Sulfur Hexafluoride Tracer Gas Technique Research Articles

Effect of combining the methanogenesis inhibitor 3-nitrooxypropanol and cottonseeds on methane emissions, feed intake, and milk production of grazing dairy cows

No single enteric CH4 mitigating strategy has been consistently effective or is readily applicable to ruminants in grassland systems. When CH4 mitigating strategies are effective under grazing conditions, mitigation is mild to moderate at best. A study was conducted to evaluate the potential of combining two CH4 mitigation strategies deemed feasible to apply in grazing dairy cows, the methanogenesis inhibitor 3-nitrooxypropanol additive (3-NOP) and cottonseed supplementation (CTS), seeking to enhance their individual CH4 mitigating potential. Forty-eight dairy cows were evaluated in a continuous grazing study and supplemented with either a starch-based concentrate (STA) or one that contained cottonseeds (1.75 kg DM/d; CTS), and with either 19 g/d of 10% 3-NOP (Bovaer®) or the additive’s carrier (placebo), in a 2 × 2 factorial arrangement of treatments. Treatments were supplied mixed with a concentrate supplement (5 kg/d as fed) and offered in two equal rations at milking. Methane emissions were measured on weeks 4 and 8 using the sulphur hexafluoride tracer gas technique over a 5-d period. The 3-NOP and CTS treatments tended to interact on absolute CH4 such that 3-NOP decreased CH4 by 13.4% with STA, but there was no mitigation with 3-NOP and CTS. Treatment interactions were also obtained for CH4 yield, where 3-NOP tended to decrease CH4 when supplied with STA, and tended to increase it with CTS. The increase in CH4 yield with the CTS diet was driven by a numerical decrease in DM intake. Methane intensity was not affected by the 3-NOP or CTS treatments. Total volatile fatty acids in ruminal fluid were not affected by 3-NOP supplementation, but a reduction in acetate and an increase in propionate proportion occurred, resulting in decreased acetate: propionate. The 3-NOP additive decreased grass intake; however, energy−corrected milk yield and milk composition were largely unaffected. Milk urea increased with 3-NOP supplementation. Combining twice daily supplementation of 3-NOP and CTS did not enhance their CH4 mitigation potential when fed to grazing dairy cows. The relatively low inhibition of CH4 production by 3-NOP compared to studies with total mixed rations may result from the mode of delivery (pulse dosed twice daily) and time gap caused by experimental handling and moving of animals to pasture after 3-NOP supplementation in the milking parlour, which could have impaired the synchrony between the additive presence in the rumen and grass intake in paddocks.

Phenotypic association among performance, feed efficiency and methane emission traits in Nellore cattle.

Enteric methane (CH4) emissions are a natural process in ruminants and can result in up to 12% of energy losses. Hence, decreasing enteric CH4 production constitutes an important step towards improving the feed efficiency of Brazilian cattle herds. The aim of this study was to evaluate the relationship between performance, residual feed intake (RFI), and enteric CH4 emission in growing Nellore cattle (Bos indicus). Performance, RFI and CH4 emission data were obtained from 489 animals participating in selection programs (mid-test age and body weight: 414±159 days and 356±135 kg, respectively) that were evaluated in 12 performance tests carried out in individual pens (n = 95) or collective paddocks (n = 394) equipped with electronic feed bunks. The sulfur hexafluoride tracer gas technique was used to measure daily CH4 emissions. The following variables were estimated: CH4 emission rate (g/day), residual methane emission and emission expressed per mid-test body weight, metabolic body weight, dry matter intake (CH4/DMI), average daily gain, and ingested gross energy (CH4/GE). Animals classified as negative RFI (RFI<0), i.e., more efficient animals, consumed less dry matter (P <0.0001) and emitted less g CH4/day (P = 0.0022) than positive RFI animals (RFI>0). Nonetheless, more efficient animals emitted more CH4/DMI and CH4/GE (P < 0.0001), suggesting that the difference in daily intake between animals is a determinant factor for the difference in daily enteric CH4 emissions. In addition, animals classified as negative RFI emitted less CH4 per kg mid-test weight and metabolic weight (P = 0.0096 and P = 0.0033, respectively), i.e., most efficient animals could emit less CH4 per kg of carcass. In conclusion, more efficient animals produced less methane when expressed as g/day and per kg mid-test weight than less efficient animals, suggesting lower emissions per kg of carcass produced. However, it is not possible to state that feed efficiency has a direct effect on enteric CH4 emissions since emissions per kg of consumed dry matter and the percentage of gross energy lost as CH4 are higher for more efficient animals.

