Effect of pregrazing herbage mass on methane production, dry matter intake, and milk production of grazing dairy cows during the mid-season period

Abstract

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.

Effect of pre-grazing herbage mass on dairy cow performance, grass dry matter production and output from perennial ryegrass (Lolium perenne L.) pastures

“…Furthermore, the range in pre-grazing HM examined (846 kg DM/ha) in the current study was less than that investigated by previous authors. In agreement with the current study, Wims et al (2010) investigating a similar range in pre-grazing HM reported no effect on milk production, suggesting that the range in pre-grazing HM investigated was too narrow to influence daily milk production per cow. This suggestion is supported by McEvoy et al (2009) who investigated a range in pre-grazing HM from 1770 to 2360 kg DM/ha and failed to detect any effect of pre-grazing HM on milk production.…”

A modified sulphur hexafluoride tracer technique enables accurate determination of enteric methane emissions from ruminants

“…The rate of gas inflow through capillary tube declined by approximately 27% as canister pressure increased from 0.05 to 0.5 atm (Experiment 2). This effect was also observed when sampling-rate and canister-volume combinations reported in the literature were tested in Experiment 4 (e.g., Chaves et al, 2006;Wims et al, 2010). Between 0 and 24 h of collection, the rate of gas collection declined by 22% (Experiments 3 and 4) enabling acceptance of hypothesis 2.…”

“…The CAP100 apparatus was designed to represent that generally used by researchers who cite the method of Johnson et al (1994Johnson et al ( or 2007, e.g., Chaves et al (2006). The CAP1.5 apparatus was designed to represent the sample collection apparatus that incorporates a short crimped capillary-tube, e.g., Wims et al (2010). The OP5 sample collection apparatus formed the basis of the modified SF 6 technique that was tested in this study.…”

“…One widespread modification has been to use a short length of crimped capillary-tube as the flow restrictor (e.g., Hegarty et al, 2007;Wims et al, 2010;Williams et al, 2011). Typically a short section of 127 m ID capillarytube, between 10 and 20 mm in length, is crimped to reduce its air conductance to the desired rate and it is positioned within a gas tight Swagelok tube fitting.…”

Reducing the carbon footprint of Australian milk production by mitigation of enteric methane emissions

“…For example, many authors when describing short-term feeding experiments, have measured the total amount of enteric methane produced by a specific group of lactating cows in a particular period of an experiment, and then divided this amount by the total amount of milk produced by these same cows during the same period (e.g. Wims et al 2010;Moate et al 2011). We propose that this measure of methane (CH 4 ) intensity, which has units of g CH 4 /kg milk or milk solids (MS), should be defined as 'partial enteric methane intensity' (PEMI) because it does not take into account the enteric methane that is necessarily produced by growing heifers, non-lactating cows and bulls.…”