Effect of sulphur and calcium nitrate on methane production by goats fed a basal diet of molasses supplemented with Mimosa (Mimosa pigra) foliage

Phonevilay Silivong, T R Preston* and R A Leng**

Faculty of Agriculture and Forest Resource, Souphanouvong University,
Luang prabang, Lao PDR
silipvl@yahoo.co.th
* UTA (Colombia), AA 48 Socorro, Santander, Colombia
** University of New England, Armidale NSW, Australia

Abstract

Four weaned crossbred goats (Bach thao x local female),  with an initial body weight of 10.5± 2.5 kg and 4-5 months of age, were assigned to a 2*2 factorial design in a 4*4 Latin square to compare the effect on rumen methane emissions, digestibility and nitrogen balance on a basal diet of molasses and Mimosa (Mimosa piga) foliage, supplemented  with NPN from calcium nitrate or urea, and sulphur (0.8%) from sodium sulphate.

Supplementing the basal diet with calcium nitrate led to a reduction in the methane/carbon dioxide ratio in the eructed breath of the goats compared with control animals supplemented with urea. The addition of sodium sulphate to the diet also reduced the methane/carbon dioxide ratio, with the two supplements having additive effects. Added sulphate increased both digestibility of crude protein and N retention. These criteria were not affected by the NPN source.

Key words: Digestibility intake, NPN, N retention, sodium sulphate, urea

Introduction

Livestock contribute some 18% of greenhouse gases according to Steinfeld et al (2006). Enteric methane from fermentative digestion is the main source of these emissions. There is an urgent need to develop ways of reducing methane emissions from ruminants in order to meet future targets for mitigating global warming. From a survey of the relevant literature, Leng (2008) concluded that the presence of nitrate salts in the rumen will act as a competitive sink for the hydrogen produced by fermentation of carbohydrate such that it is converted to ammonia rather than methane. Trinh Phuc Hao et al (2009) showed that nitrate could be safely fed as the major source of fermentable N provided the animals (goats) were adapted to the diet over a period of 2 weeks. In their experiment, N retention was the same with nitrate as with urea as the source of fermentable N. Results of recent research in Australia (Nolan et al 2010) showed that the production of methane in the rumen gas of sheep fed oat hay was reduced by 25% by feeding potassium nitrate instead of urea as the nitrogen source. 

Leng (2008) proposed that the conditions favouring the action of nitrate in reducing methane production were: a highly fermentable source of energy,  a protein source which would mainly escape the rumen fermentation (eg: bypass protein; see Preston and Leng 2009) and an additional source of sulphur.  Leng and Preston (2010) reviewed the research of Van Zijderveld et al (2010) and concluded that: “the CH₄ suppressing effects of nitrate and sulphate were independent and additive”.

Molasses is a source of highly fermentable carbohydrate (contains > 50% soluble sugars) and is very low in crude protein (<0.5% in DM). When mixed with urea and supplemented with cassava foliage it supported high growth rates in fattening cattle (Ffoulkes and Preston 1978).  

Mimosa pigra is an invasive weed of the genus Mimosa in the family Fabaceae. This plant is considered to be one of the worst environmental weeds of the Mekong River basin (Storrs et al 2001). In Tram Chim National park in Dongthap Province in the Mekong delta, there is growing concern over the rapid growth of the Mimosa pigra plant, that has taken over more than one seventh of the 7,600 ha of the park (Tran Triet et al 2007; Viet Nam-VNS). However, recent research (Nguyen Thi Thu Hong et al 2008) has shown that mimosa foliage is an excellent feed for goats, supporting growth rates when given as the sole feed of almost 100 g/day. It was hypothesized that the presence of condensed tannins would confer bypass properties on the protein in the Mimosa and that this could explain its high nutritive value.

The objective of the present study was to compare the effect on rumen methane emissions, digestibility and nitrogen balance of goats given a basal diet of molasses and Mimosa  foliage, supplemented with NPN from calcium nitrate or urea and additional sulphur from sodium sulphate.

It was hypothesized that the Calcium nitrate would reduce methane emissions and that there would be a synergistic effect of giving additional sulphur.

Material and methods

Location and duration       

The experiment  was conducted in the experimental farm of An Giang University in Vietnam, from September through October 2010.

Animal and housing

Four crossbred weaned goats (Bach Thao x local female) with initial body weight of 10.5± 2.5 kg and 4-5 months of age were used.  (Photo 1)  There were housed individually in metabolism cages made from bamboo (dimensions of width 0.8 m, length 1 m and height 0.8 m) and designed to collect separately feces and urine.

Photo 1. Goats confined in the metabolism cages

Experimental treatments and design

Four treatments were arranged in a 2*2 factorial design in a 4*4 Latin square with 10 days per period: 5 days for adaptation and 5 days for collection of feed refusals, feces and urine. The factors were:

·         Source of NPN: Calcium nitrate or urea

·         Supplementary sulphur: 0 or 0.8% S in the diet DM as sodium sulphate. 

Individual treatments were:

·         U:  Urea as source of NPN (2% of diet DM)

·         US: same as Urea but with 0.8% added sulphur as sodium sulphate

·         CN:  N from calcium nitrate (3.8% of diet DM)

·         CNS: Same as CN but with 0.8% added sulphur as sodium sulphate

The basal diet was molasses and mimosa foliage both offered to appetite. The molasses was diluted to 20 Brix (20% DM) before dissolving in it the urea or nitrate and sodium sulphate. The diluted molasses was offered 3 times daily (7.00 am, 12.30am and 5pm).