Performance, nutrient use, and methanogenesis of Nellore cattle on a continuous grazing system of Urochloa brizantha and fed supplement types varying on protein and energy sources

Supplementation of grazing cattle may improve forage utilization, methane emission and efficiency of nutrients use. This study aimed to evaluate the effect of different supllementation strategies on performance, metabolic parameters and methane emission in Nellore cattle reared on well-managed marandu palisadegrass (Urochloa brizantha cv Marandu) pastures. Three supplementation strategies consisted of protein and energy sources from traditional ingredients compared to a novel feedstuff: TS) Traditional supplement (protein-energy) composed of ground corn and soybean meal; ES) energy supplement composed of ground corn; and DS) Distiller's coproduct supplement (protein-energy) composed of ground corn and dried distiller grain (DDG). All supplements were offered at 0.3% of body weight (BW). Sixty-nine growing Nellore bulls [251 kg of body weight (BW) ± 13.0 kg] were randomly distributed according to initial BW in nine paddocks (twenty-three animals per treatment, three paddocks per treatment) to evaluate liveweight gain. From these, eighteen bulls (381.83 kg BW ± 16.15 kg) were selected for methane emission measurements (six animals per treatment) using sulfur hexafluoride tracer gas technique. Six rumen cannulated steers (289.5 kg BW ± 19.6 kg) across six paddocks (two per treatment) were used in an incomplete double Latin square design (3 treatments x 4 periods) to evaluate metabolic parameters. Statistical analyses were done using the Mixed Procedure in SAS and adopting significance level at 5%. It was hypothesized that the use of DS or ES, could increase the N use efficiency because of a higher rumen undegradable protein content, and more energy available for microbial synthesis in the rumen, respectively. Overall, there were no differences on animal performance, intake, nutrients digestibility, ruminal parameters, and microbial protein synthesis among treatments indicating that any of the supplemental sources could be utilized. Although, animals in DS had lower urine N excretion. The ES supplement increased methane yield (g/DMI) and the methane conversion factor Ym (% of gross energy intake) when compared to other treatments, but not methane production, which was similar among all treatments.

Effect of tannin-containing hays on enteric methane emissions and nitrogen partitioning in beef cattle1.

The objective of this study was to determine whether feeding tannin-containing hays to heifers and mature beef cows influences enteric methane (CH4) emissions and nitrogen (N) excretion relative to feeding traditional legume and grass hays. Fifteen mature beef cows (Exp. 1) and 9 yearling heifers (Exp. 2) were each randomly assigned to treatment groups in an incomplete bock design with 2 periods and 6 types of hays with 3 hays fed each period (n = 5 cows and 3 heifers per treatment). Groups were fed tannin-containing [birdsfoot trefoil (BFT), sainfoin (SAN), small burnet (SML)] or non-tannin-containing [alfalfa (ALF), cicer milkvetch (CMV), meadow bromegrass (MB)] hays. Each period consisted of 14 d of adjustment followed by 5 d of sample collection. Nine cows and 9 heifers were selected for the measurement of enteric CH4 emissions (sulfur hexafluoride tracer gas technique), and excretion of feces and urine, while dry matter intake (DMI) was measured for all animals. The concentration of condensed tannins in SAN and BFT was 2.5 ± 0.50% and 0.6 ± 0.09% of dry matter (DM), respectively, while SML contained hydrolyzable tannins (4.5 ± 0.55% of DM). Cows and heifers fed tannin-containing hays excreted less urinary urea N (g/d; P < 0.001) and showed lower concentrations of blood urea N (mg/dL; P < 0.001) than animals fed ALF or CMV, indicating that tannins led to a shift in route of N excretion from urine to feces. Additionally, cows fed either BFT or CMV showed the greatest percentage of retained N (P < 0.001). Enteric CH4 yield (g/kg of DMI) from heifers (P = 0.089) was greatest for MB, while daily CH4 production (g/d) from heifers (P = 0.054) was least for SML. However, digestibility of crude protein was reduced for cows (P < 0.001) and heifers (P < 0.001) consuming SML. The results suggest that tannin-containing hays have the potential to reduce urinary urea N excretion, increase N retention, and reduce enteric CH4 emissions from beef cattle. The non-bloating tannin-free legume CMV may also reduce environmental impacts relative to ALF and MB hays by reducing N excretion in urine and increasing N retention.

Effect of dietary nitrate on enteric methane emissions, production performance and rumen fermentation of dairy cows grazing ryegrass pasture during spring

Limited studies investigated the effect of dietary nitrate addition as methane (CH4) mitigation strategy for dairy cows grazing pasture. This study aimed to investigate the effect of dietary nitrate addition on daily enteric CH4 emissions, production performance and rumen fermentation of multiparous Jersey cows grazing perennial ryegrass pasture (containing approximately 7.3 g of nitrate/kg of dry matter (DM)). Thirty-two intact and eight rumen-cannulated multiparous Jersey cows were subjected to a replicated 2 × 2 Latin square design with 16 intact cow replicates and four rumen-cannulated cow replicates supplemented with one of two concentrates containing either urea (urea treatment), or urea and nitrate (nitrate treatment) as nonprotein nitrogen source (NPN; containing 0.3 and 15.2 g of nitrate/kg of DM, respectively). Concentrates were formulated to be isonitrogenous and isoenergetic, and was fed at 5.4 kg of DM/cow per d along with a strict daily herbage allowance of 14 kg of DM/cow. Cows were gradually adapted to concentrates over a 3-wk period. Total nitrate intake was 5.2 and 9.7 g of nitrate/kg of DM for the urea and nitrate treatment groups, respectively. Daily enteric CH4 emissions of 28 cows were measured with the sulphur hexafluoride 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 neutral detergent, respectively. Total DMI (18.1 and 17.8 kg/d), milk yield (19.0 and 18.9 kg/cow per d) and daily CH4 emissions (400 and 405 g/d) were unaffected by dietary treatment for the urea and nitrate group, respectively. Total milk solids content (135 vs. 133 g/kg), milk lactose content (47.3 vs. 46.7 g/kg) and milk urea nitrogen concentration (MUN; 12.6 vs. 11.6 mg/dL) were higher for the nitrate group. Rumen fermentation parameters such as volatile fatty acid 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 group. In this study, dietary nitrate supplementation was not an effective CH4 mitigation strategy for dairy cows grazing perennial ryegrass. This can be ascribed to the unforeseen high nitrate content of the grazed pasture causing a relative small margin in total nitrate intake between the urea and nitrate treatment diets.

