The principle of nutrition regulation technology to reduce methane emissions is: to optimise the concentrate to forage ratio in diet by controlling the crude fiber content of the diet or the fermentation process to reduce methane emission while ensuring normal production performance of ruminant animals without increasing production cost. This way, the rumen fermentation pattern or rumen microbial populations (such as methanogens, ciliates) and pH characteristics are altered to reduce methane emissions. At present, nutritional regulation is one of the most feasible approaches to reduce methane emissions and much research is being carried out to reduce methane emissions by changing the concentrate to forage ratio in diet.
Feed optimisation is one of the technologies that can be considered as part of livestock management. An overview of livestock management and related technologies is given in the article 'Livestock management'.
The methane emissions of ruminant animals are a result of their unique digestive systems. Their stomach can be divided into rumen, reticulum, omasum and abomasum. Lyford (1988) reported that the rumen volume of an adult bovine is about 56.9L, generally occupying the left half of the entire abdominal cavity, and taking up 78% to 85% of the stomach’s total volume (Li, 2007). After the feed enters the rumen, carbohydrates (mainly composed of crude fibers) in the feed are converted into carbon dioxide and hydrogen after a series of fermentation and decomposition steps by anaerobic microbes, which are then used by methanogens to generate methane as substrate. The amount of methane emissions is mainly affected by feed type, feed intake, ambient temperature, rate of consumption of feed, the balance of nutrients in the feed for microbial growth and the balance of micro-organisms that develop (bacteria, protozoa and fungi) which largely depend on the chemical composition of diet (Ding, 2007).
The diet of ruminant animals (mainly cattle, sheep, buffalo, camels, etc.) is primarily made up of forage and concentrate. Forage mainly refers to grass or hay with crude fiber content over 18%, most commonly including corn straw, alfalfa, and silage. Forage provides the animals with crude fiber, which plays an essential role in maintaining normal rumen fermentation, providing body energy and sustaining normal microbial flora, as well as promoting the synthesis of milk fat by the milk cow. At the same time, concentrates mainly supply the animals with protein, fat, minerals, and vitamins. Therefore both forage and concentrate are necessary for ruminant animals. Moreover, the ratio of concentrate to forage in diet will substantially affect the ruminant animal’s growth performance, rumen’s fermentation function, methane emission, and health condition.
Generally, when the proportion of forage feed is larger, the cellulolytic bacteria proliferate, and acetic acid fermentation is the dominant fermentation type in rumen with a large amount of hydrogen produced. As a consequence, partial pressure of hydrogen increases, which stimulates the massive proliferation of methanogens, with an increase in methane emissions. When soluble carbohydrates or starch are fed, i.e., the proportion of dietary concentrate increases, then rumen pH values decline, thereby inhibiting the propagation of methanogens and ciliates, while increasing propionic acid production (Demeyer and Henderickx, 1967). Since propionic acid fermentation consumes hydrogen, which reduces the raw materials needed for methane formation, methane emissions are lowered. An appropriate increase of the proportion of concentrate in the ruminant animals’ diet can increase the proportion of propionic acid in rumen, while reducing the content of acetic acid, and improving feed utilisation efficiency and production performance of animals. Propionic acid is mainly converted into body composition by the liver, and then it provides energy for breeding, growth, milk production, and meat production. Methane emissions and propionic acid production are negatively correlated (Church, 1979). Hence, controlling the concentrate and forage ration can not only reduce the amount of methane emitted, but also improves the production performance of ruminant animals.
There are constraints in promoting methane emission reductions by changing the proportion of fine feed to forage feed in daily diet. First, the concentrate to forage ratio in daily diet refers to the proportion of the dry matter contained, and the actual feed intake of animals may not be consistent with the calculated proportion. Secondly, corn stalks are not palatable to animals, so the ammonia treatment or silage process is necessary, and there should be a process of adoption. Thirdly, methane emissions may increase if the proportion of dietary concentrate is out of suitable range (40% to 50%) (Sun et al., 2008). Furthermore, farm management sees no direct benefits in methane reduction. There is therefore a need to explore new financial mechanisms under climate conventions to encourage the application of feed optimisation for reducing the methane emissions.
The production of methane during rumen fermentation is a necessary byproduct, which can not be completely eliminated. The control of concentrate to forage ratio in ruminant animals’ daily diet to reduce methane emissions has certain advantages and disadvantages.
Advantages of straw ammonisation
- There is no additional cost of methane reduction.
- Methane reduction and improvement of productivity could be consistently realised.
- The technology could be applied in any animal production system by using feed optimisation.
Disadvantages of straw ammonisation
- Improper ratio of concentrate to forage feed may result in abnormal rumen fermentation and increase of CH4 production.
- The technician is required to produce the best possible results of feed optimisation.
- Monitoring the characteristics of the forage and concentrate is required.
