Livestock Research for Rural Development 31 (8) 2019 Guide for preparation of papers LRRD Newsletter

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Growth rate of Holstein-Friesian cattle was increased, and eructed methane was reduced, when a basal diet of cassava pulp-urea was supplemented with cassava foliage and coconut cake

Duong Nguyen Khang, Dang Thi Ngoc Anh and T R Preston1

Nong Lam University of Ho Chi Minh City, Vietnam
1 Centro para la Investigación en Sistemas Sostenibles de Producción Agropecuaria (CIPAV), Carrera 25 No 6-62 Cali, Colombia


This objective of this study was to evaluate the effects of supplements of coconut cake and cassava foliage on growth performance and methane emissions in Holstein-Friesian cattle fed a basal diet of cassava pulp and urea. The supplements were fed separately at 30% of diet DM or together each at 15% of diet DM.

Growth rate was increased, feed conversion ratio was improved, and eructed methane decreased when the basal diet of cassava pulp-urea was supplemented with either cassava foliage or coconut cake fed separately or together. Offering equal quantities of cassava foliage and coconut cake supported better growth and feed conversion, with less methane production, than when these supplements were given separately at the same overall levels of crude protein.

Key words: bypass protein, feed conversion, HCN precursors


Enteric methane from ruminants is estimated to represent 17–30% of total anthropogenic methane (Beauchemin et al 2007). The methane production resulting from methanogenesis also represents a loss of dietary energy to the animal, from 2 to 12% of the gross energy intake (Johnson and Johnson 1995). These factors have led to a global search for nutritional strategies to mitigate methane emission from ruminants.

The increase in dairy production in Vietnam is mainly taking place through the establishment of medium to large scale dairy farms using Holstein cattle. In this system the male calves are wasted as they are considered unsuitable for beef production, due to their poor conformation and low capacity to lay down fat in the muscles, which is an essential feature in order to produce meat of “good quality”.

This problem was solved in European countries where intensive fattening of Holstein male calves was developed originally in Scotland by feeding a diet exclusively of barley grain and soybean meal after 3-5 week early weaning (Preston and Willis 1974). This system because of its high nutrient status supported growth rates of over 1 kg/day and the early deposition of fat resulting in beef that was tender and of attractive flavor (Preston and Willis 1974).

Feeding cereal grain to cattle in the SE Asia area is neither politically nor socially desirable nor economically feasible. However, there are byproducts which could substitute for the cereal grains and which presently are often major sources of pollution. Cassava pulp, a presently under-utilized and often polluting byproduct from starch manufacture from cassava, is such as example.

The use of ensiled cassava pulp (sometimes named cassava pomace) as the basis of the feeding system for ruminant animals is a relatively new development. Interest in the feasibility of using this by-product was stimulated by the finding in the cassava starch factory in Vientiane province, Lao PDR, that the pulp that had been “dumped” in an open pit (the pit measured 200*50m by 8m depth = about 80,000 t) over a 4-year period had ensiled naturally (pH<3.5) and had a potential feed value only slightly less than in the entire cassava root (Phanthavong et al 2014). The potentially high feeding value of the ensiled pulp was confirmed in subsequent feeding trials (Phanthavong et al 2016, 2017, 2018) in which young cattle of the local “Yellow” breed were fed ad libitum on the ensiled pulp with added urea, supplemented with ensiled brewers’ grains and rice straw. The growth rates on this feeding system were 700-900 g/day with a DM feed conversion less than 7.00.

Fresh brewers’ grains are known to be an excellent source of bypass (escape) protein (Promkot and Wanapat 2003) but their availability is restricted to areas close to the breweries. Cassava foliage which has been used successfully as a protein supplement for cattle (Ffoulkes and Preston 1978), goats (Ho Quang Do 2002) and sheep (Khuc Thi Hue 2012), is widely available as a co-product of cassava root production and is proposed as the most promising protein supplement to accompany the cassava pulp-urea basal diet.