Effect of concentrate level on enteric methane emissions, production performance, and rumen fermentation of Jersey cows grazing kikuyu-dominant pasture during summer

The effect of concentrate feeding level on enteric CH4 emissions from cows grazing medium quality summer pasture is yet to be investigated. Sixty multiparous Jersey cows (9 rumen-cannulated) were used in a randomized complete block design study (with the cannulated cows in a 3 × 3 Latin square design) to investigate the effect of concentrate feeding level (0, 4, and 8 kg/cow per day; as-fed basis) on enteric CH4 emissions, production performance, and rumen fermentation of dairy cows grazing summer pasture (17 cows plus 3 cannulated cows per treatment). Enteric CH4 emissions were measured from 11 cows per treatment group during one 7-d measurement period using the sulfur hexafluoride tracer gas technique. Pasture dry matter intake (DMI) was determined parallel with the CH4 measurement period using TiO2 as an external marker, and milk yield, milk composition, cow condition, and pasture pre- and postgrazing measurements were also recorded. Daily total DMI (11.2 to 15.6 kg/cow), milk yield (9.1 to 18.2 kg/cow), energy-corrected milk (ECM; 11.2 to 21.6 kg/cow), and milk lactose content (44.1 to 46.7 g/kg) increased linearly, whereas pasture DMI (11.2 to 8.4 kg/cow) decreased linearly with increasing concentrate feeding level. Daily CH4 production (323 to 378 g/d) increased linearly due to the increase in total DMI, whereas CH4 yield (29.1 to 25.1 g/kg of DMI) and CH4 intensity (35.5 to 21.1 g/kg of milk yield; and 28.8 to 17.6 g/kg of ECM) decreased linearly with increasing concentrate feeding level. Diurnal ruminal pH (6.45 to 6.32) and in sacco DM and neutral detergent fiber disappearance decreased linearly. Acetic and propionic acid were unaffected by treatment, whereas butyric acid (5.21 to 6.14 mM) increased linearly and quadratically with increasing concentrate feeding level. It was concluded that a high concentrate feeding level not only increases animal efficiency but is moreover a viable CH4 mitigation option for dairy cows grazing kikuyu-dominant pasture in late summer when pasture is inherently fibrous.

Effect of dietary nitrate on enteric methane emissions, production performance and rumen fermentation of dairy cows grazing kikuyu-dominant pasture during summer

Dietary nitrate supplementation is an effective methane (CH4) mitigation strategy in total mixed ration based diets fed to ruminants. To date, limited information is available on the effect of dietary nitrate on CH4 production from grazing dairy cows. Fifty-four multiparous Jersey cows were subjected to a randomised complete block design (blocked according to milk yield, days in milk and parity) to evaluate the effect of three dietary nitrate levels on enteric CH4 emissions and cow production performance. Additionally, six rumen-cannulated cows in a replicated 3 × 3 Latin square design were used in a rumen study. Dietary treatments consisted of concentrate fed at 5.4 kg of DM/cow per day containing one of three levels of dietary nitrate: 0 g (control), 11 g (low nitrate), and 23 g of nitrate/kg of dry matter (DM; high nitrate). Cows grazed late-summer pasture containing approximately 3 g of nitrate/kg of DM. Concentrates were formulated to be isonitrogenous, by substituting urea, and isoenergetic. Cows were gradually adapted to concentrates over a 3-wk period before the onset of a 57-d experimental period. Enteric CH4 emissions and total dry matter intake (DMI) from 11 cows per treatment were measured during one 6-d measurement period using the sulphur hexafluoride tracer gas technique. Individual pasture DMI was determined using TiO2 and indigestible neutral detergent fibre (NDF). Milk yield decreased by approximately 12% when feeding the high nitrate diet compared with the control and low nitrate diets. Although total DMI was unaffected by treatment, concentrate DMI decreased linearly (5.5–3.7 kg/d) while pasture DMI increased linearly (9.1–11.4 kg/d) with increasing dietary nitrate addition. Methane production (313–280 g/d), CH4 yield (21.8–18.7 g/kg of DMI) and CH4 energy per gross energy intake (6.9–5.9%) tended to decrease linearly with increasing dietary nitrate addition. Diurnal ruminal pH of the high nitrate group was greater, for selective periods after concentrate feeding, than the control and low nitrate groups. Spot sample ruminal pH (6.2–6.3) tended to increase while total volatile fatty acid (VFA) concentration (99.9–104 mM/L) increased quadratically with increasing dietary nitrate addition. Individual VFA concentrations were unaffected by treatment. Rate of NDF disappearance (2.4–2.8%/h) after 18 h of ruminal incubation tended to increase quadratically with increasing dietary nitrate addition. Dietary nitrate fed to grazing dairy cows tended to decrease CH4 emissions while improving the fibrolytic environment of the rumen. However, when feeding high levels of dietary nitrate a decrease in milk yield could be expected due to a decrease in concentrate DMI.

