Effect of calcium nitrate as NPN source on growth performance and methane emissions of goats fed sugar cane supplemented with cassava foliage

Nguyen Ngoc Anh, Khuc Thi Hue, Duong Nguyen Khang* and T R Preston**

Goat and Rabbit Research Center, Son Tay, Hatay, Vietnam
anhnguyenngoc9@g,mail.com
*Nong Lam University, Thu Duc, Vietnam
**TOSOLY, AA 48 Socorro,  Colombia

Abstract

The hypotheses that were tested in this experiment were:   calcium nitrate will support the same growth rate as urea when used as the source of rumen-fermentable N in diets based on sugar cane for growing goats; methane concentrations in the rumen gas of goats will be reduced when calcium nitrate is the N source compared with urea. The experiment was with 32 growing goats of 10 kg initial live weight and continued for 84 days at the end of which the ratio of methane  to carbon dioxide. in expired air was determined using a “GASMET” analyser. Feeding was chopped sugar cane ad libitum and fresh cassava foliage at the rate of 1.5% of LW (DM basis). The treatments were: calcium nitrate or urea as the source of NPN. Sodium sulphate was added to both diets to give 0.4% of S in the diet. The urea/calcium nitrate was dissolved in water and sprinkled over the sugar cane. The sodium sulphate was given in the same solution. The levels of the NPN sources were fixed at 1.2% N in the diet DM equivalent to 5.0% calcium nitrate and 2.6% urea.

Key words

Introduction

Livestock contribute some 30% of greenhouse gases according to FAO (2007). The production of methane from rumen fermentation is the main source of these emissions. There is thus an urgent need to develop ways of reducing methane emissions from ruminants. From a survey of the relevant literature, Leng (2008) concluded that the presence of nitrate salts in the rumen will act as a sink for the hydrogen produced by fermentation of carbohydrate such that it is converted to ammonia rather than methane. Results of recent research with sheep in Australia and The Netherlands (Nolan et al 2009; Van ---- 2010) indicate that the proportion of methane in the rumen gas of can be reduced substantially by feeding sodium nitrate instead of urea as the source of non-protein nitrogen.  Trinh Phuc Hao et al. (2009) showed that potassium nitrate could be safely fed as the sole source of fermentable N provided the animals (goats) were adapted to the diet over a period of 2 weeks. N retention was the same with potassium nitrate as with urea as the source of fermentable N. Guo et al (2009) showed that methane:carbon dioxide ratios were reduced in an in vitro incubation in which sodium nitrate replaced urea as the sole source of N, with starch  and cellulose as carbohydrate sources. Similar findings have been reported by Le Thi Ngoc Huyen et al (2010) using sodium nitrate compared with urea in an in vitro incubation using NaOH-rice straw as the carbohydrate substrate. According to Leng (2008), the dietary conditions which favour utilization of nitrate to lower the production of methane are: a source of easily fermentable carbohydrate, a low content of soluble protein, adequate level of sulphur and a source of bypass protein.

Sugar cane satisfies the need for a basal diet that is rapidly fermentable (contains 50% sugar in the DM) and is low in soluble protein (less than 1% in DM). It has been shown to support growth rates in cattle of over 700 g/day when supplemented with urea and rice polishing as a source of bypass nutrients (Preston et al 1976). It is widely grown by farmers in the Bavi area.

Objectives

To study the effect of urea and calcium nitrate on rumen methane levels, growth and feed conversion in growing goats fed basal diets of sugarcane supplemented with cassava foliage.

Materials and methods

Location and climate of the study area

The experiment was conducted in the Goat and Rabbit Research Center of NIAS, situated in Bavi, Hanoi. The climate in this area is tropical monsoon with a summer season between April and November and a winter season from December to March. Average annual rainfall is 1850 mm. The trial was conducted during April to August, 2009.

Treatments and design

A completely randomized design was used to compare two treatments:

•  Urea-SC: Sugarcane + Urea + Cassava foliage
•   Ca-SC: Sugarcane + Calcium nitrate + Cassava foliage

Animals

Sixteen goats (Saanen and Alpine breeds) with initial live weights of 12 -13 kg, with equal numbers of males and females,  were used. They were confined in separate cages giving 8 replicates of each treatment. They were treated with Ivermectin to control internal and external parasites before starting the experiment.

