Do you know how much your cows pollute?

Do you know how much your cows pollute?

Few years ago, I watched a documentary called “Cowspiracy” that was a big punch on my face. “Cowspiracy: The Sustainability Secret” is a 2014 documentary film which explores the impact of animal agriculture on the environment and investigates the policies of environmental organizations on this issue.

The film looks at various environmental concerns, including global warming, water use, deforestation, and ocean dead zones, and suggests that animal agriculture is the primary source of environmental destruction. Luckily, since then, things have changed and the animal science world has shown how cows, and ruminants in general, do not deserve that depiction, if well managed. Even the Union of Concerned Scientists has disputed the film’s assertion that most greenhouse gases driving climate change are produced by animal agriculture, as this runs counter to scientific consensus which is that the main cause is fossil fuel emissions. A 2018 peer-reviewed meta-analysis also found that a “no animal products” scenario would result in a 28% reduction in global greenhouse gas emissions across all sectors of the economy (Poore and Nemecek, 2018). So, it is true that the sector must face some challenges, but, as animal scientists, we must see the opportunities as well. Sometimes we forget in fact that a reduction of “leftovers” of animal production polluting our planet go in the same direction of having more efficient and productive animals, and therefore happy farmers!

Dairy production is one of those sectors that has received substantial scrutiny over the last years, leading to studies to evaluate and attempt to reduce nitrogen (N), phosphorus (P), and greenhouse gases (GHG) such as methane (CH4) and carbon dioxide (CO2). It is obvious that higher producing cows (because of better genetics and management) do leave more behind, but solutions are not simple. A global reduction of dairy cows’ pollutants has been in fact misinterpreted by claiming how the more intensive systems would result in larger amounts of pollutants.

Many studies have however shown how the higher producing cows leave less behind if we measure the amount of pollutant per unit of product (i.e. milk) and compare them with less intensive systems. We have therefore started to talk about productive efficiency, rather than just yield. Productive efficiency can be defined as “milk output per unit of resource input”, and the advantage from improved productive efficiency relates to what is referred to as the “dilution of maintenance” effect (Bauman et al., 1985; VandeHaar and St-Pierre, 2006). We also should never forget how dairy cows and other ruminants make use of many human food chain byproducts, that would otherwise go to waste, large amounts of feeds (i.e. forages) and non-protein N sources that do not compete with human food. There is also plenty of research on dietary practices that have been shown to reduce carbon-equivalent emissions. Those practices include addition of ionophores, fats, use of high quality forages, and increased use of grains. There are therefore some compromises and nutritional settings that need to be optimized and modern nutritional models can assist in this.

The Cornell Net Carbohydrates and Protein System, v.6.55 (CNCPS), is a model dealing with cattle and designed to be used in the field to predict, among the other things, nutrient excretion as part of a nutrient-management decision-making. NDS Professional (RUM&N, Reggio Emilia – Italy) is a licensed CNCPS platform and has implemented these predictions and added extra information (Figure 1). The CNCPS predictions for CH4 are based on the type of bovine (dry and lactating dairy cows or growing beef cattle) and, among the parameters used, include metabolizable energy available, intake of ADF, lignin and starch per day (Mills et al., 2003; Ellis et al., 2007). NDS Professional gives the possibility of comparing these values with other equations from the literature and expressed as grams of CH4 per kg of dry matter intake (DMI; Figure 2; Bell et al., 2016; INRA, 2016; Mills et al., 2003 and 2009; Moraes et al., 2014 and 2015; Nielsen et al., 2013; NorFor, 2013; Yan et al., 2000 and 2009). For CO2, the CNCPS predictions show a curvilinear relationship between CO2 emissions and DMI and milk yield (Russomanno et al., 2012) and they are reported in kg/day (Figure 3). NDS Professional, also in this case, has added other predictions for comparison purpose (Casper et al., 2010; Kirchgessner et al., 1991; NorFor, 2013; Ranga et al., 2014). Both CH4 and CO2 are then converted in various units to compare absolute and efficiency values across various scenarios (Figure 1).The full article is for subscribed members only. To view the full article please subscribe. It’s FREE!Log In Register


  • Department of Animal Sciences, Faculty of AgriSciences, Stellenbosch University RUM&N, Reggio Emilia - Italy


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