Effect of concentrate feeding level on methane emissions, production performance and rumen fermentation of Jersey cows grazing ryegrass pasture during spring

Dietary supplementation has been well documented as an effective enteric methane (CH4) mitigation strategy. However, limited studies have demonstrated the effect of concentrate level on enteric CH4 emissions from grazing dairy cows, and to our knowledge none of these studies included a pasture-only diet or reported on rumen fermentation measures. Sixty multiparous (4.0 ± 1.51 SD) Jersey cows, of which six were rumen-cannulated, were used in a randomised complete block design, and the cannulated cows were used in a separate replicated 3 × 3 Latin square design, to investigate the effect of concentrate supplementation (0, 4, and 8 kg/cow per day; as fed) on enteric CH4 emissions, milk production, dry matter intake (DMI), and rumen fermentation of dairy cows grazing perennial ryegrass pasture during spring, following a 14-d adaptation period. The sulphur hexafluoride tracer gas technique was used to measure enteric CH4 emissions from 10 cows of each treatment group over a single 9-d measurement period. Parallel with the CH4 measurement period, pasture DMI was determined using TiO2 and indigestible neutral detergent fibre as external and internal markers, respectively, while milk yield, milk composition, cow condition, and pasture pre- and post-grazing measurements were also recorded. Total DMI (13.4 to 18.0 kg/d), milk yield (12.9 to 19.2 kg/d), energy corrected milk (14.6 to 20.7 kg/d), milk lactose content (46.2 to 48.1 g/kg) and gross energy intake (239 to 316 MJ/d) increased, while milk fat content (50.0 to 44.2 g/kg) decreased with increasing concentrate feeding level. Volatile fatty acid concentrations and ruminal pH were mostly unaffected by treatment, while dry matter disappearance decreased and NH3-N concentration increased with increasing concentrate feeding level. Methane production (258 to 302 g/d) and CH4 yield (20.6 to 16.9 g/kg of DMI) were similar for all cows, while pasture DMI (13.4 to 10.8 kg/d) and CH4 intensity (20.4 to 15.9 g of CH4/kg of milk yield) decreased linearly with increasing concentrate feeding level. Results indicate that concentrate supplementation on high quality pasture-only diets have the potential to effectively reduce CH4 emissions per unit of milk yield from grazing cows during spring.

Technical note: A simple back-mounted harness for grazing dairy cows to facilitate the sulfur hexafluoride tracer gas technique

We describe here a cattle harness to attach a gas collection vessel to facilitate the sulfur hexafluoride (SF6) tracer gas technique. The harness consists of 2 major components: (1) a lightweight, robust body fabricated from an equine surcingle or lunge roller with padded thoracic trapezius pressure points, a bespoke shaping shaft for spine support, and adjustable buckles on both sides; and (2) an elastic flank-strap to prevent the harness from dislodging. The spine support consists of stainless steel laminated with carbon fiber. This support minimizes the contact area with the animal's skin, relieves the spine area of pressure, and creates free flow of ambient air below the platform, reducing sweat accumulation and hence preventing skin lesions. The harness weighs approximately 1.2 kg, allows for attachment of 2 gas collection vessels (animal and background sample), and is cost effective.

The effects of supplementing Acacia mearnsii tannin extract on dairy cow dry matter intake, milk production, and methane emission in a tropical pasture.

The study assessed the effect of Acacia mearnsii tannin extract supplementation grazing dairy cows on dry matter (DM) intake, enteric methane (CH4) emission, and performance. Twelve Holstein cows were divided into two groups and subjected to two treatments that consisted of millet pasture (Pennisetum glaucum L.) plus supplementation with 6kg of concentrate (750-g/kg ground corn and 250-g/kg soybean meal) including or excluding 120-g tannin extract. The trial design was a double reversal using three periods of 28days each, with 21days for the adaption period, and 7days for sample collection. Herbage intake was measured using the n-alkane technique, and daily CH4 emission was measured with the sulfur hexafluoride tracer gas technique. Individual total DM intake (mean=17.1kg/day), herbage DM intake (mean=11.8kg/day), and milk production (mean=19.2kg/day) were similar between treatments. CH4 emission significantly decreased (32%, P<0.05) in the animals supplemented with tannin extract, compared to non-supplemented animals. On the other hand, as proportion of DM intake or milk production, methane emission tended to decrease in tannin-supplemented animals. Supplementing dairy cows grazing a millet pasture with 120-g tannin extract reduced daily CH4 emission without affecting animal performance.

