Mitigation of methane emission by means of oil and nitrate supplement in diets of growing cattle

Tran Hiep, Dang Vu Hoa* and Nguyen Xuan Trach 

Faculty of Animal Sciences and Aquaculture – Hanoi University of Agriculture – Vietnam: hiep26@yahoo.com
^*Nation Institute of Animal Sciences – Hanoi – Vietnam

Abstract 

The objective of the study was to determine methane emission and to mitigate methane emission by oil and nitrate supplement in the diets of growing cattle. An experiment was carried out during 3 months (June - August) in the experimental station of Hanoi University of Agriculture (Vietnam). Twenty-two growing cattle (170 kg on average) were equally divided 8 blocks corresponding to 8 diets based on 2% NaOH treated rice straw and cassava leaf meal (1% BW, DM basic), supplemented with 1.5%, 3.0%, 4.5%, 6.0% sunflower oil plus 4%CaNitrate or 1.5% urea as NPN source. Methane emission was determined by using CH4/CO2 ratio method. 

Methane emission rate (L/kg DMI) was reduced by 26% by nitrate supplement compared with urea supplement. The increase in oil level reduced non-linearly methane emission. The best level oil supplement was 3.0%. However, the best treatment was found with 4% CaNitrate and 1.5% oil supplement in the diet. It was also shown that estimated energy loss from the experiment diet ranged from 5-8% diet gross energy, compared with around 12% potential energy loss from diet without supplement. As a conclusion, it should be added nitrate and oil supplement (at a limit of 1.5%) to mitigate methane emission from growing cattle.   

Keywords: Growing cattle, methane mitigation, nitrate, oil.  

Introduction 

Ruminants are an important source of methane emission to the atmosphere, improving the greenhouse effect. They contribute about 22% of the total anthropic sources in the world, or 80 Tg/year (USEPA 2000). Methane production results from the digestive process of herbivore ruminants in the rumen, during anaerobic fermentation of soluble and structural carbohydrates, mainly in grass forage, and corresponds to an energy loss of around 6% (in temperate climate) or 10% (in tropical climate) of gross energy intake (USEPA 1990).  

Nevertheless, understanding the relationship of diet to enteric methane production is essential to reduce uncertainty in green house gas emission inventories and to identify viable green house gas reduction strategies. For cattle, reducing methane means an improvement in feed quality. Dietary changes can impact methane emissions by decreasing the fermentation of organic matter in the rumen, shifting the site of digestion from the rumen to the intestines, diverting H away from methane production during fermentation, or by inhibiting methanogenesis by rumen bacteria (Johnson and Johnson 1995; Benchaar et al 2001). Diets that restrict the hydrogen available in the rumen for methane hygienic bacteria generate less enteric CH₄. 

When rumen microorganisms ferment feed organic matter, they generate the reduced cofactor NADH which is in equilibrium with rumen H₂. In ruminants, the H₂  is normally removed by the reduction of CO₂ to form methane. However, NO₃ has a higher affinity for H₂ than CO₂ and, when it is present, H₂ is first used in the reduction of NO₃ to NO₂ and NO₂ to NH₃ thereby reducing the production of methane from CO₂. Otherwhile, some microorganisms in the rumen use H₂ to hydrogenate the double bonds of unsaturated fatty acids. Therefore, the addition of unsaturated fatty acids to the diet results in inhibition of CH₄ production.  

So, providing nitrate and oil source is expected to lesson methane production and emission from ruminant. However, interaction effect of both nitrate and oil on the methane emission of growing cattle is not well-documented, especially with typical cattle diet in Vietnam.  

Materials and methods

Location

The in vivo experiment was done at the experimental farm of Faculty of Animal Sciences and Aquaculture, Hanoi University of Agriculture (FASA-HUA).

Animals

Experiment involved 24 growing cattle of around 170 kg. Each cattle was housed in a tie-stall to allow intake and methane measurement.  

