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The effect of concentrate feeding level on enteric CH 4 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 CH 4 emissions, production performance, and rumen fermentation of dairy cows grazing summer pasture (17 cows plus 3 cannulated cows per treatment). Enteric CH 4 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 CH 4 measurement period using TiO 2 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 CH 4 production (323 to 378 g/d) increased linearly due to the increase in total DMI, whereas CH 4 yield (29.1 to 25.1 g/kg of DMI) and CH 4 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 CH 4 mitigation option for dairy cows grazing kikuyu-dominant pasture in late summer when pasture is inherently fibrous.

Highlights• Dietary nitrate as methane mitigation strategy for grazing dairy cows • Concentrate DMI and milk yield decreased with nitrate addition • Total DMI was unaffected by treatment • Methane production and yield tended to decrease with nitrate addition • Ruminal pH fluid and total VFA concentration increased with nitrate addition AbstractDietary 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 x 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 to 3.7 kg/d) while pasture DMI increased linearly (9.1 to 11.4 kg/d) with increasing dietary nitrate addition. Methane production (313 to 280 g/d), CH4 yield (21.8 to 18.7 g/kg of DMI) and CH4 energy per gross energy intake (6.9 to 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 to 6.3) tended to increase while total volatile fatty acid (VFA) 3 concentration (99.9 to 104 mM/L) increased quadratically with increasing dietary nitrate addition. Individual VFA concentrations were unaffected by treatment. Rate of NDF disappearance (2.4 to 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 decreas...

Palm kernel expeller (PKE) is a feed by-product that is used by the dairy and beef industries. This study investigated the effect of partially replacing maize with PKE in a dairy concentrate on milk and ruminal fermentation parameters of Jersey cows grazing kikuyu-ryegrass pasture. Seventy-two multiparous cows were blocked according to milk yield, days in milk, and lactation number and randomly allocated within blocks to one of four treatment concentrates: PKE0, PKE10, PKE20, and PKE30, containing 0, 100, 200, and 300 g PKE/kg dry matter (DM), respectively. Eight rumen-cannulated lactating cows were used in a 4 x 4 Latin square design. All cows grazed pasture as one group, and concentrate was fed at 5.4 kg DM/cow per day. Pasture was allocated at 11.1 kg DM/cow per day. Milk yield was lower with PKE30 than PKE0 (14.3 versus 15.6 kg/cow per day, respectively). Feeding PKE20 and PKE30 was associated with a higher milk fat content of 50.6 and 52.9 g/kg, respectively, than that of 46.3 and 49.3 g/kg of cows fed PKE0 and PKE10, respectively. However, feeding PKE30 compromised fibre degradability. Increased milk fat content and sustained milk yield indicated that 200 g PKE/kg DM can partially replace maize in a dairy concentrate, resulting in a possible added economical advantage, which is dependent on the milk payment system. The lack of a significant effect on milk fat yield and the negative linear relationship of milk protein to milk fat ratio, induced by PKE inclusion, may be unfavourable for certain milk payment systems. ______________________________________________________________________________