy cows fed a mixed forage and concentrate diet, in which measurements were obtained over four successive 24-day periods. No adverse effects on milk yield or energy balance were identified, but the reductions in energy losses as CH 4 were not associated with any improvements in productivity.…”

Technical options for the mitigation of direct methane and nitrous oxide emissions from livestock: a review

“…Decreasing dietary protein concentration to address NH 3 and N 2 O losses from stored manure or manure-amended soil may increase enteric CH 4 emissions, as shown by the modelling work of Dijkstra et al (2011b). Low-protein diets for ruminants should be balanced for ruminally degradable protein in order to not impair microbial protein synthesis and fibre degradability in the rumen.…”

“…Recent research on sheep (Sar et al, 2004;Nolan et al, 2010;van Zijderveld et al, 2010) and cattle (van Zijderveld et al, 2011a and2011b;Hulshof et al, 2012) has shown promising results with nitrates decreasing enteric CH 4 production by up to 50%. Nitrates may be particularly attractive in developing countries where forages contain negligible levels of nitrate and insufficient CP for maintaining animal production.…”