Effect of different levels of supplementary potassium nitrate replacing urea on growth rates and methane production in goats fed sugar palm-soaked rice straw and mimosa foliage

Iv Sophea, Khieu Borin, R A Leng and T R Preston

Kampong Cham National School of Agriculture, Cambodia
iv_sopheakcnsa@yahoo.com

Emeritus Professor, University of New England, Armidale NSW 2351 Australia,
PO Box 361, Coolum Beach 4573
Queensland, Australia
rleng@ozemail.com.au

UTA-TOSOLY, AA 48 Socorro, Colombia
preston@lrrd.org

Abstract

Our objectives were to study the effect of nitrate-nitrogen diet on the growth performance and rumen gases change in goats fed high in rumen undegradable protein. 12 young goats were randomly allocated to four treatments and three replications. Urea were subsequently dropped and replaced by nitrate without changing exogenous nitrogen content to have four levels of nitrate (0, 2, 4 and 6%) based on dry matter intake. There was a very good improvement in feed intake as percentage of body weight (P<0.000) when nitrate levels increased. Growth performance was insignificant different (P<0.83) with urea as a sole fermentable nitrogen supplement and/ or after being completed replaced by nitrate. However, there was a tendency for goats fed nitrate to have a slightly higher weight gain than urea. The growth curve of all animals is linear when percentage of supplementary nitrate increased respectively although there were was some inconsistency in animal performance within early stage of adaptation of 21 days. Rumen ammonia content was high with 34 mg/ 100 ml for 2 and 4% of supplementary nitrate and 42.5mg/100 ml for urea level equivalent to 6% nitrate based on dry matter basis.

The results indicate that nitrate can be safely used as rumen supplementary nitrogen source as well as urea to improve animal feed intake and animal performance with another tremendous advantage of reduction of rumen methane emission.

Introduction

Farmers in developing countries are usually unable to select basal diet which can meet daily requirement of their ruminants, particularly in dry season period. FAO and IAEA (1997) have quoted that “under-nutrition due to inadequate or fluctuating nutrient supply is a major constraint to animal production in developing countries. Poor nutrition results in low rates of reproduction and production as well as increased susceptibility of livestock to disease”

Leng (1990) reported several factors affect the efficiency of utilization of poor quality roughage by ruminants for productive purposes including the availability of nutrients in the feed to support an efficient microbial growth and a high rate and extent of digestion in the rumen which in turn optimizes feed intake. The strategy for improving production has therefore been to maximize the efficiency of utilization of available feed resources in the rumen by providing optimum conditions for microbial growth and then by supplementation to provide dietary nutrients to complement and balance the products of digestion to requirement (FAO/IAEA, 1997).

Availability of rumen ammonia is often a primary deficiency in diets fed to ruminants in tropical countries. Ammonia is usually generated from degradation of dietary protein or by supplementation with non protein nitrogen. Bryant and Robinson (1962) found that 82% of bacteria strains in the rumen grew with ammonia as their principle source of nitrogen while some species of rumen bacteria use exogenous amino acids. As preformed proteins are expensive and in great demand for feeding of non ruminants, attention of researchers has turned to the possible use of non-protein nitrogen sources for ruminant feeding.

Urea has been used to feed ruminants as a source of fermentable nitrogen to increase feed intake and dry matter digestibility, microbial activity, microbial protein, and volatile fatty acids (Oh 1969; Willis 1952; Golluscio 1997). Nitrate could potentially replace urea in diets to provide a nitrogen source for microbial protein production and growth (Leng et al 2007). Hao (2009) revealed that nitrate was fed safely to goats at levels that supply all the requirements of rumen microbial protein synthesis in diets low in true protein. Growth rate and nitrogen retention was similar or even slightly better than urea when nitrate was the non protein nitrogen source.