Coconut cake from traditional coconut processing was recommended for methane abatement in the in vitro study of Soliva et al (2007). Coconut cake is the byproduct from the extraction of coconut oil, representing from 34 to 42% of the weight of the nut, containing from 18 to 25 % crude protein in DM. When the mechanical expeller process is used to extract the oil, the protein-rich byproduct is likely to be a good source of “bypass” protein, as the combination of the heat produced in processing, and the presence of residual oil, will tend to protect the protein against degradation in the rumen, thus conferring rumen “bypass” or “escape” properties to the protein (Preston and Leng 1987).

The aim of the experiment described in this paper was to evaluate the use of cassava foliage and coconut cake as sources of bypass protein to balance the basal diet of cassava pulp-urea for the fattening of Holstein cattle.

Materials and methods


The experiment was conducted in the cattle farm of the Research and Technology Transfer Center of Nong Lam University from April to December 2016.

Treatments and experimental design

Sixteen Holstein-Friesian heifers of 143-156 kg live weight were housed in individual pens (Photo 1) and blocked in 4 groups according to live weight. Within groups they were allocated to one of the four diets described in Table 1, according to a completely randomized block design. Urea was mixed with the cassava pulp at levels equivalent to 2.5% of the pulp DM; sulphur-rich minerals (2% of diet DM) were supplied for all treatments.

Table 1. Ingredients and chemical compositions of diets in the experiment

Diets (% in DM)





Ingredients, %

Cassava pulp





Cassava foliage





Coconut cake










Calculated composition, % in DM

Crude protein





Vaccination was done against epidemic diseases and the cattle were drenched against internal parasites before beginning the experiment.

Photo 1. The HF heifers housed in individual pens
Feeding and management

A mineral mixture (25% salt, 25% calcium carbonate, 45% calcium di-phosphate, and 5% sulphur), and water were freely available on all treatments. The fresh cassava foliage (sweet variety) was harvested daily from the plots already established in Nong Lam University. The cassava pulp was collected from the Wuson cassava factory in Binh Phuoc province. Coconut cake was purchased from a coconut milk factory in Ben Tre province.

Fresh feed was offered at 7.30 am and 3.30 pm. The cattle were adapted gradually to the experimental feeds for two weeks prior to starting the experiment.

Data collection and measurements

The cattle were weighed at the beginning and every 30 days, using an electronic balance. Feeds offered were weighed before giving them to the cattle. Feed refusals were collected each morning prior to offering fresh feed and weighed to measure the feed intake. Samples of feeds offered and refused were collected every 14 days for analysis. At the end of the experiment, a sample of mixed eructed and respired gas from each animal was analyzed for methane and carbon dioxide using the Gasmet equipment (GASMET 4030; Gasmet Technologies Oy, Pulttitie 8A, FI-00880 Helsinki, Finland), based on the approach suggested by Madsen et al (2008). The cattle were held for one whole day in a closed chamber before taking measurements, at one minute intervals over 10 minutes, of the concentrations of methane and carbon dioxide in the mixed air and eructed gas (Photo 4). Samples of air in the animal house were also analyzed for the methane:carbon dioxide ratio.

Photo 2. The HF cattle housed in individual cage before weighing
and measuring enteric methane production
Photo 3. Closed chamber used to measure
enteric methane production
Chemical analysis

Samples of feeds offered and residues were analyzed for DM and crude protein (CP) following AOAC (1990) procedures. Protein solubility (Whitelaw and Preston 1963) was measured by weighing 3 g of sample (DM basis), followed by shaking in 100 ml of M NaCl for 3 h. The suspension was then filtered through Whatman No. 4 filter paper and washed 3 times with distilled water. All the filtrate was then transferred to a kjeldahl flask for digestion, distillation and titration according to AOAC (1990). Protein solubility was calculated as the N content of the filtrate as a percentage of the N in the original sample.