The regression relationship between 4% fat corrected milk (FCM), yield (Y) and grain supply (X) has the equation Y=1.962X + 3.492. This indicates that with every additional 1kg of grain feed intake, the milk production could increase by 2kg.
For analysis of economic benefits brought by reducing methane emissions of ruminant animals through changing the concentrate to forage ratio, the case study of Na (2010) in a small (30 cows) dairy farm is considered. In this study, 12 healthy Chinese Holstein dairy cows with average weight of 525 ± 40kg were selected as test animals. The average age of test animals was 3.5 years old. Animal groups were randomly allocated to three different rations (Rations A, B and C) featuring different forage types and concentrate to forage ratios (CTFR). On dry matter (DM) basis, Rations A and B had 40:60 CTFR whereas Ration C had 60:40 CTFR. The forage ingredient for Ration A was corn stalk. The forage component for rations B and C was corn silage. The animals in each dietary regimen were fed fixed amounts daily, consisting of 5.33±0.05kg, 4.83±0.26kg, and 7.63±0.29kg head-1 d-1 of concentrate and 8.10±0.07kg, 27.75±0.07kg, and 18.58±0.28kg head-1 d-1 of forage for rations A, B and C respectively. The concentrate was delivered twice daily and the forage was delivered three times daily. The cows had free access to drinking water at will, and they were milked twice a day. The results show that the methane outputs of Ration A, B and C were 353, 283, 263 kg head-1d-1, respectively. Ration A differed significantly from Ration B and C (p ▪ 0.05), while rations B and C show no significant difference (p ▪ 0.05). The milk yield of the three feed regimes are 10.73,12.56,12.97 kg head-1d-1, respectively. The milk production of rations B and C increased by 17.05% and 20.88%, respectively, compared to Ration A. Ration C increased by 3.26% compared to Ration B, without anomalies detected in rumen fermentation. Analysis of specific economic benefits is presented in figure 1.
TABLE --> FIGURE 1
From figure 1, since there is a need for corn stalk chopping in Ration A, the labour cost of this diet is higher than the other two rations. The daily profit per cow per day of Ration C increases by 4.3 yuan compared to Ration B, with a reduction of methane emissions by 7%. The methane production for each kg of milk decreases with the increase of the proportion of dietary concentrate.
There are considerable potentials to improve animal production performance such as yield per unit, and to reduce methane emissions by using feed optimisation techniques. Many experimental tests have shown that with the improvement of feeding technology, methane emissions per unit of livestock is reduced (You, 2007; Na, 2010).
It is reported that when daily milk production increases from 25kg to 30kg, then the methane emissions per unit milk product decreases by 10% (Yang, 2000). When the average daily gain increases from 0.65kg to 0.8kg, the methane emitted per unit of weight gain can be reduced by 14%. According to the Na (2010) studies, when milk yield of milk cow increases from 11kg to 13kg, the methane emission per unit of milk product decreases by around 39%.
The regression relationship between methane production per unit of FCM and grain supply was expressed as Y=-2.546X + 46.442. This also indicates that with every additional 1kg of cereal feed intake, the methane emission per kg of FCM can be reduced by about 2.5 litres.
See the section on economic development above.
Church (1988): Digestive physiology and nutrition of ruminants. Englewood Cliffs: Prentice Hall.
Demeyer, Henderickx. (1967): The effect of C18 unsaturated fatty acids on methane production in vitro by mixed rumen bacteria. Biochimica et Biophysica Acta (BBA) - Lipids and Lipid Metabolism, 137 6:484-497.
Ding, X.Z. (2007): Effect of Tannic Acid on in Vitro Rumen Fermentation Characteristics and Methane Emission of Sheep. Dissertation, Gansu Agriculture University (in Chinese).
Li, J.G. (2007): Modern dairy cattle production. Beijing: China Agriculture University Press, 169 (in Chinese).
Lyford, S.L. (1988): Growth and development of the ruminant digestive system. The ruminant animal. Digestive Physiology and Nutrition, Church D.C. edited, Prentice Hall.
Na, R.H. (2010): Effects of Diet Composition on Methane and Nitrogen Emissions from Lactating Cattle. Dissertation. Beijing: China Academy of Agriculture Sciences (in Chinese).
Sun, D.C., Zhao, Z.L. and Wei, M.L. (2008): Effect of different concentrate to forage ratio of TMR to dairy cattle rumen indices. Feed Research, 10, 47-50 (in Chinese).
Yang, S. R. (2000): Reducing methane emission of cattle from biology prospect. Agro-environment and Development, 1:47-48 (in Chinese).
You, Y.B. (2007): Studies on Methane Emission Measurement and Predicting Model of Beef Cattle. Dissertation. Beijing: China Academy of Agriculture Sciences (in Chinese).