Effect of nitrogen fertilization rate and regrowth interval of grass herbage on methane emission of zero-grazing lactating dairy cows

Abstract

Dairy cattle farming in temperate regions often relies on grass herbage (GH)-based diets but the effect of several grass management options on enteric CH4 emission has not been fully investigated yet. We investigated the combined effect of N fertilization rate and length of regrowth period of GH (predominantly ryegrass) on CH4 emission from lactating dairy cows. In a randomized block design, 28 lactating Holstein-Friesian dairy cows received a basal diet of GH and compound feed [85:15; dry matter (DM) basis]. Treatments consisted of GH cut after 3 or 5 weeks of regrowth, after receiving either a low (20kg of N/ha) or a high (90kg of N/ha) fertilization rate after initial cut. Feed intake, digestibility, milk production and composition, N and energy balance, and CH4 emission were measured during a 5-d period in climate respiration chambers after an adaptation to the diet for 12d. Cows were restricted-fed during measurements and mean DM intake was 15.0±0.16kg/d. Herbage crude protein content varied between 76 and 161g/kg of DM, and sugar content between 186 and 303g/kg of DM. Fat- and protein-corrected milk (FPCM) and feed digestibility increased with increased N fertilization rates and a shorter regrowth interval. Increasing the N fertilization rate increased daily CH4 emission per cow (+10%) and per unit of DM intake (+9%), tended to increase the fraction of gross energy intake emitted as CH4 (+7%), and (partly because of the low crude protein content for the low fertilized GH) only numerically reduced CH4 per unit of FPCM. The longer regrowth interval increased CH4 emission per unit of FPCM (+14%) compared with the shorter regrowth interval, but did not affect CH4 emission expressed in any other unit. With increasing N fertilization CH4 emission decreased per unit of digestible neutral detergent fiber intake (-13%) but not per unit of digestible organic matter intake. There was no interaction of the effect of N fertilization rate and regrowth interval on CH4 emission, but effects of N fertilization were generally most distinct with GH of 5 wk regrowth. The present results suggest that altering grass quality through an increase of N fertilization and a shorter regrowth interval can reduce CH4 emission in zero-grazing dairy cows, depending on the unit in which it is expressed. The larger amount of CH4 produced per day and cow with the more intensively managed GH is compensated by a higher feed digestibility and FPCM yield.

Effects of nitrogen fertilisation rate and maturity of grass silage on methane emission by lactating dairy cows

“…This may explain the relatively small amount of CH 4 per unit of FPCM with LF grass silage and, thus, explain the similar CH 4 emission levels between N fertilisation rates in the present study in contrast to the differences simulated by Bannink et al (2010). Grass silage quality effects described in the present study were generally in line with those observed for dairy cows offered grass herbage under zero-grazing conditions (Warner et al, 2015). Increasing the grass maturity from 3 to 5 weeks of regrowth increased CH 4 per unit of FPCM by 14%, whereas increasing the N fertilisation rate from 20 to 90 kg of N/ha did not affect CH 4 emissions.…”

“…Increasing the grass maturity from 3 to 5 weeks of regrowth increased CH 4 per unit of FPCM by 14%, whereas increasing the N fertilisation rate from 20 to 90 kg of N/ha did not affect CH 4 emissions. The grass silages tested in the present study generated 8% more daily CH 4 per cow than the grass herbage tested by Warner et al (2015). Nonetheless, emitted CH 4 per unit of FPCM was slightly lower (−4%) in the present study due to a considerably larger milk production (+16%) realised with grass silage at comparable DMI levels.…”

“…However, the present results are in line with a study of Boadi and Wittenberg (2002) in which medium-quality grass hay (50.7% in vitro OM digestibility) generated 10% more CH 4 per unit of DOMI than high-quality grass hay (61.5% in vitro OM digestibility) offered restrictedly to dairy and beef heifers, and in line with a study of Pinares-Patiño et al (2003) in which Charolais cows grazing timothy at heading stage (74.8% OM digestibility based on faecal N index method) produced 12% more CH 4 per unit of DOMI than when grazing timothy at early-vegetative stage (77.6% OM digestibility). In contrast, when dairy cows were offered grass herbage under zero-grazing conditions (Warner et al, 2015), CH 4 per unit of DOMI was not affected by either grass maturity or N fertilisation rate, whereas CH 4 declined by 9% per unit of DNDFI with high-compared with low-fertilised grass (90 v. 20 kg of N/ha, respectively). Despite a clear reduction in NDF digestibility by 12% units with advancing grass maturity in the present study, grass silage quality did not affect DNDFI levels and CH 4 per unit of DNDFI.…”

Digestion and nitrogen metabolism in beef cattle and in vitro rumen fermentation of autumn grass differing in fertilizer nitrogen application rate

“…Consequently, changes in grass total N concentration on this site may be relatively less responsive to divergent inorganic fertilizer N application rates (Keating & O'Kiely, ). Nevertheless, the magnitude of difference obtained for the grass CP concentration is comparable to that reported by Peyraud et al () (44 g/kg DM), Hennessy, O'Donovan, French, and Laidlaw () (39 g/kg DM: autumn) and Warner et al () (61 g/kg DM) for L. perenne ‐dominant swards that received inorganic fertilizer N application rates of 0 or 80 kg/ha (per cut), 5 or 50 kg/ha (per 4 week rotation) and 20 or 90 kg fertilizer N/ha respectively. In the current experiment, an increase in CP concentration of 10 g/kg DM was associated with a decrease in WSC concentration of 14.8 g/kg DM.…”

The Contribution of Mathematical Modeling to Understanding Dynamic Aspects of Rumen Metabolism

“…In vivo measurements confirm the merit of adopting a more dynamic approach as it demonstrates the limiting effect of N supply on rumen fiber digestion at similar crude protein contents in dietary DM. A crude protein level of 11.5% in maize silage diets was tested by Spek et al (2013) and a level of 10.3% in grass herbage diets was tested by Warner et al (2015), which in both studies resulted in a rumen ammonia concentration below 2 mM which is considered to be well below critical levels for ensuring optimal microbial activity (Dijkstra et al, 1998). The static model calculated a rumen protein balance of around zero at this low protein level (Spek et al, 2013), hence falling within recommendations.…”