Our study compared methane (CH4) emissions from lactating dairy cows measured using the sulfur hexafluoride (SF6) tracer and open-circuit respiration chamber techniques. The study was conducted using 16 lactating Holstein-Friesian cows. In each chamber, the cow was fitted with the SF6 tracer apparatus to measure total CH4 emissions, including emissions from the rectum. Fresh ryegrass pasture was harvested daily and fed ad libitum to each cow with a supplement of 5 kg of grain/d. The CH4 emissions measured using the SF6 tracer technique were similar to those using the chamber technique: 331 vs. 322 g of CH4/d per cow. The accuracy of the SF6 tracer technique was indicated by considering the ratio of the CH4 emission measured using the SF6 tracer to the emission measured using the chamber for each cow on each day. The calculated ratio of 102.3% (SE = 1.51) was not different from 100%. A higher variability within cow between days was found for the SF6 tracer technique [coefficient of variation (CV) = 6.1%] than for the chamber technique (CV = 4.3%). The variability among cows was substantially higher than within cows, and was higher for the SF6 technique (CV = 19.6%) than for the chamber technique (CV = 17.8%). Our CH4 emission data were compared with whole-animal chamber studies conducted in Canada and Ireland. In the Canadian study the SF6 technique did not measure CH4 emissions from the rectum and emissions were 8% lower than those measured using the chamber, indicating that emissions from the rectum may be greater than previously measured (1%). The relationship between CH4 emission and dry matter intake was examined for our data and for that reported in the Canadian study. There was a difference in the slopes of the regressions derived from our data and that from Canada; 17.1 vs. 20.8 g of CH4/kg of dry matter intake. A difference between the 2 locations was expected based on the difference in diet composition for these 2 studies. The SF6 tracer technique is reasonably accurate for inventory purposes and for evaluating the effects of mitigation strategies on CH4 emissions.

Abstract. The methods for estimating methane emissions from cattle as used in the Australian national inventory are based on older data that have now been superseded by a large amount of more recent data. Recent data suggested that the current inventory emissions estimates can be improved. To address this issue, a total of 1034 individual animal records of daily methane production (MP) was used to reassess the relationship between MP and each of dry matter intake (DMI) and gross energy intake (GEI). Data were restricted to trials conducted in the past 10 years using open-circuit respiration chambers, with cattle fed forage-based diets (forage >70%). Results from diets considered to inhibit methanogenesis were omitted from the dataset. Records were obtained from dairy cattle fed temperate forages (220 records), beef cattle fed temperate forages (680 records) and beef cattle fed tropical forages (133 records). Relationships were very similar for all three production categories and single relationships for MP on a DMI or GEI basis were proposed for national inventory purposes. These relationships were MP (g/day) = 20.7 (AE0.28) · DMI (kg/day) (R 2 = 0.92, P < 0.001) and MP (MJ/day) = 0.063 (AE0.008) · GEI (MJ/day) (R 2 = 0.93, P < 0.001). If the revised MP (g/day) approach is used to calculate Australia's national inventory, it will reduce estimates of emissions of forage-fed cattle by 24%. Assuming a global warming potential of 25 for methane, this represents a 12.6 Mt CO 2 -e reduction in calculated annual emissions from Australian cattle.

