The objective of the present study was to compare the enteric methane (CH4) emissions and milk production of spring-calving Holstein-Friesian cows offered either a grazed perennial ryegrass diet or a total mixed ration (TMR) diet for 10 wk in early lactation. Forty-eight spring-calving Holstein-Friesian dairy cows were randomly assigned to 1 of 2 nutritional treatments for 10 wk: 1) grass or 2) TMR. The grass group received an allocation of 17 kg of dry matter (DM) of grass per cow per day with a pre-grazing herbage mass of 1,492 kg of DM/ha. The TMR offered per cow per day was composed of maize silage (7.5 kg of DM), concentrate blend (8.6 kg of DM), grass silage (3.5 kg of DM), molasses (0.7 kg of DM), and straw (0.5 kg of DM). Daily CH4 emissions were determined via the emissions from ruminants using a calibrated tracer technique for 5 consecutive days during wk 4 and 10 of the study. Simultaneously, herbage dry matter intake (DMI) for the grass group was estimated using the n-alkane technique, whereas DMI for the TMR group was recorded using the Griffith Elder feeding system. Cows offered TMR had higher milk yield (29.5 vs. 21.1 kg/d), solids-corrected milk yield (27.7 vs. 20.1 kg/d), fat and protein (FP) yield (2.09 vs. 1.54 kg/d), bodyweight change (0.54 kg of gain/d vs. 0.37 kg of loss/d), and body condition score change (0.36 unit gain vs. 0.33 unit loss) than did the grass group over the course of the 10-wk study. Methane emissions were higher for the TMR group than the grass group (397 vs. 251 g/cow per day). The TMR group also emitted more CH4 per kg of FP (200 vs. 174 g/kg of FP) than did the grass group. They also emitted more CH4 per kg of DMI (20.28 vs. 18.06 g/kg of DMI) than did the grass group. In this study, spring-calving cows, consuming a high quality perennial ryegrass diet in the spring, produced less enteric CH4 emissions per cow, per unit of intake, and per unit of FP than did cows offered a standard TMR diet.

Increasing milk production from pasture while increasing grass dry matter intake (GDMI) and lowering methane (CH(4)) emissions are key objectives of low-cost dairy production systems. It was hypothesized that offering swards of low herbage mass with increased digestibility leads to increased milk output. A grazing experiment was undertaken to investigate the effects of varying levels of HM on CH(4) emissions, GDMI and milk production of grazing dairy cows during the mid-season grazing period (June to July). Prior to the experiment, 46 Holstein-Friesian dairy cows (46 d in milk) were randomly assigned to 1 of 2 treatments (n=23) in a randomized block design. The 2 treatments consisted of 2 target pregrazing HM: 1,000 kg of dry matter (DM)/ha (low herbage mass, LHM) or 2,200 kg of DM/ha (high herbage mass, HHM). The experimental period lasted 2 mo from June 1 until July 31. Within the experimental period, there were 2 measurement periods, measurement 1 (M1) and measurement 2 (M2), where CH(4) emissions, GDMI, and milk production were measured. Mean herbage mass throughout the measurement periods was 1,075 kg of DM/ha and 1,993 kg of DM/ha for the LHM and HHM treatments, respectively. Grass quality in terms of organic matter digestibility was significantly higher for the LHM treatment in M2 (+12 g/kg of DM). In M1, the effect of herbage mass on grass quality was approaching significance in favor of the LHM treatment. Herbage mass did not significantly affect milk production during the measurement periods. Cows grazing the LHM swards had increased GDMI in M1 (+1.5 kg of DM) compared with cows grazing the HHM swards; no difference in GDMI was observed in M2. Grazing HHM swards increased CH(4) production per cow per day (+42 g), per kilogram of milk yield (+3.5 g/kg of milk), per kilogram of milk solids (+47 g/kg of milk solids), and per kilogram of GDMI (+3.1 g/kg of GDMI) in M2. Cows grazing the HHM swards lost a greater proportion of their gross energy intake as CH(4) during both measurement periods (+0.9% and +1% for M1 and M2, respectively). It was concluded that grazing LHM swards would increase grass quality with a concurrent reduction in CH(4) emissions.

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This study compared the enteric CH(4) emissions and milk production of cows offered various grass-based diets during mid to late lactation. Forty-eight spring-calving Holstein-Friesian dairy cows were randomly assigned to 1 of 3 nutritional treatments for 8 wk: (1) low grass allowance (LGA) + partial mixed ration (PMR), (2) high grass allowance (HGA), or (3) LGA. The PMR group received an allocation of 13.9 kg of grass dry matter (DM)/cow per day and in addition were offered 4.1 kg of PMR DM/cow per day. The HGA group received an allocation of 19.3 kg of grass DM/cow per day and the LGA group received an allocation of 14.4 kg of grass DM/cow per day. The PMR offered was composed of 450 g of maize silage/kg of DM, 450 g of concentrate blend/kg of DM, and 100g of barley straw/kg of DM. Daily CH(4) emissions were determined using the emissions from ruminants using a calibrated tracer technique, using sulfur hexafluoride, for 5 consecutive days during 2 periods. Simultaneously, grass DM intake (DMI) was estimated using the n-alkane technique and the PMR DMI was also recorded. Cows offered PMR had higher DMI than either the HGA or LGA cows (16.5 vs. 14.9 and 13.9 kg of DM/d). The higher DMI of PMR cows increased milk production relative to HGA and LGA cows: milk yield (17.0 vs. 14.6 and 13.1 kg) and fat and protein yield (1.29 vs. 1.14 and 1.04 kg). Daily CH(4) emissions were higher for the PMR group than for the HGA and LGA groups (406 vs. 384 and 349 g/cow per day). The enteric CH(4) emissions intensity per unit of DMI, milk yield, solids-corrected milk yield, and fat and protein yield did not differ between treatments. Effects observed in the PMR treatment were due to an increase in DMI rather than to any nutritional characteristic of the PMR.

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