Reducing Rumen Methane to Improve Feed Efficiency and Counter Climate Change

Climate Change

Climate change is the great environmental issue of our time. The vast majority of climate scientists agree that the increased concentration of "greenhouse gasses" (GHGs) in the Earth's atmosphere is responsible for the increase in global temperature since the early 1900's. The principle GHGs are carbon dioxide, methane, and nitrous oxide. They warm the atmosphere by trapping energy which is radiated by the earth and which would otherwise be dissipated into space. Scientists are confident that human activities have contributed most of the additional GHGs, and that their annual production must be reduced to prevent catastrophic changes to our environment. In Canada, agriculture contributes 8.3% of overall GHG emissionsi human activities.

Why Methane from Cattle is Important

Although carbon dioxide (CO2) is the dominant GHG, methane (CH4) is much more potent, with a global warming potential 30X times greater than CO2 , per gram. In Canada, cattle contribute about 70% of overall agricultural methane emissions, with most of it coming from the rumen. This translates into about 40% of overall GHG1 emissions by agriculture. So even a modest reduction in the rate of methane production by cattle would have an important positive effect.

How Cattle Produce Methane

Cattle and other ruminants have a well-developed ability to utilize high fiber diets, thanks to symbiotic microbes in the rumen. Humans benefit from this as beef cattle play a vital role in converting high fiber feeds like hay (otherwise unusable by humans and other simple stomached animals) into large volumes of high quality meat protein. Since much of the land which is used to feed beef cows is not suitable for producing grains or oilseeds, the cows are consuming little food that could be used directly by humans. However, cattle are also a major source of methane. Most of it is produced by rumen microbes as a by-product of digestion, and exhaled by the animal. A much smaller source of methane is from the breakdown of manure.

Reducing Rumen Methane

Methane is not only bad from an environmental perspective, but it represents a 3-10% loss of energy (CH4 is a major part of natural gas) from the digestive process. Reducing methane emission from the rumen would not only reduce GHG production, but could also result in more efficient use of feed energy by the animal. So strategies for methane reduction also have the potential to reduce feed costs

A number of methods to reduce the amount of methane produced in the rumen have been explored. They include various feed additives, adjusting the intake level and quality of forages, and manipulating the rumen microbe population. However, many of the beneficial effects which have been found diminish over time as the rumen microbes adapt to the new conditions. Other methods employ compounds which are themselves harmful to the environment, while some of the effective compounds have a negative impact on productivity.

A recent experiment by Penn State's Alexander Hristov and collaboratorsii examined the use of a novel methane inhibiting compound, 3-nitroxypropanol (3NOP), in lactating Holstein dairy cows. The cows were fed a diet based on corn silage and alfalfa haylage. The 48 animals were assigned to one of four groups: 1. Control (0mg/kg); 2. Low Rate (40mg/kg); 3. Medium Rate (60mg/kg); and 4. High Rate (80mg/kg). The 3NOP was mixed with propylene glycol as a carrier, with all groups receiving the same amount of glycol.

The information collected over the 12 week trial included typical productivity measures such as feed intake, milk yield, milk fat, feed efficiency and body weight. Cow breath gas samples were obtained at 2 to 4 week intervals and analysed for methane, carbon dioxide and hydrogen1. Methane emissions were dramatically reduced with the addition of 3NOP to the diet (Fig. 1.). Compared with the control group, addition of 3NOP reduced methane emission by 25%, 31% and 32% for the 40mg/d, 60mg/d and 80mg/d diets, respectively. Carbon dioxide emissions were not affected by 3NOP.

Breath Emission of Methane by Dairy Cows Fed Levels of 3-Nitroxypropanol

Figure 1. Breath Emission of Methane by Dairy Cows Fed Levels of 3-Nitroxypropanol.

Some of the productivity results are presented in Table 1. There were no significant differences for dry matter intake, energy corrected milk yield, milk fat% or milk true protein%. However, body weight change for the 3NOP groups was greater than the control group, on average gaining weight 80% faster over the 12 week trial.

Table 1. Effect of 3-nitroxypropanol on productivity measures of dairy cows.

 
Diet
Probability of an effect*
Measure
Control
Low 3NOP
Med. 3NOP
High 3NOP
Control vs all Trts1
Linear effect2
Dry matter intake (kg/d)
28.0
28.0
27.7
27.5
>.10
>.10
Energy corrected milk yield (kg/d)
44.9
45.2
46.2
43.9
>.10
>.10
Milk fat (%)
4.08
3.98
4.02
4.25
>.10
>.10
Milk true protein (%)
3.06
3.14
3.12
3.13
.07
>.10
Body weight change (g/d)
210
353
451
330
.05
.09

*only probability values ≤.10 are shown

1 comparison between the control group and pooled effect of the treatment groups

2 Effect of level of 3NOP in diet on measures. (eg. Does dry matter intake vary with the amount of 3NOP in the diet in a linear (straight line) manner?

The Future

While research into using 3-nitroxypropanol is at a very early stage, it shows definite promise as a potential means of reducing methane emission by cattle. Although this initial experiment was with dairy cows, rumen function in beef cows is quite similar. An encouraging aspect from a beef industry perspective is the increase in cow weight gain which accompanied the reduction in CH4 emission. This indicates that at least some of the energy which would have been lost in the production of methane gas was captured by rumen microbes and retained by the cow. And although the process of weight gain by lactating cows is somewhat different than that of growing cattle, it seems likely that 3NOP could have a similar positive effect.

Although 3NOP has to be supplied to the rumen on a daily basis, it should be relatively easy to add to a feedlot ration where a concentrate mix is fed. For animals fed only stored forages or grazing on pasture, it may be possible to add it to salt or mineral, or perhaps in the form of a slow release rumen bolus.

Many more trials are needed to verify these results and to test the additive over a wide range of cattle types and conditions. Safety for animals and people will also have to evaluated before the 3NOP could be considered for certification as a commercial product. But this experiment shows it does have potential and that it is possible to reduce the methane output of ruminants with minimal effect on performance.

1The hydrogen measurement was related to mode of action of 3NOP.

References

iNational Inventory Report 1990-2013: Greenhouse Gas Sources and Sinks in Canada -Executive Summary https://www.ec.gc.ca/ges-ghg/default.asp?lang=En&n=5B59470C-1&offset=4&toc=show
iiHristov, AN et al (2015). An inhibitor persistently decreased enteric methane emission from dairy cows with no negative effect on milk production. PNAS 112 (34): 10663-10668.


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