Diets

Experimental diets much be representative for most dairy systems, diets were thus formulated using main forages and by-products in northern Vietnam. The basal diet includes: NaOH treated rice straw ad lib + cassava leaf (1%BW, DM basis). This basal diet was supplemented with 8 different levels of SF oil + NPN (urea or Ca-Nitrate) as factor reducing methane production in rumen. Eight levels of SF oil + Ca-Nitrate were as follows: 

 

Experimental design

With regard to the objective of evaluating effect of oil and nitrate on methane emission of growing cattle by using CH4/CO2 ratio method, 24 growing cattle were randomly allocated to 8 treatments (3 animals/block) based on animal’s body weight, age and sex. The treatment followed a 2*4 factorial design with Ca-Nitrate (4%DM) or urea (1.5% DM) as source of NPN and 4 levels of SF oil (1.5%, 3.0%, 4.5% and 6.0% DM). The experiment lasted for 4 weeks (one adaptation week and 3 measurement weeks).  

Intake measurement

For each cattle, the daily forage and concentrate intake were individually determined. Forage refusals were weighed the next morning. Total DMI was estimated as the difference between the total amount of feeds offered and that refused, on DM basis. 

Feed sampling procedure

Approximately 500 g on a fresh matter basis of each ingredient are collected every methane estimating day. They were then dried in a oven at 70°C for 48 h to determine DM content. All dried samples were grounded into a 1 mm screen CYCLOTEC and stored in closed plastic boxes at room temperature before chemical analyses.

Chemical composition analysis:

Chemical composition of each feed (ash, CP, NDF, ADF, starch and sugar) was predicted according to a large NIRS database and equations for tropical and temperate forages (from Gembloux (Belgium) and Cirad (France) databases).

Gas measurement and methane emission estimation:

The total methane emission was estimated for each cow using the equation developed by Madsen et al (2010) as follow:s: 

CH₄ produced (l/d) = a * (b-d)/(c-e)

where:

 

The  CH4 production can be estimated as shown above, based on known/calculated CO2 production by the animal(s), measured background concentration (outdoor concentration representing atmospheric air) of CH4 and CO2, and measured concentration of CH4 and CO2 in an air sample containing a mixture of air from background and gases excreted from the animal. The air samples were collected two days at the end of the experiment and then measured for CH4 and CO2 by Gas chromatography: GC17A, Detector FID.

 Potential methane emission estimation

The total methane production was estimated using an equation developed by Moe and Tyrell (1980): [CH4 l/j = 86.1+67.0*Cell+43.9* Hemi+12.9 * Starch and Sugar; (kg ingested/day on DM basis)].

Statistical analysis

The data were analyzed by the General Linear Model option in the ANOVA program of SAS system Software (version8.0). 

Results and Discussion 

Diet intake 

The effect of NPN source and oil level on diet intake is shown in table 3. Results show that nitrate supplement increased significantly DM, CP and fiber (NDF, ADF) intake compared with urea supplement. In fact, the nitrate supplement increased intake by 8%, 5% and 6% for DM, CP, NDF and ADF. This could be explained by low degradation of nitrate and therefore more efficient nitrogen utilization of rumen microbes in the rumen. Faverdin (2003) and Hoover & Stokes (1991) suggested that the protein use efficiency depends on protein sources and their degradation rates. A rapidly degradable protein could be underutilized because the rumen microbes could not, at the same time, depose enough energy issued from the carbohydrate fermentation process. Hence, the exceeded nitrogen could provoke digestive disorder or metabolism troubles (uraemia) and/or reduce microbial activities considerably. The nitrogen lowly reduced from nitrate is thus more important than from urea because nitrate provides the nitrogen source to microbes at the same time as the carbohydrates are fermented.  

