Long-term effect of linseed plus nitrate fed to dairy cows on enteric methane emission and nitrate and nitrite residuals in milk

Abstract

A previous study showed the additive methane (CH 4 )-mitigating effect of nitrate and linseed fed to non-lactating cows. Before practical application, the use of this new strategy in dairy cows requires further investigation in terms of persistency of methanogenesis reduction and absence of residuals in milk products. The objective of this experiment was to study the long-term effect of linseed plus nitrate on enteric CH 4 emission and performance in dairy cows. We also assessed the effect of this feeding strategy on the presence of nitrate residuals in milk products, total tract digestibility, nitrogen (N) balance and rumen fermentation. A total of 16 lactating Holstein cows were allocated to two groups in a randomised design conducted in parallel for 17 weeks. Diets were on a dry matter (DM) basis: (1) control (54% maize silage, 6% hay and 40% concentrate; CON) or (2) control plus 3.5% added fat from linseed and 1.8% nitrate (LIN + NIT). Diets were equivalent in terms of CP (16%), starch (28%) and NDF (33%), and were offered twice daily. Cows were fed ad libitum, except during weeks 5, 16 and 17 in which feed was restricted to 95% of dry matter intake (DMI) to ensure complete consumption of meals during measurement periods. Milk production and DMI were measured weekly. Nitrate and nitrite concentrations in milk and milk products were determined monthly. Daily CH 4 emission was quantified in open circuit respiration chambers (weeks 5 and 16). Total tract apparent digestibility, N balance and rumen fermentation parameters were determined in week 17. Daily DMI tended to be lower with LIN + NIT from week 4 to 16 (−5.1 kg/day on average). The LIN + NIT diet decreased milk production during 6 non-consecutive weeks (−2.5 kg/day on average). Nitrate or nitrite residuals were not detected in milk and associated products. The LIN + NIT diet reduced CH 4 emission to a similar extent at the beginning and end of the trial (−47%, g/day; −30%, g/kg DMI; −33%, g/kg fat-and protein-corrected milk, on average). Diets did not affect N efficiency and nutrients digestibility. In the rumen, LIN + NIT did not affect protozoa number but reduced total volatile fatty acid (−12%) and propionate (−31%) concentrations. We concluded that linseed plus nitrate may have a long-term CH 4 -mitigating effect in dairy cows and that consuming milk products from cows fed nitrate may be safe in terms of nitrate and nitrite residuals. Further work is required to optimise the doses of linseed plus nitrate to avoid reduced cows performance.

Low Emission Feed : using feed additives to decrease methane production in dairy cows

“…As protein is generally the most valuable milk component, an additive that decreases milk protein production may reduce interest in its adoption in practice. Guyader et al (2016) also reported reduced milk protein yield when a combination of nitrate and linseed was fed.…”

“…Aschenbach et al (2009) reported that nitrate impaired acetate uptake through the rumen wall in vitro. Nolan et al (2016) suggested this to be a possible explanation for a shift in VFA profile towards acetate that has been reported upon nitrate supplementation, both in vitro and in vivo (Zhou et al, 2012;Guyader et al, , 2016de Raphélis-Soissan et al, 2016a). However, in the study of Aschenbach et al (2009) only acetate uptake was measured, and not uptake of propionate and butyrate.…”

“…In the meta-analysis by Eugène et al (2008) Feeding nitrate is an example of an effective feed additive-based mitigation strategy that also may have some undesirable side effects. It is commonly agreed that feeding nitrate to ruminant animals decreases CH 4 production (see Van Zijderveld et al, 2011b;Guyader et al, , 2016Troy et al, 2015;Olijhoek et al, 2016). However, feeding nitrate imposes several restrictions on the formulation of the total diet.…”

“…In a follow-up study the effect of a combination of nitrate and linseed oil on enteric CH 4 production and nitrate and nitrite residuals in milk was compared to a control diet (Guyader et al, 2016). The combination of nitrate and linseed reduced CH 4 yield (-30%), but also reduced DMI (-13%), milk protein yield (-15%), total volatile fatty acid (-12%) and propionate (-31%) concentrations, which indicates that the applied doses (1.8% nitrate and 3.5% fat from linseed on a DM basis) where probably still too high to avoid adverse effects.…”

“…Guyader et al (2016) examined the effect of feeding nitrate and linseed on the presence of nitrate residuals in milk products during a 17-week experiment.…”