livestock cause climate change?

Farm animals account for a large amount of greenhouse gases emitted into the atmosphere from agriculture.  On average a cow releases between 70 and 120kg of methane per year!  Greenhouse gases are released from various areas of livestock breeding.  Carbon dioxide is released from the burning of fossil fuels for energy, such as electricity.  Monteny et al (2006) state an important source of methane is related to the way cows and other similar animals digest their food, whereas in chickens, pigs and other animals that digest their food differently, manure is the most important source of methane. The main sources of Nitrous oxide are in fertilisers, land applied animal manures and in the urine of grazing animals.  

Many mitigation strategies aim to reduce methane emissions from livestock as this is where the greatest proportions of emissions lie.  This is probably also because methane is one of the easier issues to mitigate as it is thought to be related to breed and diet of the animal.  This post will discuss the various ways in which methane can be mitigated through diet.  

Beauchemin et al (2007) undertook a study on cows, aiming to reduce methane emissions by altering their diet through adding lipids.  They found that cattle fed sunflower seeds produced less methane per day than cattle fed other lipid sources as the feed was less digestible.  Lipids reduce methane emissions by decreasing the amount of organic matter fermented in the rumen (part of the cow’s digestive system), as the lipids replaced barley grain.  Overall all lipid sources were equally effective in suppressing methane emissions (about 15%) when differences in intake and fibre digestion were accounted for.  However, adding lipids may increase the cost of feeding livestock, and therefore be less appealing to commercial farmers.  Beauchemin et al suggest sunflower oil as the best out of the three they used, as it increased rate of gain of the cattle as well as lowering methane emissions, hence being more attractive to farmers.  

Machmuller et al (2000) undertook a similar study to Beauchemin et al, but using sheep.  Sheep digest in a similar way to cows, so here they measured the change release of methane after adding different ingredients to their diets, against a control.  They found reductions in methane emissions from all, coconut oil 26%, rapeseed 19%, sunflower seed 27% and linseed 10%.  Again they found sunflower seed to reduce digestibility.  A possible problem with adding lipids and other supplements to animals diets is the reaction of buyers, people may be put off buying meat from animals that had these additives in their diet.  

Another possible way to alter livestock diet to reduce methane output is to change forage to concentrate ratios.  This is shown by a study by Lovett et al (2003), who investigated animal performance and methane emissions using 36 cows over an 11 week period.  They had various forage to concentrate ratios, some supplemented with coconut oils.  Reducing the forage to concentrate ratios resulted in significantly increased rates of weight gain, whereas the coconut oil had no impact on  weight gain of the cow.  Both the change to lower forage to concentrate ratios and the addition of coconut oil reduced daily methane emissions.  

These papers present reasonable strategies to mitigate methane emissions, an article by O’Mara et al (2008) in Livestock and Global Climate Change also suggests that both the addition of lipids and changing forage/concentrate ratio of livestock diets can reduce daily methane emissions.  However they say that more data and information need to be collected on diet alteration strategies .  It is necessary to ensure that these strategies are functional in different environments, can be easily adopted, and only have a small economic cost otherwise they will not appear appealing to farmers.