Leng (2007) also reported that nitrate can replace carbon dioxide as an electron acceptor with the generation of another reduced product -- in this case, ammonia, i.e. nitrate is reduced to nitrite and then to ammonia, resulting in lower methane gas emission. Overall reaction

• NO3^-+2H⁺      H2O+NO2^- -------------1

• NO2^-+6H⁺    H2O+ NH3   -------------2

This experiment will be conducted due to the fact that few experiments have been done to compare urea and nitrate as sources of fermentable nitrogen for ruminants and their effect on rumen and microbial growth.  

Materials and methods

Location

The experiment was conducted in Kampong Cham national school of agriculture, about 125 km from Phnom Penh capital city, Cambodia.

Animal housing

Experimental young goats were housed separately in the bamboo cage (1*1.5 m). Water was provided freely through a bucket inside each cage and feeding trough was placed right in front of the cage (Photo 1).

Experimental design and treatment

12 young goats were individually housed in the experimental cage and fed on the basal diet of rice straw, 0.3 % water spinach, and 2% mimosa foliage as live weight basis. Rice straw was chopped and soaked with 10 % diluted sugar palm a few second before feeding freely to animals. All four treatments are isonitrogenous and levels of nitrate are from 0, 2, 4 and 6% of estimated dry matter basis.

KN0    : Urea only

KN2    : 2% potassium nitrate+ plus urea

KN4    : 4% potassium nitrate+ plus urea

KN6    : 6% potassium nitrate only

All animals were fed with the mineral cake (table 1).  

Feeds and feeding system

Water spinach, sugar palm syrup, rice straw and urea were bought from local farmers. Potassium nitrate was brought from Cantho city in Vietnam. Mimosa foliage was collected every very morning without storing overnight.

Water spinach was chopped and spayed with nitrate and/or urea solution and fed at 7.00 am to make sure that all nitrate and/or urea were consumed. Rice straw was chopped and soaked with 10% sugar palm for a few second before feeding to goats at 10.00 am, 01.00 pm, and 04.00 pm. Mimosa foliage was fed late on 2.00pm.

Data measurement

The goats were weighed every 7 days during the 84-day trial. Individual feeds and residues were recorded daily. Sample of feeds (rice straw, water spinach, and mimosa foliage) was analyzed for DM and N. In addition, the residue of feed was analyzed for DM every 7 days. Rumen fluid was collected and measured quickly for PH before analyzed for rumen ammonia.

Gas sampling

Rumen gas was collected from breathed air in glass bottle and incubation time to allow goats to breath in the bottle was 3 minutes. Gases were stored for later analysis of CH4:C02 ratio using gas meter (photo 2). T

Gas analysis

Method of analysis of gases was described in photo 3, 4 and 5

Statistical analysis

The data will be analyzed by Analysis of variance (ANOVA) using the General Linear Model (GLM) procedure of the Minitab software version 14 and covariance.

Sources of variation are goats, treatments, and error.

Results

Chemical composition of experimental diets

Feed intake and daily weight gain

Daily feed intake as percentage of live weight significantly improved when nitrate levels increased (P<0.000). Goats fed urea alone and urea+ 2% nitrate consumed as much as 2.9% feed of its body weight with the subsequent increase of 3% for urea plus 4% nitrate and 3.1% when nitrate as sole fermentable nitrogen supplement (table 4). Mean values of goat performance was shown in table 4.

^abc Mean values within rows without common superscript are different at P< 0.05

KN0: Goats supplemented with urea equivalent to 6% nitrate based on dry matter intake (DMI)

KN2: Goats supplemented with 2% nitrate and urea equivalent to 6% nitrate based on DMI

KN4: Goats supplemented with 4% nitrate and urea equivalent to 6% nitrate based on DMI

KN6: Goats supplemented with 6% nitrate based on DMI

The growth curves (figure 1) implied significant and gradual increase in live weight gain among all diets although there were some fluctuations within the first 21 days of experiment due to the problems of animals adapting to a new ration.