Statistical analysis

Data for feed intake, live weight gain, feed conversion and ratio of methane to carbon dioxide in mixed eructed gas and air, were analysed by the General Linear Option in the ANOVA program of the Minitab Software (Minitab 2016). Sources of variation were protein supplements and error. Response curves were fitted to the data using linear and quadratic equations in the Microsoft Office Excel software, with live weight gain and feed conversion as the dependent variables (Y) and feed intake, methane: carbon dioxide ratio as independent variables (X).


Feed intake, live weight gain and feed conversion

The predominant role of cassava pulp is evident in all the diets (Figure 1). There were major differences in the solubility of the protein between coconut cake and cassava foliage, with the protein in coconut cake being less soluble than the protein in cassava foliage (Table 2).

Table 2. Proximate analysis of dietary ingredients


% in DM

of CP, %,





Cassava pulp







Cassava foliage







Coconut cake







The growth rate on the CP-U diet of 513 g/d was surprisingly high (Table 3) considering that the true protein content of the diet was only 3.5% in DM with crude protein as urea supplying 70% of the dietary nitrogen. This growth rate is much superior to that reported on a low protein diet of molasses-urea when growth rates were only slightly above maintenance for similar levels of urea (Preston and Willis 1974). Such a difference is in accordance with reported patterns of rumen VFA with molar propionate being much higher on starch-based feeds such as those from cassava roots as compared with sugar-based molasses (Preston and Leng 1987).

Figure 1. Proportions (DM basis) of major ingredients in the diets

Table 3. Mean values for changes in live weight, DM intake, feed conversion, ratio of
methane: carbon dioxide in eructed gas and crude and insoluble protein in diet DM








Live weight, kg















Daily gain







DM intake, kg/d







Feed conversion







Crude protein

% in diet DM





% insoluble#





CH4:CO2 ratio







# Proportion of total crude protein not solubilized by extraction with M NaCl

The relationship between live weight gain and feed intake was curvilinear (Figure 2) with an increasing response to feed intake when the protein supplement was derived from both protein sources. The superior response in live weight gain to coconut meal compared to cassava foliage, when each supplied equal quantities of protein was in contrast to the result when the two sources were combined, when the growth response was greater than when either protein supplement was fed separately (Table 3; Figure 3).

Figure 2. Curvilinear relationship showing increasing response to feed intake when the protein
supplements were combined as compared with being fed separately

Figure 3. Live weight gain was increased when equal proportions of the two
supplements were fed compared with them being fed separately
Methane production

The close relationships between between methane production and live weight gain and feed conversion (Figures 3 and 4) show that the ratio of methane: carbon dioxide in mixed eructed gas and air is a good indicator of the balance of nutrients arriving at sites of metabolism and hence of potential animal productivity. Similar relationships were observed by other researchers (Phonethep et al 2017; Phanthavong et al 2017; Sangkhom et al 2017; Hamdani et al 2019) in experiments where supplementation was manipulated to promote reduced rumen methane production.

Figure 4. Relationship between live weight gain and ratio of methane to carbon dioxide in mixed air and eructed
gas from cattle fed cassava foliage and coconut cake as supplements to cassava pulp-urea

Figure 5. Relationship between feed conversion and ratio of methane to carbon dioxide in mixed air and eructed
gas from cattle fed cassava foliage and coconut cake as supplements to cassava pulp-urea


The improvement in growth rate and feed conversion when the bypass protein source was a mixture of cassava foliage and coconut meal implies that the cassava foliage provided elements other than bypass protein, the supply of which was lower when cassava foliage rather than coconut meal was the major protein source. The presence of HCN precursors in cassava leaves , acting to depress rumen fermentation and facilitate nutrient escape to posterior sections of the digestive tract leading to more efficient utilization of protein (in the small intestine) and carbohydrate (in the cecum), was suggested by Binh et al (2018) in studies with goats and by Duong Nguyen Khang et al (2018) based on rumen in vitro studies with the same ingredients as used in the present experiment.



The authors acknowledge support from the MEKARN II project financed by Sida. We thank the Research and Technology Transfer Center, Nong Lam University, Vietnam for providing infrastructure support.


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Received 12 June 2019; Accepted 2 July 2019; Published 1 August 2019

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