The reputation of domesticated ruminators as climate culprits has became spread in later years, due to their large emissions of the greenhouse gas methane (CH4). Especially cows in meat and dairy production are considered liable for a remarkable high share of the climate changing emissions, but other ruminators such as sheeps and goats are considered polluters, even if they don’t get as much attentions as the farting cows, as their total emission of carbon dioxide equivalents are lower due to smaller size and lesser numbers.
How bad are goats then? They’re small and cute, smells good (well, a doe does) and never farts loudly in public. Their ability to feed from forage inaccessible to other livestock, like bushes and leaves, makes them a great tool in keeping biodiversity and stimulate growth in young trees and herbs, leading to a greater uptake of carbon dioxide from the air. But do they actually pollute more more than they clean up?
There are actually a lot of studies published on the topic methane emission from goats, mostly from an economical view, since methane emission is considered a loss in energy uptake, that indicates a suboptimal ration.
When I started digging deeper in this issue, I realized that most goats in the studies where fed a completely different diet than our goats are. While our goats grazes freely during the six warm months eating a mix of grass, leaves, bark and needles, and during the winter eats mostly hay combined with spruce and pine needles, the goats in the studies where fed a single feed, chosen for optimizing milk production or feeding costs.
I got the notion that most goats in industrialized production are not getting their natural forage, and if they do, not in a natural mix. I know what usually happens to me when I do that to myself.
This study, Murciano-Granadina Goat Performance and Methane Emission after Replacing Barley Grain with Fibrous By-Products suggests that the ordinary forage of barley grain can be substituted with high fibrous orange peel or soy been hulls, without increasing methane emission. That is a good thing from a economical view, because those by-products probably is extraordinary cheap, but it says nothing about what a natural methane emission is, since all three rations are unnatural to a goat.
Another common mistake is to consider sheep and goats the same, as in this study: Energy metabolism and methane production in llamas, sheep and goats fed high- and low-quality grass-based diets. where goats, sheep and llamas are given a low fibrous and a high fibrous grass and the difference in methane emission is recorded. Only llamas showed lesser methane emission on the high fibrous diet. My conclusion: goats, nor sheep, do not do well on llama food.
What is the source of the methane then? The complex hydrocarbons in the food needs to be broken down into less complex molecules to be possible to absorb for the animal. In a ruminators digestion, this is an extremely complex process, with enzymes, yeast and bacteria working together decomposing those structures. Goats differs from sheep and cows, since they have an extremely fast digestion, giving them the possibility to decompose the most complex hydrocarbons, lignins, found in wood and all durable structures in the world of plants. The key to achieving this is mostly certain bacterial fermentation processes in the rumen. These bacteria seems to be increasing in numbers when the goat eats a lot of roughage, but decreases when the goat eats a lot of starch and sugars. Instead a methane producing bacteria increases when shorter hydrocarbons are digested.
This study: Methane emission by goats consuming diets with different levels of condensed tannins from lespedeza suggest a very interesting view, that in fact tannins are the key to reduce methane emissions. Even if the study is performed on forage consisting of only two species, the forage is more natural to the goat than in the other studies reviewed. The results is that when the goats are fed with a high tannin forage, the methane emission drops quadratically. The adaptation time of 4-6 days to the high tannin forage is another indicator of transformation in the bacterial balance.
In the study, two kinds of forage, sorghum grass and Kobe lespedeza (a legume, like clover or peas) are compared in different rations, 0/100, 33/67, 67/33 and 100/0. Where the 100% grass diet shows no drop in methane emission after 6 days, the 100% legume diet reduced the methane emission by 50% on day 5. After 20 days, the high tannin legume diet remained at low emission rates (from 10.3 to 10.9 l/day), while the 100% grass diet emission rate was drastically increased (from 20.4 to 26.2 l/day).
Tannins are found in many of the goats natural sources of roughage, such as leaves, bark, needles and branches. When the goat is allowed to forage freely in a diverse environment, the level of tannins would be significantly higher than when grassfed or grainfed.
Aren’t those tannins poisonous then? Yes, to cattle, sheep, and especially horses, a tannin fueled diet, such as lots of oak and beech leaves would be lethal. For a goat though, a much higher level of tannins seems to be acceptable. Several studies suggest that oak leaves are not only nutritious and reduces goat gasses, they also reduce nematode infections.
Amanda Karlsson in Effekten av toxiciteten hos ek för get, får och nötkreatur discusses the effects of oak leaves on goats, sheep and cattle, and concludes that oak toxication on goats are not likely, given they have the choice of eating the right amount.
J.Raju et. al. in Effect of feeding oak leaves (Quercus semecarpifolia vsQuercus leucotricophora) on nutrient utilization, growth performance and gastrointestinal nematodes of goats in temperate sub Himalayas suggests that forage with much higher tannin content than the Swedish oak are suitable for goats in the Himalayans, and protects against parasites.
Content of condensed tannins in the studies performed:
|Forage||CT g/kg dry matter|
|Quercus semecarpifolia (himalayan oak)||170|
|Quercus robur (Swedish oak)||78|
Several studies suggest that the amount of tannins in leaves varies over the seasons and peaks in mature autumn leaves, so the figures are just to get an estimation.
How bad is a goat emitting 10 liters of methane a day? At a methane density of 0.656 g/l, that means 6.56 grams/day. Converting with a carbon dioxide equivalent of 25 for methane gives 164 grams of CO2/day, which is about what a medium car emits on a 1 km ride, or what burning 0.7 dl of petrol emits, like running a chainsaw for 3-5 minutes.
So what all this sums up to, is that a goat can be made into a farting climate culprit when fed with the wrong stuff, but keeping the feed varied and close to the goats natural supply will drastically reduce methane emissions and keep the goats healthy, while minimizing losses in energy uptake.
The goats will still emit some methane, but the carbon emitted will come from the current coal cycle and can be compared to burning wood, in contrary to other methods of keeping the landscape open and diverse, as clearing with fossile fueled machines. If the goats provides you with cheese and meat as by products, that will be a bonus for you and the climate.