Effect of supplementary nitrate on gas profile

Nitrate-N diet decreased ratio of methane to carbon dioxide (P<0.000).  The result (figure 2) showed the largest drop when nitrate (6% of dry matter of feed) provided the sole supplementary nitrogen. Difference was almost incredible, but tendency of the fall was clear that there was a very gradual reduction of methane and carbon dioxide when nitrate toke the place of urea as a nitrogen supplement. With 6% potassium nitrate, CH4:CO2 ratio was 0.0057 which was very close to atmospheric ratio 0.0047. Thus, inhibitory effect of nitrate on methanogen was very strong.

Discussion

Feed intake increased in every added level of nitrate and animals appeared to be healthy for the whole period of experiment with 6% nitrate in diet dry matter. The result partly disagreed with Farra & Satter (1970) and Arora (1968) who reported that feed intake was reduced when nitrate exceeded 4% of diet dry matter and methamoglobinemia appeared at higher nitrate although Nolan (2010) claimed that sheep were safe with insignificant difference of dry matter intake when 4% nitrate were supplemented. Adaptation and method of feeding were important when nitrate was added in the diet because it could suppress dry matter intake due to its low palatability.

The grow curve was linear although there was no statistical difference of live weight gain between urea-diet and nitrate-diet and this result agreed with Hao (2009) and Ngoc (2010). There were two possible reasons for the insignificant growth performance among all rations. Firstly, it may be attributed to the equal intake of fixed amount of mimosa foliage and water spinach in the basal diet which accounted for a large percentage of nitrogen supply for all animals although rice straw was the single factor to drive up total dry matter intake as percentage of body weight which at last did not bring much change to animal performance. Then, conversion of nitrate and urea to microbial nitrogen synthesis was insignificant. This has been previously reported that microbial crude protein outflow was not significantly different between nitrate and urea supplementation, but advantage of nitrate-N diet over urea-N diet in microbial synthesis made nitrate containing ration slightly better (Nolan 2010; Guo 2009).

The effect of nitrate on methane production was just phenomenal. Reduction of methane production was very precise when nitrate was used as a sole supplementary nitrate. The reduction of methane went above 100%, but it was relatively high compared with previous reports. Bozic (2009) reported that methane production dropped by 98% after third-24 h incubation series with tested sodium nitrate although Nolan (2010) failed to have a big response when he supplemented sheep with 4% nitrate and reduction of methane production was just 23%.

The high reduction of methane might be attributed to a number of factors. Possibly, gas sample was taken at the end of 84-day experiment which was probably long enough for nitrate to almost completely repress methanogenic bacteria and that agreed with previous report using Scanning Electron Microscope by Jeong (2005). In addition, low CH₄:CO₂ ratio could be a consequence of sampling method by breathed air which needed to be done more to get a standard and accuracy of sampling technique. Hindrichsen (2005) reported that 85-90% of methane was produced by enteric fermentation and Murray (1976) indicated that 95% of those produced by enteric fermentation was excreted by eructation, whereas 89% of methane was excreted by breathed air and 11% by anus for those which was produced by hindgut.

Nitrate effectively inhibits methane production and that was also reported previously by Nolan 2010, Jeong 2005, Bozic 2010, Detlef 1998, Guo 2009, Guangming 2010, and Mohanakrishnan 2008.

Conclusion

• High level of nitrate supplementation is safe for well adapted ruminants

• Nitrate supplementation on diet high in rumen bypass protein is effective

• Increase of feed intake can be achieved unless method of feeding is well considered and nitrate should be used to replace urea as a fermentable nitrogen supplement without affecting animal growth performance

• Nitrate can almost totally inhibit methane gas emission from ruminants  

Acknowledgements

The senior author would like to express his grateful thank and gratitude to SIDA-SAREC and the MEKARN program for financial support. He would like to thank for students and staffs of department of animal science in Kampong Cham National School of agriculture for help and laboratory use.

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