This study examined effects on milk yield and composition, milk fatty acid concentrations and methane (CH4) emissions when dairy cows were offered diets containing different amounts of algal meal. The algal meal contained 20% docosahexaenoic acid (DHA) and cows were offered either 0, 125, 250, or 375 g/cow per d of algal meal corresponding to 0, 25, 50, or 75 g of DHA/cow per d. Thirty-two Holstein cows in mid lactation were allocated to 4 treatment groups, and cows in all groups were individually offered 5.9k g of dry matter (DM) per day of concentrates [683 g/kg of cracked wheat (Triticum aestivum), 250 g/kg of cold-pressed canola, 46 g/kg of granulated dried molasses, and 21 g/kg of mineral mix] and ad libitum alfalfa (Medicago sativa) hay. The algal meal supplement was added to the concentrate allowance and was fed during the morning and afternoon milking, whereas the alfalfa hay was fed individually in pens. Cows were gradually introduced to their diets over 7d and then fed their treatment diets for a further 16d. Dry matter intake and milk yield were measured daily, and milk composition was measured on a sample representative of the daily milk yield on Thursday of each week. For the last 2d of the experiment, cows were individually housed in respiration chambers to allow measurement of CH4 emissions. Dry matter intake, milk yield and milk composition were also measured while cows were in the respiration chambers. Cows ate all their offered concentrates, but measured intake of alfalfa decreased with increasing dose of DHA by 16.2, 16.4, 15.1, and 14.3 kg of DM/d, respectively. Milk yield (22.6, 23.5, 22.6, and 22.6 kg/cow per d) was not affected by DHA dose, but milk fat concentrations (49.7, 37.8, 37.0, and 38.3g/kg) and, consequently, milk fat yields (1.08, 0.90, 0.83, and 0.85 kg/d) decreased with addition of DHA. The feeding of algal meal high in DHA was associated with substantial increases in the concentrations of DHA (0.04, 0.36, 0.60, and 0.91 g/100g of milk fatty acids) and conjugated linoleic acid C18:2 cis-9,trans-11 (0.36, 1.09, 1.79, and 1.87 g/100g of milk fatty acids). Addition of DHA did not affect total emissions of CH4 (543, 563, 553, and 520 g/cow per d), nor emissions in terms of milk production (24.9, 22.1, 24.3, and 23.4 g of CH4/kg of milk), but emissions were increased with respect to total intake (22.6, 23.5, 24.5, and 24.4 g of CH4/kg of DM). These findings indicate that CH4 emissions were not reduced when dairy cows were fed a forage-based diet supplemented with DHA from algal meal.

Grape marc (the skins, seeds, stalk, and stems remaining after grapes have been pressed to make wine) is currently a by-product used as a feed supplement by the dairy and beef industries. Grape marc contains condensed tannins and has high concentrations of crude fat; both these substances can reduce enteric methane (CH4) production when fed to ruminants. This experiment examined the effects of dietary supplementation with either dried, pelleted grape marc or ensiled grape marc on yield and composition of milk, enteric CH4 emissions, and ruminal microbiota in dairy cows. Thirty-two Holstein dairy cows in late lactation were offered 1 of 3 diets: a control (CON) diet; a diet containing dried, pelleted grape marc (DGM); and a diet containing ensiled grape marc (EGM). The diet offered to cows in the CON group contained 14.0kg of alfalfa hay dry matter (DM)/d and 4.3kg of concentrate mix DM/d. Diets offered to cows in the DGM and EGM groups contained 9.0kg of alfalfa hay DM/d, 4.3kg of concentrate mix DM/d, and 5.0kg of dried or ensiled grape marc DM/d, respectively. These diets were offered individually to cows for 18d. Individual cow feed intake and milk yield were measured daily and milk composition measured on 4d/wk. Individual cow CH4 emissions were measured by the SF6 tracer technique on 2d at the end of the experiment. Ruminal bacterial, archaeal, fungal, and protozoan communities were quantified on the last day of the experiment. Cows offered the CON, DGM, and EGM diets, ate 95, 98, and 96%, respectively, of the DM offered. The mean milk yield of cows fed the EGM diet was 12.8kg/cow per day and was less than that of cows fed either the CON diet (14.6kg/cow per day) or the DGM diet (15.4kg/cow per day). Feeding DGM and EGM diets was associated with decreased milk fat yields, lower concentrations of saturated fatty acids, and enhanced concentrations of mono- and polyunsaturated fatty acids, in particular cis-9,trans-11 linoleic acid. The mean CH4 emissions were 470, 375, and 389g of CH4/cow per day for cows fed the CON, DGM, and EGM diets, respectively. Methane yields were 26.1, 20.2, and 21.5g of CH4/kg of DMI for cows fed the CON, DGM, and EGM diets, respectively. The ruminal bacterial and archaeal communities were altered by dietary supplementation with grape marc, but ruminal fungal and protozoan communities were not. Decreases of approximately 20% in CH4 emissions and CH4 yield indicate that feeding DGM and EGM could play a role in CH4 abatement.

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