Feeding and management

The Mimosa was collected daily from natural stands in the University campus (Photo 2) and was hung in bunches above the feed trough. Molasses was fed in a plastic bucket. Feeds offered and residues were weighed every morning. 

Photo 2. Mimosa pigra

Measurements

Live weight was recorded in the morning before feeding at the beginning and end of each period. Feeds offered and refusals  were collected daily during the 5 days of the collection period. Urine was collected in buckets with 20 ml of a solution of sulphuric acid (10% sulphuric acid concentrate + 90% distilled water). Feces were collected daily and stored at -18ºC and, at the end of each period, sub-samples were mixed together and ground with a coffee grinder. Ratio of methane and carbon dioxide was measured at the end of the 2nd and 4th  period, 2h after feeding in the morning

Chemical analyses

The sub-samples of feed offered and refused and of feces were analysed for DM, N and ash according to AOAC (1990) methods. A sample of rumen fluid was taken by stomach tube on the last day of each period 2h after feeding in the morning. The pH was measured immediately with a glass electrode and digital pH meter. A drop of concentrated sulphuric acid was then added to preserve the samples prior to analysis for ammonia by steam distillation (Nguyen Van Lai and Ly 1997). Ratio of methane and carbon dioxide was measured by Gasmet meter (Photo 3).

Photo 3. Goats were confined in a closed space for the measurement of the eructed gases with the Gasmet equipment

 Statistical analysis

The data were analyzed by the General Linear Model option in the ANOVA program of the Minitab Software (version13.2). Sources of variation in the model were: treatments, periods, animals and error.

Results and discussion

Crude protein in mimosa foliage was high contrasting with the very low values in molasses (Table 1).

Intake of mimosa foliage was not affected by sources of NPN or sulphur (Table 2). However, molasses intake was lower when sulphate was fed and when urea rather than calcium nitrate was the source of NPN. Sulphur dioxide is added to sugar cane juice during the extraction of sucrose from sugar cane and ends up as suphate in the molasses at a final concenration equivalent to about 0.4% S in the molasses. It is possible that the goats reduced their intake of molasses when suphate was added, due to the increased bitter taste when supplementary sulphate was also given. There is no explanation for the higher intake of molasses when urea was fed unless the goats could detect the taste of the calcium nitrate. Total DM intake was not affected by sulphate supplementation but was higher when urea rather than nitrate was the NPN source.

Apparent coefficients of digestibility o f DM and OM did not differ among treatments (Table 3). In contrast, coefficients for crude protein were higher with supplementary sulphur and for nitrate compared with urea. Daily N retention, and N retention as per cent of N intake and of N digested, were higher with added sulphur but were not affected by the NPN source.  

Figure 1. Effect of sodium sulphate on N retention as per cent of N intake in goats fed molasses supplemented with mimosa with calcium nitrate or urea as source of NPN	Figure 2. Effect of sodium sulphate on N retention as per cent of N digested in goats fed molasses supplemented with mimosa with calcium nitrate or urea as source of NPN

There were no difference among treatments in rumen pH  and NH₃, but ratio of methane to carbon dioxide in eructed air was decreased by supplementation with sulphate and by replacing urea with calcium nitrate (Table 4 and Figures 3 and 4).

Figure 3. Effect of NPN source on ratio of methane to carbon dioxide in eructed gas from goats fed molasses and mimosa forage with and without added sodium sulphate	Figure 4. Effect of added sulphate on ratio of methane to carbon dioxide in eructed gas from goats fed molasses and mimosa forage with calcium nitrate or urea as source of NPN

These results agree with the findings of Van Zijderveld et al (2010) who measured methane and carbon dioxide production (in respiration chambers) by sheep fed maize silage supplemented with urea, nitrate and sulphate or nitrate plus sulphate. 

Leng and Preston (2010) showed that the observed reduction in methane production in the experiment of Van Zijderveld et al (2010a) could be predicted from the change in the ratios of methane and carbon dioxide (Table 4). Applying this same approach to the methane/carbon dioxide ratios recorded in the present experiment showed degrees of reduction of methane broadly similar to those observed by Van Zijderveld et al (2010a) (Table 6 and Figure 5) wsith additive effects for nitrate and sulphate.

Figure 5. Effect of added sulphate and nitrate and sulphate plus nitrate on per cent reduction in methane in the present experiment and that reported by Zijderveld et al 2010

Conclusions

• Supplementing a diet of molasses and mimosa foliage with calcium nitrate led to a reduction in the methane/carbon dioxide ratio in the eructed breath of goats compared with control animals supplemented with urea. Adding 0.8% sulphur as sodium sulphate to the diet also reduced the methane/carbon dioxide ratio, with the two supplements having additive.effects.

• Supplementary sulphate increased both digestibility of crude protein and N retention. These criteria were not affected by the NPN source.

Acknowledgments

The authors gratefully acknowledge the Mekarn project, financed by Sida,  for supporting this research. Staff members and students of An Giang University are thanked for their assistance in the preparation of the experimental facilities and for help in the laboratory.

References

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Received 15 January 2011; Accepted 15 February 2011; Published 6 March 2011

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