Does increasing milk yield per cow reduce greenhouse gas emissions? A system approach

Abstract

Milk yield per cow has continuously increased in many countries over the last few decades. In addition to potential economic advantages, this is often considered an important strategy to decrease greenhouse gas (GHG) emissions per kg of milk produced. However, it should be considered that milk and beef production systems are closely interlinked, as fattening of surplus calves from dairy farming and culled dairy cows play an important role in beef production in many countries. The main objective of this study was to quantify the effect of increasing milk yield per cow on GHG emissions and on other side effects. Two scenarios were modelled: constant milk production at the farm level and decreasing beef production (as co-product; Scenario 1); and both milk and beef production kept constant by compensating the decline in beef production with beef from suckler cow production (Scenario 2). Model calculations considered two types of production unit (PU): dairy cow PU and suckler cow PU. A dairy cow PU comprises not only milk output from the dairy cow, but also beef output from culled cows and the fattening system for surplus calves. The modelled dairy cow PU differed in milk yield per cow per year (6000, 8000 and 10 000 kg) and breed. Scenario 1 resulted in lower GHG emissions with increasing milk yield per cow. However, when milk and beef outputs were kept constant (Scenario 2), GHG emissions remained approximately constant with increasing milk yield from 6000 to 8000 kg/cow per year, whereas further increases in milk yield (10 000 kg milk/cow per year) resulted in slightly higher (8%) total GHG emissions. Within Scenario 2, two different allocation methods to handle co-products (surplus calves and beef from culled cows) from dairy cow production were evaluated. Results showed that using the 'economic allocation method', GHG emissions per kg milk decreased with increasing milk yield per cow per year, from 1.06 kg CO 2 equivalents (CO 2eq ) to 0.89 kg CO 2eq for the 6000 and 10 000 kg yielding dairy cow, respectively. However, emissions per kg of beef increased from 10.75 kg CO 2eq to 16.24 kg CO 2eq due to the inclusion of suckler cows. This study shows that the environmental impact (GHG emissions) of increasing milk yield per cow in dairy farming differs, depending upon the considered system boundaries, handling and value of co-products and the assumed ratio of milk to beef demand to be satisfied.

Herd monitoring to optimise fertility in the dairy cow: making the most of herd records, metabolic profiling and ultrasonography (research into practice)

“…A more global consideration is the environmental impact of beef production from the dairy v. the beef herd. As the animal maintenance cost of the dam is shared between milk and calf production, the perceived environmental impact of beef from the dairy herd is lower than that from dedicated beef herds (Zehetmeier et al, 2012). If cows had persistent lactations and did not require re-calving to stimulate milk production, periodic calving to produce beef calves with a short dry period may be environmentally and economically sustainable.…”

“…If cows had persistent lactations and did not require re-calving to stimulate milk production, periodic calving to produce beef calves with a short dry period may be environmentally and economically sustainable. However, the interactions between these systems are complex (Zehetmeier et al, 2012).…”

Whole-farm models to quantify greenhouse gas emissions and their potential use for linking climate change mitigation and adaptation in temperate grassland ruminant-based farming systems

“…For both grazing and confinement systems, the modelling methodology or the assumptions taken may in fact be a large source of uncertainty in the estimation of GHG emission O'Brien et al, 2011;Zehetmeier et al, 2012;Del Prado et al, 2013). For example, in studies of Zehetmeier et al (2012) and Del large differences were found after replacing the default equation Data collected from three different studies (Supplementary Table S3).…”

“…For example, in studies of Zehetmeier et al (2012) and Del large differences were found after replacing the default equation Data collected from three different studies (Supplementary Table S3). …”

Short communication: Impact of the intensity of milk production on ammonia and greenhouse gas emissions in Portuguese cattle farms

“…Nevertheless, Casey & Holden (2005) calculated GHG emissions ranged from 0.9 to 1.5 kg CO 2 equivalent per litre of milk in typical Irish dairy cattle farms and found a negative relationship between GHG emissions and the intensity of milk production, being comparable with the present study. In addition, increasing milk yield/cow will reduce GHG emissions, if these emissions are expressed per kg milk and reduction in associated beef production is not considered (Zehetmeier et al, 2012).…”