Effect of biochar on growth and methane emissions of goats fed fresh cassava foliage

Le Thi Thuy Hang, T R Preston¹, Nguyen Xuan Ba² and Dinh Van Dung²

Faculty of Animal Sciences and Veterinary Medicine, Agricultural and Natural Resources Faculty, An Giang University, Vietnam
thuyhang.agu@gmail.com
¹ Centro para la Investigación en Sistemas Sostenibles de Producción Agropecuaria (CIPAV), Carrera 25 No 6-62 Cali, Colombia
² Hue University of Agriculture and Forestry, Hue University, Hue City, Vietnam

Abstract

Twelve growing male goats of the Bach Thao breed, with an initial body weight from 14 to 16 kg, were housed in individual cages and given a basal diet of ad libitum fresh cassava foliage (sweet variety) supplemented with 4% (DM basis) of ensiled brewers’ grain. The length of the trial was 12 weeks after a period of 10 days to accustom the goats to the diets. The hypothesis underlying the research was that there would be a dose response in growth rate to biochar over the range of 0 to 1.5.% in diet DM.

For all the growth criteria (feed intake, live weight gain and feed conversion), expected to be influenced by nutrient manipulation of ruminant diets the responses were curvilinear with positive effects from increasing biochar supplementation from 0 to 0.8% of the diet DM followed by a decline as the biochar level was raised to 1.3% in diet DM. By contrast, in terms of effects on the rumen fermentation the improvement (decrease in methane production) was linear.

It is hypothesized that the beneficial effects of biochar on growth of goats and cattle fed cassava products is because the biochar provides habitat for microbial communities that reduce the toxic effects of the HCN while still retaining its beneficial effects in modifying the sites of digestion with positive effects on growth and feed conversion.

Key word: brewers’ grain, feed conversion, forages, greenhouse gas

Introduction

The population of goats in An Giang in 2017 was 6 times higher than in 2012 (Statistic yearbook of An Giang 2017). The relative price of meat from goats is higher than that from other species of livestock, eg: price of goat (for meat) 3.2 USD/kg LW compared to cattle (2.5 USD/kg LW) (Do Thi Thanh Van et al 2018). Most goats are kept in confinement in small scale systems with the feed supplied from around the household or close by (eg: natural grasses, water spinach, sweet potato leaves…but not cassava foliage, that is traditionally thrown away, or burned, causing environment pollution.!! ). This contrasts with the reports of Wanapat et al (1997) and Preston (2001) that cassava foliage can be a valuable source of protein for feeding to many kinds of animals.

Brewers’ grains are the solid residue left after the distillation of germinated cereal grains to produce beer and other alcoholic beverages. The recent reports of benefits in growth and health of cattle and goats fed small quantities of brewers’ grains (Thuy Hang et al 2018; Silivong et al 2018; Binh et al 2017). are believed to be related to their “prebiotic” qualities in enhancing the action of beneficial microbial communities along the digestive tract of the animal (Inthapanya et al 2019).

Biochar is generated from the partial combustion of fibrous biomass, and although primarily used as a soil amendment (Lehmann and Joseph 2009; Preston 2015), it has recently been reported that at a level of 1% of the diet DM, it enhanced the growth rate and reduced enteric methane emissions of cattle (Leng et al 2012) and goats (Binh et al 2018; Silivong et al 2016).

The hypothesis underlying the research reported in this paper was that growth rate and methane emissions of goats would reflect a dose response relationship to biochar, which merited the study of levels of biochar in the range of 0 to 1.5.% in diet DM.

Materials and methods

Location and duration

The experiment was carried out in the farm of the Faculty of Agricultural and Natural Resources, An Giang University, An Giang Province, Vietnam, from February 2018 to May 2018.

