We live in a greenhouse
Life on Earth depends on energy coming from the sun. About half the light reaching Earth’s atmosphere passes through the air and clouds to the surface, where it is absorbed and then radiated upward in the form of infrared heat. About 90 percent of this heat is then absorbed by the greenhouse gases and radiated back toward the surface, which is warmed to a life-supporting average of 59 degrees Fahrenheit (15 degrees Celsius).
Is the sun to blame?
How do we know that changes in the sun aren’t to blame for current global warming trends?
Since 1978, a series of satellite instruments have measured the energy output of the sun directly. The satellite data show a very slight drop in solar irradiance (which is a measure of the amount of energy the sun gives off) over this time period. So the sun doesn’t appear to be responsible for the warming trend observed over the past 30 years. Longer-term estimates of solar irradiance have been made using sunspot records and other so-called “proxy indicators,” such as the amount of carbon in tree rings. The most recent analyses of these proxies indicate that solar irradiance changes cannot plausibly account for more than 10 percent of the 20th century’s warming.
Global warming and livestock – An Introduction.
Methane (CH4) is the second most important greenhouse gas after carbon dioxide and contributes 16% of the total greenhouse gas emissions globally due to human activities. The global warming potential of methane is 21times more than carbon dioxide. Methane production from ruminants has been considered as the single largest source of anthropogenic CH4 behind the rice fields. Livestock release methane as part of their natural digestive processes. The rumen serves as the habitat of billions of microbes, including bacteria, methanogens, protozoa, and fungi which breakdown feed to produce volatile fatty acids (VFAs), carbon dioxide, ammonia, and methane. The VFAs are utilized by animals as energy source whereas gases are emitted by eructation through the mouth and also from the rectum . Cattle can produce 250–500 liter of methane per day per animal and generally lose 2–15% of their ingested energy as eructated methane. When these methane emissions are applied to the number of cattle in the world the total emissions from cattle is equivalent to about 15% of global methane emissions and about 100 million tons of methane is produced in a year .so a good way to reduce the global methane emissions is to decrease the emissions from cattle and particularly from cows. Nevertheless, controlling methane losses from ruminants has environmental as well as economic benefits. Less methane means a lower concentration of greenhouse gases in the atmosphere. Also, less methane means increased efficiency of livestock production and increased income for farmers. A greater amount of methane production can be controlled by modifying the composition of the animal feed. Changing the feed composition, either to reduce the protein percentage which is converted into methane or to enhance the meat and milk yield has been considered as the most efficient methane reduction strategy. Enhancement in the overall quality of animal feed may prove helpful in maintaining meat and dairy production at the same level with fewer animals and so less total methane emission.
Methane is released into the atmosphere both by natural (for example wetlands) and anthropogenic sources (rice fields, biomass, ruminants, etc). Mitigating methane (CH4) losses from ruminants is generally required to minimize global greenhouse gas emissions and to enhance animal performance by improving feed conversion efficiency. The contribution to the methane emission of monogastric animals such as pigs, poultry, rabbits, etc., is very low compared with the ruminant contribution. So it is important to study and try to decrease the emissions from cattle because ruminant livestock can produce between 250 and 500 L of methane per day.
Energy losses and methane production in the digestive tract of ruminants:
The synthesis of the methane in ruminants reflects energy lost and it is due to the reduction of the carbon dioxide by methanogenic bacteria. After the feed is digested in the rumen, some of the energy is lost in the form of heat or methane, giving a production of methane-utilizing between 11 and 13% of the digestible energy
Roughages (Forage type and quality):
The composition and quality of forage along with the level of intake significantly influences the rumen fermentation. Ruminants fed low-quality roughages could release a large amount of methane. Feeding crop residues to ruminants is a common practice in many Asian countries due to which methane emission from ruminants especially cattle is significant. 15% reduction in methane production by increasing the digestibility of forages and 7% by increasing feed intake. Grinding and pelleting operations of roughages decrease methane production by improving passage rate and reducing the time of feed. The shifting of animals from low to high digestible pasture significantly reduced methane production per gram of live weight gain. The use of forages meant for improving animal performance can reduce methane emissions per unit of feed intake. Importantly, pasture improvement can be a good choice if fewer animals are used
The methane production differs depending on the different types of carbohydrates that are fermented. The fermentation of cell wall fiber will lead to the production of a higher proportion of acetic acid in the rumen. As a contrast, starch fermentation gives a higher proportion of propionic acid due to the lowered pH in the rumen which causes changes in the ruminal micro-flora by an increase of amylolytic microbes and decrease of cellulolytic microbes.