Results show, on the other hand, no effect of oil supplement on intake was found for all variables. Beauchemin et al  (2008) assumed that most forages have some fat content and that DMI may be suppressed at fat intakes above 6 to 7%, CH4 mitigation of 10-25% are possible from the addition of dietary oils to the diet of ruminants. Machmuller et al  (2000) reported that oils offer a practical approach to reducing methane in situations where animals can be given daily feed supplements, but excess oil is detrimental to fibre digestion and productions. Oils may act as hydrogen sinks but medium chain length oils appear to act directly on methanogens and reduce numbers of ciliate protozoa. In contrast, Johnson et al  (2002) and (2008) found no response to diets containing 2.3, 4.0 and 5.6% fat (cottonseed and canola) fed to lactating cow. So, the present results are similar to those found by Johnson et al (2002 2008). 

Concerning the interaction effect of both NPN and oil supplement on intake, the higher intake was found for diets containing 4% nitrate. The highest and lowest DM intake were found for diet containing 4% nitrate plus 4.5% oil (3,36% BW) and 1.5% urea plus 6.0% oil (2.83% BW). However, the best level of protein and fiber intake seemed to be diet containing 4% nitrate plus 1.5% oil (554 g CP, 3290 g NDF and 2329 g ADF per day). As explained above, nitrate is more important than from urea due to its low rate of reduction to ammonia and suitable level of oil supplement will enhance fibre digestion.  

 

Effect of NPN sources on methane emission 

Effect of NPN source on methane emission is shown in table 4 and figure 1. Results show that nitrate reduced significantly methane emission compared with urea by 22 and 24% for total methane emission (117 vs 147 L/day) and for methane emission rate (22 vs 29 L/kg DMI or 37 vs 49 L/kg NDFi). Normally, methane emission increased with level of intake (Giger-Reverdin et al  2000). But in this case, diet supplemented with nitrate that have higher intake emitted lower methane. So, this illustrated the strong effect of nitrate on methane emission.

Ascensão (2010) found the nitrate diet produced less methane (expressed by g/kg of DMI) than urea diet (P<0.001), methane production (g/day) was 41.6% lower from bulls fed a nitrate diet than from bulls fed an urea diet (P<0.001). Methane production (% GEI) was 5.6% on urea diet and 3.1% on nitrate diet, resulting in a production of less 41.1% with nitrate diet compared with urea diet (P<0.001). According to Leng (2008), nitrate reduction in anaerobic systems occurs by two distinct pathways: dissimilatory nitrate reduction to ammonia and assimilatory nitrate reduction to ammonia. And NO3 has a higher affinity for H2 than CO2 and, when it is present, H2 is first used in the reduction of NO3 to NO2 and NO2 to NH3 thereby reducing the production of methane from CO2. In fact, 1 mol of nitrate would produce 1 mol of ammonia and reduce methane production by 1mol. As a consequence, nitrate diet reduced strongly methane emission compared with urea in our study.   

 

Effect of oil levels on methane emission

There was no effect of oil level on methane emissions (Table 5). 

 

Oils may act as hydrogen sinks but excess oil is detrimental to fibre digestion and productions (Machmuller et al  2000).  Excesss oil also cause digestive disorders and depends on animal individual response. As a result, there was no significant difference between different oil levels.   

Interaction effect of NPN and oil on methane emission

When urea was the source of NPN, it appeared that SF oil levels of 3 to 6% resulted in reduction of methane emissions (Table 6; Figure 2). On the other hand, it appeared that nitrate was most effective in reducing methane emissions when the oi llevel was only 1.5%.  

 

 

Energy loss from estimated and measured methane emission

Typically, about 6 to 10% of the total gross energy consumed by ruminants is converted to CH4 and released via the breath (Brouwer et al 1965). Johnson et al  (1993) and Kujawa (1994) found that the energy loss from methane varied from approximately 2 to 12% of GE intake, depending on diet quality.  

Estimates of energy loss from methane emission in the present study are presented in Table 7. The energy loss due to methane emission from diet without supplement, as estimated by equation of Moe and Tyrrell  (1979) varied around 12% of gross energy intake. But the energy loss from diet supplemented with NPN and oil were strongly reduced by 33-62% (52% on average), lowest in diet containing 4% nitrate + 1.5% oil (only 4.56%, 62% reduction) and highest in diet containing 1.5% urea + 1.5% oil (8.5%, 33% reduction).