Effectiveness of nitrate addition and increased oil content as methane mitigation strategies for beef cattle fed two contrasting basal diets1

Abstract

The objectives of this study were to investigate the effects of (1) the addition of nitrate and (2) an increase in dietary oil on methane (CH4) and hydrogen (H2) emissions from 2 breeds (cross-bred Charolais and purebred Luing) of finishing beef cattle receiving 2 contrasting basal diets consisting (grams per kilogram DM) of 500:500 (Mixed) and 80:920 (Concentrate) forage to concentrate ratios. Within each basal diet there were 3 treatments: (i) control treatments (mixed-CTL and concentrate-CTL) contained rapeseed meal as the protein source, which was replaced with either (ii) calcium nitrate (mixed-NIT and concentrate-NIT) supplying 21.5 g nitrate/kg DM, or (iii) rapeseed cake (mixed-RSC and concentrate-RSC) to increase dietary oil from 27 (CTL) to 53 g/kg DM (RSC). Following adaption to diets, CH4 and H2 emissions were measured on 1 occasion from each of the 76 steers over a 13-wk period. Dry matter intakes tended (P = 0.051) to be greater for the concentrate diet than the mixed diet; however, when expressed as grams DMI per kilogram BW, there was no difference between diets (P = 0.41). Dry matter intakes for NIT or RSC did not differ from CTL. Steers fed a concentrate diet produced less CH4 and H2 than those fed a mixed diet (P < 0.001). Molar proportions of acetate (P < 0.001) and butyrate (P < 0.01) were lower and propionate (P < 0.001) and valerate (P < 0.05) higher in the rumen fluid from steers fed the concentrate diet. For the mixed diet, CH4 yield (grams per kilogram DMI) was decreased by 17% when nitrate was added (P < 0.01), while H2 yield increased by 160% (P < 0.001). The addition of RSC to the mixed diet decreased CH4 yield by 7.5% (P = 0.18). However, for the concentrate diet neither addition of nitrate (P = 0.65) nor increasing dietary oil content (P = 0.46) decreased CH4 yield compared to concentrate-CTL. Molar proportions of acetate were higher (P < 0.001) and those of propionate lower (P < 0.01) in rumen fluid from NIT treatments compared to respective CTL treatments. Overall, reductions in CH4 emissions from adding nitrate or increasing the oil content of the mixed diet were similar to those expected from previous reports. However, the lack of an effect of these mitigation strategies when used with high concentrate diets has not been previously reported. This study shows that the effect of CH4 mitigation strategies is basal diet-dependent.

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

“…reduced energy loss) from steers offered the Mixed diet (Troy et al, 2015); however no response was observed in the present study on FCR or RFI. The benefits in reduced energy loss as CH 4 observed by Troy et al (2015) may have been counterbalanced by sub-clinical effects of nitrate. In contrast, nitrate improved the FCR of steers offered the Concentrate diet, but with no aligned reduction in CH 4 (Troy et al, 2015).…”

“…In the present study, steers offered a higher proportion of concentrate in the diet expressed better feed efficiency (RFI) than those offered a mixed forage : concentrate diet. These steers were also shown to have lower levels of CH 4 production compared to steers offered higher quantities of forage (Troy et al, 2015).…”

“…However, since the AHEE level in the RSC treatment was only 48 g/kg DM this dietary lipid concentration did not suppress DMI and no adverse effects were observed for any performance or carcass-related trait. The RSC treatment was shown to positively reduce CH 4 production by 7.5% from steers offered the Mixed basal diet but no reduction in CH 4 was observed on the Concentrate diet (Troy et al, 2015).…”

“…For all steers, ultrasonic fat depth was obtained at the 12th/13th rib at the start (FD0) and end (FD1) of the Pre-slaughter measurements and carcass quality Steers remained within the same pens and on the same diets from the end of the 56-day test to slaughter. During this period CH 4 measurements were obtained from 76 of these steers and reported in Troy et al (2015). On the day before slaughter, ultrasonic fat depth (FD2) at the 12th/13th rib was measured in all steers as described above.…”

“…The benefits in reduced energy loss as CH 4 observed by Troy et al (2015) may have been counterbalanced by sub-clinical effects of nitrate. In contrast, nitrate improved the FCR of steers offered the Concentrate diet, but with no aligned reduction in CH 4 (Troy et al, 2015).…”