Feed efficiency and enteric methane production of Nellore cattle in the feedlot and on pasture

The objective of the present study was to assess the relationship between residual feed intake (RFI) evaluated in a feedlot-performance test and on pasture, and to determine the effect of feedlot RFI classification on enteric methane (CH4) production in the feedlot and on pasture. Seventy-three animals (25 with a low RFI, 24 with a medium RFI and 24 with a high RFI) classified in a feedlot performance test were subjected to performance testing on Brachiaria brizantha cv. Marandu pasture. Enteric CH4 was measured in a sample of these animals (n = 47, with high and low RFI) by the sulfur hexafluoride tracer-gas technique after the feedlot-performance test and during the performance test on pasture. In the feedlot-performance test, dry-matter intake (DMI) of low-RFI animals was 9.4% and 19.7% lower (P &lt; 0.05) than that of medium- and high-RFI animals respectively. However, there was no difference in DMI and, consequently, in RFI on pasture among animals classified as low, medium and high RFI. Accordingly, there is evidence of re-ranking of animals for RFI performance tested in the feedlot after weaning and, subsequently, on pasture. During the period of enteric CH4 measurement in the feedlot and on pasture, the DMI, neutral detergent-fibre intake and gross-energy intake of low-RFI animals were lower than those of high-RFI animals, and low-RFI animals exhibited greater DM and neutral detergent fibre digestibility only in the feedlot. Enteric CH4 production did not differ between low- and high-RFI animals either in the feedlot (101 and 107 g CH4/day) or on pasture (101 and 95.9 g CH4/day). A significant difference in CH4 yield (CH4/kg DMI) was observed on pasture between animals with low and high RFI (17.6 and 13.7 g CH4/kg DMI respectively). The results did not support the hypothesis that an increase in feed efficiency, evaluated in growing animals in feedlot-performance tests, decreases enteric CH4 production (g/day) proportionally to the lower DMI.

The effects of feeding 3-nitrooxypropanol at two doses on milk production, rumen fermentation, plasma metabolites, nutrient digestibility, and methane emissions in lactating Holstein cows

The objective of this study was to determine the effects of feeding 3-nitrooxypropanol (NOP) in the total mixed ration of lactating Holstein cows on rumen fermentation, ruminal microbial population, enteric methane production, milk production, nutrient digestibility, and blood metabolites. Fifteen ruminally cannulated Holstein cows in mid to late lactation were used in a 3 × 3 Latin square design study with 28-day periods. Cows were fed a 60%-forage diet (dry matter basis) with 2500 (HIGH), 1250 (LOW) or 0 (CON) mg/day of NOP. After a 20-day diet adaptation period, dry matter intake (DMI) and milk yield were recorded daily. Rumen digesta and rumen fluid were collected on Days 21 and 28 and ruminal pH was determined on Days 23–28. Methane emissions were measured on Days 23–27 using the sulfur hexafluoride tracer gas technique. Faecal and blood samples were taken on Days 25–27. Feeding NOP at either dose did not affect DMI, milk production or bodyweight gain. Total concentration of volatile fatty acids in rumen fluid did not differ; however, there was a decrease in molar proportion of acetate and increase in molar proportion of propionate with feeding NOP in a dose-dependent manner. Microbial profile and ruminal pH were not affected by treatment. Apparent total-tract digestibility of DM (62.7% vs 58.4%; P &lt; 0.05) and neutral detergent fibre (38.0% vs 30.7%; P &lt; 0.05) were increased with the HIGH dose compared with CON. Feeding NOP reduced methane yield from 19.9 to 15.3 g/kg DMI for CON versus LOW (P &lt; 0.05) and from 19.9 to 12.6 for CON versus HIGH (P &lt; 0.05). Feeding NOP at 1250 or 2500 mg/day reduced methane yield and affected ruminal volatile fatty acid profile without compromising DMI or apparent total-tract nutrient digestibility.

Supplementation with crushed rapeseed causes reduction of methane emissions from lactating dairy cows on pasture

The main objective of this study was to investigate the effect of supplementing a pasture diet with crushed rapeseed on enteric methane (CH4) emissions from lactating dairy cows. The experiment was conducted as a crossover design using eight multiparous lactating Norwegian red dairy cows [(means ± s.d.) 548 ± 52 kg bodyweight, 38 ± 14 days in milk and 35 ± 3.7 kg milk/day, at the start of the experiment] maintained in two groups and fed two diets in two periods with the second period extended (18 days) to investigate the persistence of the CH4 response. Four of the eight cows were fitted with a rumen cannula with two cannulated cows assigned to each group. Cows were maintained on pasture (24 h/day) with access to 9 kg/day of concentrate containing 10% crushed rapeseed (RSC) or a control concentrate (CC). Dietary fat content was 63 g/kg dry matter for RSC and 42 g/kg dry matter for CC. The CH4 production was measured for five consecutive days in each period using the sulfur hexafluoride tracer gas technique. Compared with CC, RSC caused a reduction in enteric CH4 emission (221 vs 251 g/day and 8.1 vs 9.0 g/kg of energy-corrected milk), and this response persisted in the extension period. Cows fed RSC had higher milk yield compared with cows fed CC (31.7 vs 29.6 kg/day). However, milk fat and protein content were lower in milk from cows fed RSC than CC. Therefore, energy-corrected milk was not affected by treatment. Feeding RSC lowered milk fat content of palmitic acid compared with CC. The study showed that adding crushed RSC to the diet can be an effective means of reducing CH4 emissions from lactating dairy cows on pasture, without negatively affecting milk production.

