Effect on feed intake, digestibility, N retention and methane emissions in goats of supplementing foliages of cassava (Manihot esculenta Crantz) and Tithonia diversifolia with water spinach (Ipomoea aquatica)

Phonethep Porsavatdy, T R Preston¹ and R A Leng²

Animal Science Department, Faculty of Agriculture and Environment, Savannakhet University, Lao PDR
pphonetheb@gmail.com
¹ Centro para la Investigación en Sistemas Sostenibles de Producción Agropecuaria (CIPAV), Carrera 25 No 6-62 Cali, Colombia
² University of New England, Armidale, NSW, Australia

Abstract

Four growing male goats (Bach Thao breed) with body weight in the range from 10 to 13.5 kg and about 4-6 months of age were fed basal diets of sweet cassava foliage or Tithonia diversifolia without or with supplementation with fresh water spinach.

Appparent DM digestibility was higher by 30% for diets based on Tithonia than on cassava foliage and was improved slightly (about 3%) when water spinach was also fed. There was a 21% increase in N retention when cassava was the main foliage rather than Tithonia, but the apparent benefits from giving water spinach were less (about 8%). Methane emissions in eructed gas were reduced by 50% when cassava rather than Tithonia was the main foliage in the diet, and were increased when water spinach was also fed. It is postulated that on such feeds the balance of feed fermented in the cecum/large intestine relative to the rumen is increased. As  disposal of hydrogen in fermentation degradation in the cecum-colon appears to be dominated by acetogenesis, this would account for decreased methane production on such diets.

Key words: acetogenesis, bypass protein, cecum, escape protein, HCN, soluble protein, tannins

Introduction

A major priority in contempory livestock research is to develop feeding systems which result in reduced emissions of methane, both from eructed gas of ruminants and from decomposition of livestock excreta. Feeds which are highly digestible produce less feces, and therefore there is reduced potential for methane production from this source. Diets of high nutrient density generally support higher levels of production than diets of low nutrient density, and hence there is less methane produced per unit output of meat or milk. However,  diet digestibility per se does not appear to be a guide to potential enteric methane production in ruminants; it is proposed that it is the proportion of the digestible feed that escapes the rumen that appears to be one of the determining factors. 

The concept that ruminant productivity on highly digestible diets is mainly determined by the rumen escape (or bypass) properties of protein, as proposed by Preston and Leng (1987), was based on the findings of Whitelaw and Preston (1963) that the solubility of the protein, rather than the amino acid profile, was the major determinant of N  retention in weaned calves fed a nutrient-rich diet (mainly flaked maize and either rumen insoluble or soluble fish meal or groundnut meals).  This concept was subsequently linked to effects of protein solubility on methane produced in in vitro rumen incubations.  Thus Preston et al (2013) reported that  methane produced per unit substrate mineralized in an in vitro rumen fermentation was less when fish meal (protein solubility 17%) rather than groundnut (Arachis hypogaea) meal  (protein solubility 76%) was the protein supplement.  Similarly in an in vitro rumen fermentation of forages of varying protein solubility, methane per unit substrate DM mineralized was 33% higher in forages containing highly soluble protein (water spinach and sweet potato (Ipomoea batata) vines; protein solubility of  71%) compared with those of low protein solubility (Sesbana grandiflora and cassava leaves; protein solubility 34 and 35%) (Do et al 2013).

The hypothesis that protein solubility is an indicator of potential methane production in ruminant animals is further developed in the research reported in this paper, in which growing goats were fed foliage from cassava  or Tithonia diversifolia (protein solubilities of 35 and 40%), supplemented or not with water spinach foliage (leaves plus stems) (protein solubility 76%).

Materials and methods

Location

The experiment was carried from May to July 2015 in the experimental farm of the Research and Technology Transfer Center, in Nong Lam University, which is located about 25 km from Ho Chi Minh City, Vietnam.

