Abstract
The aim of this study was evaluate the relationship between the intensity of milk production for a wide range of Portuguese commercial cattle farms and NH3 and greenhouse gas (GHG) emissions from manure management and enteric fermentation. A survey was carried out at 1471 commercial dairy cattle farms (Holstein-Friesian) and the NH3, N2O and CH4 emissions at each stage of manure management were estimated as well as CH4 losses from enteric fermentation. Gaseous emissions were estimated by a mass flow approach and following the recommendations of IPCC guidelines. The manure management and enteric fermentation in a typical Portuguese cattle farm contributes with 7.5±0.15 g N/L milk produced as NH3 and 1.2±0.22 kg CO2 equivalent per litre of milk as GHG. Increasing milk production will significantly reduce NH3 and GHG emissions per litre of milk produced. It can be concluded that a win-win strategy for reducing NH3 and GHG emissions from dairy cattle farms will be the increase of milk production on these farms. This goal can be achieved by implementing animal breeding programs and improving feed efficiency in order to increase productivity.
Highlights
The aim of this study was evaluate the relationship between the intensity of milk production for a wide range of Portuguese commercial cattle farms and NH3 and greenhouse gas (GHG) emissions from manure management and enteric fermentation
The manure management and enteric fermentation in a typical Portuguese cattle farm contributes with 7.5±0.15 g N/L milk produced as NH3 and 1.2±0.22 kg CO2 equivalent per litre of milk as GHG
It can be concluded that a win-win strategy for reducing NH3 and GHG emissions from dairy cattle farms will be the increase of milk production on these farms
Summary
Previous studies (Casey & Holden, 2005; Fangueiro et al, 2008; Gerber et al, 2011) reported that, for a proper comparison between different farm intensities or milking systems, the environmental impacts generated should be expressed in function of production output (e.g., milk produced) together with per animal head or per hectare. Data for the whole year were collected and included the following parameters: cattle numbers and types (dairy cows, bulls, heifers and calves), milk production (liquid milk) and diets supplied (dry matter intake of concentrates, forages and crude protein). NH3 and N2O emissions were estimated following a mass-flow approach as described by Webb & Misselbrook (2004) and Dämmgen & Webb (2006), considering the N gaseous losses at each stage of manure management (e.g., housing, storage, land spreading and crop growing period). Considering Portuguese legislation (NREAP, 2013) regarding animal manure management, it was assumed a 30% reduction in NH3 emissions at land spreading, since the untreated cattle slurry was subjected to broadcast application and incorporation by plough within 12 h (EMEP-EEA, 2013). The CH4 emissions from manure management of all cattle, as well as emissions from enteric fermentation of the non dairy cows, were estimated by Tier 1 ap-
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