The effects of feeding 3-nitrooxypropanol on methane emissions and productivity of Holstein cows in mid lactation

The objective of the current study was to determine the effects of adding 3-nitrooxypropanol to the diet of lactating Holstein cows on methane emissions, rumen fermentation, ruminal microbial profile, and milk production. Twelve ruminally cannulated Holstein cows in midlactation were used in a crossover design study with 28-d periods. Cows were fed a diet containing 38% forage on a dry matter basis with either 2,500mg/d of 3-nitrooxypropanol (fed as 25g of 10% 3-nitrooxypropanol on silicon dioxide) or 25g/d of silicon dioxide (control). After a 21-d diet adaptation period, dry matter intake (DMI) and milk yield were recorded daily. Rumen fluid and digesta were collected on d 22 and 28 for volatile fatty acid analysis and microbial profiling. Enteric methane emissions were measured on d 23 to 27 using the sulfur hexafluoride tracer gas technique. Feeding 3-nitrooxypropanol did not affect DMI; however, methane production was reduced from 17.8 to 7.18g/kg of DMI. No change in milk or milk component yields was observed, but cows fed 3-nitrooxypropanol gained more body weight than control cows (1.06 vs. 0.39kg/d). Concentrations of total volatile fatty acids in ruminal fluid were not affected by treatment, but a reduction in acetate proportion and a tendency for an increase in propionate proportion was noted. As such, a reduction in the acetate-to-propionate ratio was observed (2.02 vs. 2.36). Protozoa counts were not affected by treatment; however, a reduction in methanogen copy count number was observed when 3-nitrooxypropanol was fed (0.95 vs. 2.69 × 108/g of rumen digesta). The data showed that feeding 3-nitrooxypropanol to lactating dairy cows at 2,500mg/d can reduce methane emissions without compromising DMI or milk production.

Methane emissions, body composition, and rumen fermentation traits of beef heifers differing in residual feed intake1

This study examined the relationship of residual feed intake (RFI) and performance with methane emissions, rumen fermentation, and digestion in beef heifers. Individual DMI and growth performance were measured for 22 Simmental heifers (mean initial BW 449 kg, SD = 46.2 kg) offered grass silage ad libitum for 120 d. Ultrasonically scanned muscle and fat depth, BCS, muscularity score, skeletal measurements, blood variables, rumen fermentation (via stomach tube), and total tract digestibility (indigestible marker) were measured. Methane production was estimated using the sulfur hexafluoride tracer gas technique over two 5-d periods beginning on d 20 and 75 of the RFI measurement period. Phenotypic RFI was calculated as actual DMI minus expected DMI. The residuals of the regression of DMI on ADG and midtest metabolic body weight, using all heifers, were used to compute individual RFI coefficients. Heifers were ranked by RFI and assigned to low (efficient), medium, or high (inefficient) groupings. Overall ADG and DMI were 0.58 kg (SD = 0.18) and 7.40 kg (SD = 0.72), respectively. High-RFI heifers consumed 9 and 15% more (P < 0.05) than medium- and low-RFI groups, respectively. Body weight, growth, skeletal, and composition traits did not differ (P > 0.05) between low- and high-RFI groups. High-RFI heifers had higher concentrations of plasma glucose (6%) and urea (13%) and lower concentrations of plasma creatinine (9%) than low-RFI heifers (P < 0.05). Rumen pH and apparent in vivo digestibility did not differ (P > 0.05) between RFI groups, although acetate:propionate ratio was lowest (P = 0.07) for low-RFI (3.5) and highest for high-RFI (4.6) heifers. Methane production expressed as grams per day or grams per kilogram metabolic body weight was greater (P < 0.05) for high (297 g/d and 2.9 g/kg BW0.75) compared with low (260 g/d and 2.5 g/kg BW0.75) RFI heifers, with medium (275 g/d and 2.7 g/kg BW0.75) RFI heifers being intermediate. Regression analysis indicated that a 1 kg DM/d increase in RFI was associated with a 23 g/d increase (P = 0.09) in methane emissions. Results suggest that improved RFI will reduce methane emissions without affecting productivity of growing beef cattle.

Technical Note: Can the sulfur hexafluoride tracer gas technique be used to accurately measure enteric methane production from ruminally cannulated cattle?

An experiment was conducted to determine whether using ruminally cannulated cattle affects the estimate of enteric methane (CH(4)) emissions when using the sulfur hexafluoride (SF(6)) tracer technique with samples taken from a head canister. Eleven beef cattle were surgically fitted with several types of ruminal cannula (2C, 3C, 3C+washer, 9C; Bar Diamond, Parma, ID). The 2C and 3C models (outer and inner flanges with opposite curvature) had medium to high leakage, whereas the 9C models (outer and inner flanges with the same curvature) provided minimum to moderate leakage of gas. A total of 48 cow-day measurements were conducted. For each animal, a permeation tube containing sulfur hexafluoride (SF(6)) was placed in the rumen, and a sample of air from around the nose and mouth was drawn through tubing into an evacuated canister (head canister). A second sample of air was collected from outside the rumen near the cannula into another canister (cannula canister). Background concentrations were also monitored. The methane (CH(4)) emission was estimated from the daily CH(4) and SF(6) concentrations in the head canister (uncorrected). The permeation SF(6) release rate was then partitioned based on the proportion of the SF(6) concentration measured in the head vs. the cannula canister. The CH(4) emissions at each site were calculated using the two release rates and the two CH(4):SF(6) concentration ratios. The head and cannula emissions were summed to obtain the total emission (corrected). The difference (corrected - uncorrected) in CH4 emission was attributed to the differences in CH(4):SF(6) ratio at the 2 exit locations. The proportions of CH(4) and SF(6) recovered at the head were greater (P < 0.001) for the 9C cannulas (64% and 66%) compared with the other cannulas, which were similar (P > 0.05; 2C, 6% and 4%; 3C, 17% and 15%; 3C+washer, 19% and 14%). Uncorrected CH(4) emissions were ± 10% of corrected emissions for 53% of the cow-day measurements. Only when more than 80% of the SF(6) escaped via the rumen did the difference between the uncorrected and corrected CH(4) emissions exceed 20%. We concluded that using cannulated cattle introduces more variability into the SF(6) technique used with a head canister, a technique that is already highly variable. Thus, use of cannulated animals is not recommended when using the SF(6) technique with head canister. However, if cannulated cattle are used, the cannulas need to be tight-fitting to minimize leakage, and large animal numbers are needed to overcome the additional variability.