Experimental design

Twelve growing male goats of the Bach Thao breed, with an initial body weight from 14 to 16 kg, and about 3.5 – 4.5 months of age, were housed in individual cages (Photo1) and given a basal diet of fresh cassava foliage ad libitum plus 4% (DM basis) of ensiled brewers’ grain. Treatments were 4 levels of biochar: 0, 0.5, 1.0 and .1.5% of diet DM. The design was a random block with three replicates of the four treatments. The trial was for 12 weeks after a period of 15 days to accustom the goats to the diets.

Photo 1. The elevated cages for the goats

Feeding and management

The cassava foliage was from a “sweet” variety planted in the University area. It was harvested after periods of re-growth of 2-3 months and fed 2-3h after harvesting. During rainy days, the foliage was harvested the day before feeding to limit the effects of excessive moisture on the foliage DM content. Harvesting was by hand-cutting the cassava stems at ground level then rejecting the lower 30cm of “hard” stem (Photo 2). The foliage was presented to the goats by hanging it in bunches in front of the feed troughs.

Photo 2. The “hard” stem 30-40cm from the ground (red line on the left) was rejected. The rest of the plant (red line on the right) was suspended in the pens for the goats to choose freely

The brewers’ grains were brought from the brewery in Kien Giang Province every 10 days. They were stored in closed plastic bags in a naturally ensiled state (pH = 4.28 ± 0.46). The chosen amounts were offered twice daily in troughs. The biochar was produced by burning rice husks in a top-lit, updraft (TLUD) gasifier stove (Olivier 2010).To reduce the “dusty” nature of the biochar it was mixed with a small amount of water enough to moisten the biochar but avoiding any excess. The chosen amounts were offered twice daily in troughs separate from the brewers’ grain (Photo 3). Drinking water was freely available.

Photo 3. Separate troughs for the brewers’ grains and the biochar

Before starting the experiment, the goats were treated against parasites with injections of Ivermectin solution (1 ml per 4 kg LW) and vaccinated against pasteurellosis, enterotoxaemia, foot and mouth disease and goat pox. They were adapted to the experimental feeds for 15 days before starting the collection of data. Cassava foliage was offered at 7:30 and 14:30, while the brewers’ grains and biochar were given at 9:30 and 16:30. Mineral lick blocks (460 g limestone meal, 220 g bone meal, 50 g sulphur, 100 g salt plus 170 g cement as a binding agent) were available ad libitum by hanging on the walls of the pens. Feeds offered and refused were recorded daily.

Measurements

Live weight was recorded in the morning before feeding at the beginning and at 10-day intervals until the end of the 90-day experiment. Live weight gain was calculated from the linear regression of live weight (Y) on days from the start of the experiment (X).

Feed consumption was recorded by weighing feeds offered and refusals from individual animals every morning before offering new feed. Cassava foliage (offered and residues) was separated into stems and leaves (containing attached petioles) (Photo 4). Representative samples of each component were stored at -18°C until they were analyzed.

Photo 4. Collecting samples of residues of the cassava foliage

Eructed gas emissions and analysis

At the end of the experiment the goats were confined individually in a closed chamber (a bamboo frame covered with polyethylene plastic) for sampling of eructed gases and residual air in the chamber (Madsen et al 2010). Measurements of the concentrations of methane and carbon dioxide were taken continuously over a 10-minute period, using a Gasmet infra-red meter (GASMET 4030; Gasmet Technologies Oy, Pulttitie 8A, FI-00880 Helsinki, Finland).

Analytical procedures

Samples of feeds offered and refused were analysed for DM, crude protein (CP) and ash by AOAC (1990) methods. Neutral detergent fiber (NDF) and acid detergent fiber (ADF) were determined by the methods of Van Soest et al (1991). The equivalent hydrogen cyanic acid content (HCN) in leaves-petioles of fresh cassava leaves was determined as per AOAC  (2016). Condensed tannins were determined by the method of AOAC 955.35 (2016)

Statistical analysis

Data were analyzed with the General Linear Model option of the ANOVA program in the MINITAB software (Minitab 2000). Sources of variation were treatments and error. Production responses (feed intake, live weight gain and feed conversion) were related to percent biochar in the diet using polynomial regression equations from Microsoft Office Excel software.