The end products of the fermentation the Volatile Fatty Acids (VFA) are mainly acetate, propionate, and butyrate, we can also find valerate, isovalerate, isobutyrate, and caproate but in very low proportions. They are also the main source of energy for the ruminants, and this energy is used by the lactating cow to produce milk and body fat, but not all VFA have the same degree of efficiency. The propionic acid fermentation is more efficient in the use of the energy than acetic and butyric acids that have a large loss of methane. The type of VFA produced by the animal influences the release of methane and hydrogen, increasing the release of methane when the relation of ruminal VFA [acetic acid+butyric acid]/propionic acid increases there is a negative correlation between the proportion of concentrate and methanogenesis. A significant reduction in methane production was reported in young bulls fed with the diet containing more than 40% starch. A diet comprising 45% starch decreased methane production by 56% compared to diets containing 30% starch without affecting animal health.
Inclusion of starch in the diet has a significant impact on changing ruminal pH and microbial populations.
As concentrate contains more soluble substances, the addition of concentrate in animal diet changes the composition of
partial short-chain fatty acids (SCFA) from higher to lower acetate production and more propionate. Similarly, milk quality is negatively affected if concentrates exceed 50% which limits the use of concentrates to lower methane emissions in the dairy sector.
Cereal grains with a high proportion of starchy endosperms like wheat, barley or oats have an easier and faster fermentation giving less methane than those that have a lower proportion like maize, and sorghum.
Lipids and lipid-rich feeds are among the most efficient and emerging options for methane mitigation. Lipid inclusion in the diet reduces methane emissions by decreasing fermentation. Saturated medium chain fatty acids, C10-C14, also lead to methane reduction. At ruminaL temperature, an increasing chain length of medium chain fatty acids seems to reduce their efficiency in inhibiting methanogens and methane formation due to lower solubility reviewed the practical application of lipids to reduce methanogenesis. Oil supplementation to diet decreased methane emission by up to 80% in vitro and about 25% in vivo. The toxic effects of certain oils on rumen protozoa contributed to reduced methane production. The addition of canola oil at 0%, 3.5% or 7% to the diets of sheep reduced the number of rumen protozoa by 88–97%. The detrimental impact of unsaturated fatty acids has also been reported. Coconut oil as a more effective inhibitor followed by rapeseed, sunflower seed, and linseed oil.
The inclusion of sunflower oil to the diet of cattle resulted in 22% decrease of methane
emission. However, fats and oils may pose numerous negative impacts to the animals. Dietary oil supplementation caused lower fiber digestibility. High cost and the negative impact on milk fat concentration are some of the limitations of oil supplementation.
Miscellaneous activities to reduce methane emission:
Increased milk yield:
The milk yield also influences the production of methane, when milk yield increases, the methane per kilo milk decreases. This is logical and can be explained by the fact that the energy needed for maintenance is considered approximately the same for the animal irrespective of production level. The methane production that originates from maintenance needs is therefore also estimated to be the same for an individual animal of a specific weight. When the milk yield increases, the DMI also increases but not in the same proportion. With the increased milk yield, there is more milk to carry the “burden” of maintenance needs and methane per kg milk will decrease. Thus, with increased milk yield the methane produced in absolute terms will increase somewhat but the methane per kg milk will decrease.
Using of feed additives:
Some additives like ionophores and particularly monensin have been studied. Monensin is a broad spectrum antibiotic obtained from the actinomycete Streotomyces cinnamonensis used in some countries. It is not allowed in the European Union but it is used in the United States. Its main action is to change the fermentation from acetate to propionate which leads to the decrease of methane production. However, the widespread use of antibiotics can lead to future problems with bacteria that are resistant to antibiotics and the environmental and economic advantages of using antibiotics to decrease methane production must be weighed against the negative health effects of increased resistance.
Feed intake level:
The level of intake can also affect methane production when an animal increases its intake, the percentage of gross energy lost in the form of methane decreases
The role of human activity
In its Fourth Assessment Report, the Intergovernmental Panel on Climate Change, a group of 1,300 independent scientific experts from countries all over the world under the auspices of the United Nations, concluded there’s a more than 90 percent probability that human activities over the past 250 years have warmed our planet.
The industrial activities that our modern civilization depends upon have raised atmospheric carbon dioxide levels from 280 parts per million to 400 parts per million in the last 150 years. The panel also concluded there’s a better than 90 percent probability that human-produced greenhouse gases such as carbon dioxide, methane, and nitrous oxide have caused much of the observed increase in Earth’s temperatures over the past 50 years.
They said the rate of increase in global warming due to these gases is very likely to be unprecedented within the past 10,000 years or more.
Authors: Naila Riaz, Maryam Saleem and Hafiz Hasnain Ayoub
DVM Scholars, The Islamia university of Bahawalpur, Pakistan.