Feeds and feeding

Sugarcane grown in the Centre was chopped by hand to particle size of of 3-5mm before feeding ad libitum to the goats. The fermentable N sources were Urea and Calcium nitrate which were purchased. Sodium sulphate was added to give 0.4% of S in the diet. The source of bypass protein was fresh cassava foliage fed at the rate of 1.5% of live weight (on DM basis). It was grown at the Center. The urea/calcium nitrate was dissolved in water (100 g of each in 200ml of water) and sprinkled over the sugar cane. The sodium sulphate was given in the same solution. The first offer of sugarcane was at 07.00 and the second at 3.00 pm. The levels of the N sources were fixed at 1.2% N in the diet DM equivalent to 5.0% calcium nitrate and 2.6% urea. Prior to starting the experiment the goats were adapted gradually over a 14 day period to increasing proportions of nitrate/urea in the diet as in Table 1.

The feeding schedule is shown in Table 2.

Measurements

Feeds offered and refused were recorded daily and samples taken at 14 day intervals for determination of DM and N. The animals were weighed at the beginning and then every 14 days over the experimental period of 140 days. Samples of rumen fluid were taken by stomach tube after 50 days for determination of ammonia. At the end of the experiment, eructed gases from every animal were sampled for determination of concentrations of methane and carbon dioxide according to a modification of the procedure proposed by Madsen et al (2010). The eructed gases were merged with background air by enclosing the goats in a closed box (Photo 1) for a period of 5 minutes, prior to measuring the content of methane and carbon dioxide with a Gasmet meter (Gasmet Technologies Oy, Pulttitie 8A, FI-00880 Helsinki, Finland). The concentrations of methane and carbon dioxide in the backgrond air were also measured.  The ratios of methane to carbon dioxide were calculated as:

CH₄: CO₂ = (a-b)/(c-d)

Where "a" is methane concentration in mixed eructed gas plus air, "c" is carbon dioxide concentration in mixed eructed gas plus air, "b" is methane in background air and "d" the carbon dioxide in background air. As feed intake and composition did not differ among treatments it was assumed that carbon dioxide production was also similar and could be used as internal marker as described by Madsen et al (2010).

Chemical analyses

The DM and Ncontent of the feeds and resxidues,  and ammonia in rumen fluid, were analysed according to AOAC (1990). The sugar content of the sugar cane was  determined daily by analyzing the juice with a hand refract meter.

Statistical analyses

The data were analyzed using the general linear model of the ANOVA program in the Minitab software (version 15.51). In the model the sources of variation were nitrogen source and error. Weight gains were measured by the linear regression of live weight (Y) on days in the experiment (X).

Results and discussion

The chemical composition of the experimental feeds is shown in Table 1. The low sugar content of the sugar cane indicates that it was relatively immature at the time of harvest. 

Feed intake and nutrient intake

The goats were fed safely the calcium nitrate as NPN source and were adapted well to the feeds over the whole experimental period. This result is the sane as was reported by Trinh Phuc Hao et al. (2009). 

Live weight gain and feed conversion ratio

Daily live weight gain and DM feed conversion did not differ between the treatments. Growth was uniform for both treatments throughout the experiment (Figure 1)..

Gas production

Table 4. Gas production of goats fed with urea or nitrate supplements as N-source

While the ammonium content in rumen liquor and carbon dioxide production did not show significant differences between treatments (Table 4), the methane production was clearly higher (154 ppm) in the urea treatment than in the nitrate treatment (104 ppm). This had consequently also an effect on the CH₄/CO₂ ratio, which was higher with urea. Leng (2008) concluded that the presence of nitrate salts in the rumen will act as a sink for the hydrogen produced by fermentation of carbohydrate such that it is converted to ammonia rather than methane.

References

AOAC 1990 Official methods of analysis (15th edition), Washington DC

Guo W S, Schaefer D M, Guo X X, Ren L P and Meng Q X 2009 Use of nitrate-nitrogen as a sole dietary nitrogen source to inhibit ruminant methanogenesis and improve microbial nitrogen synthesis In vitro, Asian-Aust.J.Anim.Sci. Vol.22, No.4: 542-594, April 2009.

Le Thi Ngoc Huyen, Ho Quang Do, Preston T R and Leng R A 2010 Nitrate as fermentable nitrogen supplement to inhibit methane production in cattle. Livestock Research for Rural Development. In preparation

Leng R A 2008 The potential of feeding nitrate to reduce enteric methane production in ruminants. A Report to The Departmernt of Climate Change Commonwealth Government of Australia. ACT Canberra Australia For paper and PPT presentation see http://www.penambulbooks.com/Downloads/Leng-Final%20Modified%20%2017-9-2008.pdf