Results

Composition of diet ingredients

The levels of crude protein in the cassava leaves and combined leaf-petioles (Table 1) were similar to those reported by Sina et al (2017). The “equivalent HCN” values in the leaf-petioles (115 mg/kg DM) were much less than the 500 mg/kg DM reported by Phuong et al (2019) for leaf-petioles in sweet cassava.

Two batches of biochar were used in the experiment. The first batch, which was fed during the 15-day adaptation period and the first 10 days of the growth trial, had a water retention capacity of 3.81 ml water/g dry biochar. The second batch which was fed from day 10 of the feeding trial to the end (90 days) had a much higher water retention capacity of 4.89.

Feed intake, growth and feed conversion

For all the growth criteria expected to be influenced by nutrient manipulation of the diets the responses were curvilinear with positive effects from increasing biochar supplementation from 0 to 0.8% of the diet DM followed by a decline as the biochar level was raised to 1.3% in diet DM (Table 2; Figures 1-3). By contrast, in terms of effects on the rumen fermentation the improvement (decrease in methane production) was linear (Table 4; Figure 4).

Figure 1. Curvilinear response of DM intake of goats to percent biochar in a cassava foliage diet with the optimum level at about 0.8 % biochar in DM	Figure 2. Curvilinear response of live weight gain of goats to percent biochar in a cassava foliage diet with the optimum level at about 0.8 % biochar in DM

Figure 3. Curvilinear response in DM feed conversion of goats according to percent biochar in a cassava foliage diet with the optimum level at about 0.8 % biochar in DM	Figure 4. Linear reduction in methane:carbon dioxide ratio in eructed gas of goats fed up to 1.3% biochar in a diet of cassava foliage

Discussion

Biochar quality

It has been shown that the growth of a biochar test plant (maize) was linearly related to the water retention capacity of the biochar used as soil amendment (Nguyen Van Lanh et al 2019). The fact that growth rates increased when the 4.89 WHC bochar was fed, as compared with the previous period with 3.81 WRC biochar (Figure 5) is an interesting unsubstantiated observation that merits further research relating to the water retention capacity of biochar and its relative value as an additive in livestock diets.

Figure 5. Growth response curves to biochar with water retention capacities of 3.81 and 4.89 fed in succeeding periods (-15 to + 10 days) and 10-90 days)

Growth and feed conversion

The 26% increase in growth rate from including 0.8% biochar in the diet of goats in the present experiment concurs with growth responses observed in: (i) goats fed legume tree and cassava foliage (Silivong et al 2016) or foliages from sweet and bitter cassava varieties (Phuong et al 2019); and (ii) in cattle fed cassava roots and cassava foliage (Leng et al 2012; Sengsouly and Preston 2016; Saroeun et al 2018). Common to all these reports is the presence of cassava foliage and cassava roots as major components of the diet.

Both roots and foliage of cassava contain cyanogenic glucosides that give rise to toxic HCN when exposed to enzymes in the digestive tract of animals and humans. We hypothesize that the beneficial effects of biochar on growth of goats and cattle fed cassava products is because the biochar provides habitat for microbial communities that reduce the toxic effects of the HCN while still retaining its beneficial effects in modifying the sites of digestion as discussed by Inthapanya et al (2019).

Conclusions

• Feed intake, live weight gain and feed conversion were improved by increasing biochar supplementation from 0 to 0.8% of the diet DM followed by a decline as the biochar level was raised to 1.3% in diet DM.
  
  
•  Rumen methane emissions were reduced with a linear trend as the level of biochar in the diet was increased.
  
  
• It is hypothesized that the beneficial effects of biochar on growth of goats and cattle fed cassava products is because the biochar provides habitat for microbial communities that reduce the toxic effects of the HCN while still retaining its beneficial effects in modifying the sites of digestion with positive effects on growth and feed conversion and in reduction of enteric methane.

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Received 6 March 2019; Accepted 4 April 2019; Published 1 May 2019

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