A fibrolytic enzyme additive for lactating Holstein cow diets: Ruminal fermentation, rumen microbial populations, and enteric methane emissions

The objective was to determine if supplementing a dairy cow diet with an exogenous fibrolytic enzyme additive (Econase RDE; AB Vista, Marlborough, Wiltshire, UK) altered fermentation, pH, and microbial populations in the rumen or enteric methane (CH4) emissions. In a companion study, this enzyme additive improved efficiency of fat-corrected milk production in a dose-dependent manner by up to 11% for early lactation dairy cows. Nine ruminally cannulated, lactating Holstein cows were used in a replicated 3×3 Latin square design with 21-d periods. Dietary treatments were 0 (control), 0.5 (low), and 1.0 (high) mL of enzyme/kg of total mixed ration dry matter. Rumen contents were collected on 2 d (d 15 and 19), ruminal pH was measured continuously for 6 d (d 13 to 18) by using an indwelling system, and enteric CH4 production was measured for 3 d (d 16 to 18) using the sulfur hexafluoride tracer gas technique. The enzyme additive did not alter volatile fatty acids, NH3, pH, or population densities of total protozoa, bacteria, and methanogens in ruminal fluid. However, population densities of certain bacteria, calculated as copy number of species-specific 16S-rRNA, were affected by enzyme treatment. Population density of Ruminobacter amylophilus was increased and that of Fibrobacter succinogenes tended to be increased by the high enzyme treatment. Selenomonas ruminantium tended to increase linearly with increasing levels of enzyme in the diet, although its population density was only numerically increased by the high enzyme treatment. Streptococcus bovis, however, tended to be decreased by the low enzyme treatment. Increasing the level of enzyme supplement in the diet also linearly increased enteric CH4 production, even when adjusted for feed intake or milk production (19.3, 20.8, and 21.7g of CH4/kg of dry matter intake or 12.9, 13.6, and 15.1g of CH4/kg of milk for the control, low, and high enzyme treatments, respectively). This shift in ruminal bacterial communities and higher CH4 emissions could imply increased ruminal digestion of feed, which needs to be substantiated in longer term studies.

Linseed suppresses enteric methane emissions from cattle fed barley silage, but not from those fed grass hay

This study investigated potential effects of feeding ground linseed on enteric CH4 production, ruminal fermentation and nutrient digestibility in cattle when it was added to diets containing grass hay or barley silage. Twelve non-lactating ruminally cannulated Holstein cows were used in a replicated 4×4 Latin Square design experiment with four diets and four 21d periods. Experimental diets (500:500 forage to concentrate ratio; dry matter (DM) basis) were used in a 2×2 factorial design using either chopped grass hay or whole crop barley silage as the forage source with or without ground linseed at 150g/kg ration DM as a partial replacement for barley grain. Diets were fed once daily as total mixed rations. Rumen contents were collected on days 14 and 21 of each period. In situ ruminal digestibility of grass hay and barley silage was measured at 24 and 48h of incubation on days 15 and 16. Apparent total tract digestibility of dietary nutrients was estimated by collecting fecal samples from the rectum of each cow twice daily from days 15 to 21. Indigestible aNDF was used as an internal marker to estimate apparent diet digestibility in the total tract. Enteric CH4 production was measured from days 17 to 19 using the sulfur hexafluoride tracer gas technique. Without linseed inclusion, cows fed the diet based on grass hay produced 31% less CH4 as g/hd/d and up to 30% less CH4/kg of DM, digested DM or digested organic matter intake, or as MJ CH4/MJ gross energy intake (forage×linseed interaction, P<0.01) versus cows fed the diet based on barley silage. Including linseed in the hay based diet did not suppress CH4 emissions, whereas including linseed in the silage based diet reduced enteric CH4 emissions by 36% as gCH4/hd/d, by 33% as gCH4/kgDM intake, by 28% as gCH4/kg digested DM and by 37% as MJCH4/MJ gross energy intake (forage×linseed interaction, P<0.01). Linseed inclusion lowered CH4 emissions of cows fed the silage based diet by depressing ruminal fermentation (i.e., reduced protozoal population, decreased total volatile fatty acid concentration (forage×linseed interaction: P<0.01), ruminal digestion (i.e., lower 48h in situ silage fibre disappearance; linseed effect: P≤0.05) and total tract diet digestibility (linseed effect: P≤0.03). Depressive effects of linseed on these variables were less pronounced for the hay based diet. Results show that including ground linseed in a barley silage based diet can mitigate enteric CH4 emissions, but not in a grass hay based diet.This paper is part of the special issue entitled: Greenhouse Gases in Animal Agriculture – Finding a Balance between Food and Emissions, Guest Edited by T.A. McAllister, Section Guest Editors: K.A. Beauchemin, X. Hao, S. McGinn and Editor for Animal Feed Science and Technology, P.H. Robinson.