Experiment design

The experiment was designed as a 4*4 Latin Square (Table 1) with 10 day periods, 5 days adaptation to the diet and 5 days collection of feces and urine. The treatments were:

 TD : Tithonia diversifolia foliage alone

TD-WS: Tithonia diversifolia foliage plus water spinach 1% of LW as DM

CF: Cassava foliage alone

CF-WS: Cassava foliage plus water spinach 1% of LW as D M

Animals and management

Four growing male goats (Bach Thao breed) with body weight in the range from 10 to 13.5 kg and about 4-6 months of age were confined in cages made from wood and bamboo (width 0.6 m, length 0.8 m and height 0.8 m) with plastic mesh and plastic sheet beneath the floor to collect separately the feces and urine (Photo 1).

Photo 1. Metabolism cage made from wood and bamboo	Photo 2. The forages used in the experiment: Cassava, Tithonia and water spinach

Feeds and feeding system

Tithonia and cassava foliages were harvested from plots in which the forages had been established from cuttings one year previously and had been subjected to regular (every 2 months) defoliation. Water spinach was from the first or second harvest approximately 3 to 4 weeks after establishment from seed.  The Tithonia, cassava and water spinach were hung in bunches above the feed trough. The water spinach was resticted to an offer level of 1% of LW as DM; cassava and Tithonia were offered at approximatey 20% above recorded intakes.The foliages were offered twice daily: about 7.00am and 16.30pm. The cassava variety was a "sweet" variety, with  a relatively low concentration of hydrocyanic acid precursors (Phuong et al 2015).

Measurements

Intake, digestibility and N retention

Feeds offered and refused, and output of faeces and urine, were recorded daily during the last 5 days of each period. Samples of feed offered and refusals were taken daily. Feces were collected daily and stored in plastic bags in the refrigerator (4 °C). Urine was collected daily in a bucket to which was added 10 ml of 25% concentrated H₂SO₄ to maintain the pH at 4 or lower.

Methane emissions

At the end of each period, each goat was put in a bamboo frame box sealed with polyethylene film.  After 5 minutes to allow for the eructed gases to equilibrate with the air in the box, measurements were made of the concentrations of methane and carbon dioxide, over a 10 minute period, using an infra-red gas analyzer (Gasmet DX4000, Helsinki, Finland), following the method described by Madsen et al (2010).

Chemical analysis

Feed and feces samples were dried by microwave radiation to measure the DM content (Undersander et al 1993). Nitrogen in foliages, feces and urine was determined by the  Kjeldahl procedure as outlined in AOAC (1990).

Statistical analysis

The data were analyzed using the general linear model (GLM) procedure in the ANOVA program of the Minitab (2000) software. Sources of variation in the model were: animals, periods, main foliage (CF or TD), water spinach (with or without), the interaction main foliage*WS and error. 

Results and discussion

Foliage composition

Cassava and Tithonia foliage had similar crude protein content, slightly higher than in water spinach; the DM in water spinach was only one third of that in the other foliages (Table 2).  Protein solubility was twice as high in water spinach than in cassava or Tithonia.

Feed intake, apparent digestibility and N retention

DM intake was not affected by the main source of foliage nor by supplementation with water spinach (Table 3). Apparent DM digestibility was some 10% higher for diets based on Tithonia than on cassava foliage and was improved slightly (about 3%) when water spinach was also fed (Figure  1). Apparent digestibility of crude protein showed similar but smaller trends (Figure 2).  

There was a 21% increase in N retention when cassava was the main foliage rather than Tithonia (Figure 3), but the apparent (p=0.11) benefits by also giving water spinach were less (about 8%).  These advantages in favor of cassava foliage over Tithonia were reflected in the values for N rention as percent of N intake (Figure 4) and of N digested (Figure 5).