Differing effects of 2 active dried yeast (Saccharomyces cerevisiae) strains on ruminal acidosis and methane production in nonlactating dairy cows

Fifteen ruminally cannulated, nonlactating Holstein cows were used to measure the effects of 2 strains of Saccharomyces cerevisiae, fed as active dried yeasts, on ruminal pH and fermentation and enteric methane (CH4) emissions. Nonlactating cows were blocked by total duration (h) that their ruminal pH was below 5.8 during a 6-d pre-experimental period. Within each block, cows were randomly assigned to control (no yeast), yeast strain 1 (Levucell SC), or yeast strain 2 (a novel strain selected for enhanced in vitro fiber degradation), with both strains (Lallemand Animal Nutrition, Montréal, QC, Canada) providing 1×1010 cfu/head per day. Cows were fed once daily a total mixed ration consisting of a 50:50 forage to concentrate ratio (dry matter basis). The yeast strains were dosed via the rumen cannula daily at the time of feeding. During the 35-d experiment, ruminal pH was measured continuously for 7 d (d 22 to 28) by using an indwelling system, and CH4 gas was measured for 4 d (d 32 to 35) using the sulfur hexafluoride tracer gas technique (with halters and yokes). Rumen contents were sampled on 2 d (d 22 and 26) at 0, 3, and 6h after feeding. Dry matter intake, body weight, and apparent total-tract digestibility of nutrients were not affected by yeast feeding. Strain 2 decreased the average daily minimum (5.35 vs. 5.65 or 5.66), mean (5.98 vs. 6.24 or 6.34), and maximum ruminal pH (6.71 vs. 6.86 or 6.86), and prolonged the time that ruminal pH was below 5.8 (7.5 vs. 3.3 or 1.0 h/d) compared with the control or strain 1, respectively. The molar percentage of acetate was lower and that of propionate was greater in the ruminal fluid of cows receiving strain 2 compared with cows receiving no yeast or strain 1. Enteric CH4 production adjusted for intake of dry matter or gross energy, however, did not differ between either yeast strain compared with the control but it tended to be reduced by 10% when strain 2 was compared with strain 1. The study shows that different strains of S. cerevisiae fed as active dried yeasts vary in their ability to modify the rumen fermentative pattern in nonlactating dairy cows. Because strain 2 tended (when compared with strain 1) to lower CH4 emissions but increase the risk of acidosis, it may be prudent to further evaluate this strain in cattle fed high-forage diets, for which the risk of acidosis is low but CH4 emissions are high.

Methane emissions from yak ( Bos grunniens) steers grazing or kept indoors and fed diets with varying forage:concentrate ratio during the cold season on the Qinghai-Tibetan Plateau

For national greenhouse gas inventories, exact data on all major domesticated livestock systems are required. Such data is completely lacking for yak ( Bos grunniens) and, as this ruminant livestock species seems to have digestion and metabolism which differs from cattle, making data extrapolations from cattle are potentially inaccurate. In the present study methane (CH 4) emissions from yak were estimated under grazing and indoor feeding conditions in the cold season on the Qinghai-Tibetan Plateau at >3200 m above sea level. Twelve 3 year old growing yak steers (175 ± 10.7 kg) were subjected to measurements of CH 4 output using the sulfur hexafluoride tracer gas technique, nutrient intake and apparent digestibilities. The first group of three yaks grazed on native winter alpine meadows, while the indoor groups were fed either oat hay or total mixed diets of oat hay and concentrate in ratios of 0.6:0.4 and 0.4:0.6, respectively, on a dry matter (DM) basis. The experimental period lasted for 6 weeks, with the first 5 weeks for adaptation and the last for measurement. The oat hay contained slightly more crude protein (CP) and less fiber compared to the winter pasture grass, while inclusion of concentrate increased the CP intake of the yaks considerably. Yaks fed indoors gained body weight (BW) during the experimental period (about 200 g/day and slightly higher with concentrate), while grazing yaks lost 550 g/day of BW. Daily CH 4 emissions of the grazing yaks were 81.4 g/day or 1.68 g/kg BW 0.75 at an estimated daily grass DM intake of 3.78 kg. Absolute levels of CH 4 emissions were slightly higher in the oat hay fed yaks. Compared to the oat hay treatment, CH 4 production declined by 0.3 and 0.4 with forage:concentrate ratios of 0.6:0.4 and 0.4:0.6, respectively. Overall, the average proportion of gross energy lost as CH 4 energy (kJ/MJ) was 54 ± 15.2. These values are the ‘CH 4 emission factors’ (according to ‘Tier 1’ of IPCC, 2006) of about 28 kg/year for grazing non-lactating yaks weighing 175 kg. When adjusted to metabolic BW, yaks were at the lower range of CH 4 emission compared to cattle, while they were average when CH 4 was related to DM and gross energy intake. Implementing proper grazing management practices to improve winter diet quality and quantity, and thus animal productivity, can be expected to substantially mitigate CH 4 emissions per unit of meat and milk produced by yak.