Figure 1. Apparent DM digestibility was higher for Tithonia than for cassava foliage, and slightly higher when water spinach was included in the diet	Figure 2. Apparent crude protein digestibility was higher for Tithonia than for cassava foliage, and slightly higher when water spinach was included in the diet	Figure 3. Daily N retention was higher for cassava than for Tithonia foliage, and higher when water spinach was added to the Tithonia foliage

Figure 4. Cassava foliage supported greater N retention as % of N intake, than Tithonia, with apparent benefits when water spinach was added to the Tithonia diet	Figure 5. Cassava foliage supported greater N retention as % of N digested, than Tithonia with apparent benefits when water spinach was added to the Tithonia diet

Methane: carbon dioxide ratios 

Methane emissions, measured as the ratio of methane to carbon dioxide, in the combined eructed gas-air mixture, were reduced by 50% when cassava rather than Tithonia was the main foliage (Figure 6). On both foliages, methane emissions were increased by water spinach, by about 30% on the cassava foliage and by 17% when Tithonia was the main foliage.

Figure 6. The ratio of methane to carbon dioxide in respired breath from the goats was reduced when Cassava rather than Tithonia was the forage source and was increased when water spinach was included in the diet

Discussion  

There is no obvious explanation for the lower N retention when Tithonia foliage rather than cassava was the basal diet , other than the greater solubility of the protein (40% in Tithonia versus 34% in cassava) resulting in a lower degree of protein escape from the rumen.  The fact that N retention was more closely linked with the apparent "escape" properties of the protein (higher in cassava than in Tithonia foliage) than with digestibility (lower in cassava) emphasizes the point made by Preston and Leng (1987) that it is the protein:energy ratio in absorbed nutrients which is the major determinant of animal production responses on tropical feeds. The increase in N retention in goats when Tithonia foliage was supplemented with mulberry foliage or with fermentable carbohydrate (cassava root chips) and urea (Pathoummalangsy Khamparn and Preston 2008) is further vidence that the supply of metabolizable protein from Tithonia is it's major limitation.

Water spinach has been shown to increase intake, digestibility and N retention in goats fed basal diets of foliages, high in tannins and of low digestibility, such as Mango (Kongmanila et al al 2011) and Bauhinia acuminata  (Silivong and Preston 2015a).  In the present experiment, water spinach supplementation led to increases in apparent digestibility of DM and crude protein and tended (p = 0.11) to improve N retention. Similar responses were reported when fresh water spinach was added to a basal diet of cassava foliage fed to growing goats (Pathoummalangsy Khamparn and Preston 2006).

The higher methane production per unit substrate fermented when Tithonia rather than cassava was the basal diet, and when water spinach was also fed, would appear to support the hypothesis that methane production is directly related to the rumen solubility of the protein.  Further evidence comes from in vitro rumen fermentations which showed consistent increases in methane production when water spinach was added to the substrate (Inthapanya and Preston 2014; Inthapanya et al 2015, 2016; Silivong and Preston 2015b).

A paradigm shift in modifying enteric methane production in ruminants

The hypothesis that feeds rich in insoluble protein (bypass protein) are associated with decreased production of enteric methane is supported by the assumption that on such feeds the balance of feed fermented in the cecum/large intestine relative to the rumen is increased. As acetogenic disposal of hydrogen in fermentative degradation in the cecum-colon appears to be dominated by acetogenesis (see Demeyer 1991; Immig 1996; Popova et al 2013; Leng 2016) this would account for decreased methane production on such diets.

Conclusions

• Appparent DM digestibility in growing goats was some 10% higher for diets based on Tithonia than on cassava foliage and was improved slightly (about 3%) when water spinach was also fed.
  
  
• There was a 21% increase in N retention when cassava was the main foliage rather than Tithonia , but the apparent benefits by also giving water spinach were less (about 8%).
  
  
• Methane emissions in eructed gas from goats were reduced by 50% when cassava rather than Tithonia was the main foliage in the diet.
  
  
• It is proposed that diets containg protein of low solubility would result in an increase in the balance of feed materials being digested in the cecum-colon region where acetogenesis plays a greater role then methanogenesis in the degradation of organic matter.

Acknowledgements

This research was done by the senior author as part of the requirements for the MSc degree in Animal Production "Improving Livelihood and Food Security of the people in Lower Mekong Basin through Climate Change Mitigation" in Cantho University, Vietnam. The authors acknowledge support for this research from the MEKARN II project financed by Sida.

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Received 12 December 2015; Accepted 2 April 2016; Published 1 May 2016

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