Effect of a supplement of fresh water spinach (Ipomoea aquatica) on feed intake and digestibility in goats fed a basal diet of cassava foliage

Pathoummalangsy Khamparn and T R Preston*

Faculty of Agriculture, National University of Laos (NUOL)
Vientiane, Laos
khamparnp@yahoo.com.au
^*Finca Ecológica, TOSOLY, UTA (Colombia)
AA #48, Socorro, Santander, Colombia
trpreston@mekarn.org

Abstract

The treatments in a 3*3 Latin square arrangement, with 3 goats and 3 periods each of 10 days, were three levels of water spinach fed as supplements to a basal diet of fresh cassava foliage. The levels were: WS0, only cassava foliage; WS1, Water spinach at 10 g DM per kg live weight plus free access to cassava foliage; WS2,  Same as WS1 but with water spinach at 20 g DM per kg live weight. Both the cassava foliage (offered ad libitum) and the water spinach were suspended in bunches hung from the top of the cage.

Urinary output increased linearly with degree of supplementation of water spinach and was three times greater on the WS2 diet compared with the control. Dry matter and N intake was increased linearly by supplementation with water spinach. The WS2 treatment resulted in water spinach providing 40% of the total diet DM, with double the overall feed intake compared with cassava alone. The effect of the water spinach was additive in that the intake of cassava in diets WS1 and WS2 was maintained at about the same level as in the cassava alone (WS0).  Supplementing the cassava foliage with water spinach increased digestibility of DM and crude fibre. There were no differences between the two levels of water spinach. N intakes did not differ between the two diets containing water spinach, both of which were higher than on the control (WS0) diet of cassava alone. Faecal and urine N were higher for the WS2 diet than for the WS0 and WS1 diets. The 50% higher intake of N on the diet with 40% water spinach was offset by the 300% greater N excretion in the urine, with the result that N retention was less with 40%  than with 26% or 0% water spinach in the diet.

Offering fresh water spinach at levels of 10 and 20 g DM per 1 kg live weight to goats having free access to fresh cassava foliage: did not affect intake of the cassava with the result that total DM intake increased by 33 and 60%, respectively; increased digestibility of DM and crude fibre; increased the rate of excretion of urine by factors of 1.7 and 3.2 compared with the control diet of cassava without water spinach. Increasing the level of water spinach from 26 to 40% of the diet DM increased DM intake by 25% but reduced N retention by 50%.

Key words: Cassava, digestibility, goats, intake, N retention, urine, water spinach

Introduction

The first report of successful use of fresh cassava foliage for ruminants was by Ffoulkes and Preston (1978). They  fed the fresh foliage as the sole supplement to a basal diet of a liquid mixture of  molasses and urea for fattening cattle. Growth rates were over 800 g/day and were not improved by feeding additional soya bean meal. More recently, Ho Quang Do et (2002) reported a curvilinear increase in feed intake and N retention in goats when fresh cassava leaves replaced grass as the supplement to untreated rice straw. Higher growth rates and reduced nematode infestation in goats, when cassava foliage rather than grass, was used to supplement brewers' grains were recorded by Seng Sokerya and Rodríguez (2003). Mom Seng et al (2001) observed increases in growth rate from 53 to 210 g/day, when fresh cassava foliage was fed to "Yellow" cattle on a basal diet of untreated rice straw.

In all the above reports the cassava foliage was fed as a supplement usually not exceeding 30% of the diet DM. Fresh cassava foliage was fed as the sole diet to goats by Theng Kouch et al (2003) but DM intakes and N retention were lower than on mulberry foliage even though DM digestibility was similar. The presence of cyanogenic glucosides and tannins could be the limiting factors to growth when fresh cassava is the sole component of the diet. In this case, improved performance could be expected by combining the cassava foliage with a feed containing low or zero content of these compounds. Working with pigs, fed a low-protein basal diet of broken rice, Chhay Ty and Preston (2005).showed that partial replacement (up to 50%) of cassava leaves by water spinach increased the DM intake and growth rate. Similar responses were observed at lower levels of replacement of 20 and 30% of cassava foliage by water spinach (Chhay Ty and Preston (2006).  

The objective of the present  study was to investigate the responses in goats when water spinach was offered as partial replacement of cassava foliage fed as the basal diet. The hypothesis was that feed intake and N retention would be improved when the cassava foliage was partially replaced by water spinach.

Materials and methods

Location

The experiment was carried out at the  Livestock Research Center (Nam Xuang village) of NAFRI, situated some 40 km from the capital city, Vientiane.

Treatments and experimental design

The treatments were three levels of water spinach fed as supplements to a basal diet of fresh cassava foliage. The levels were:

• WS0: Only cassava foliage

• WS1: Water spinach at 10 g DM per kg live weight plus free access to cassava foliage

• WS2: Same as WS1 but with water spinach at 20 g DM per kg live weight.

 The experimental design was 3*3 Latin square arrangement with 3 goats and 3 periods each of 10 days (Table 1).

Experimental animals, feeds and feeding system

The goats had initial live weights of 10.8, 10.9 and 11.9 kg. They were confined  in wooden cages designed to facilitate separate collection of  faeces and urine. The cassava foliage and water spinach were harvested from plots in the Livestock Research Centre. Cassava foliage was offered at 120% of recorded intake, with fresh quantities being provided 3 times per day. Samples of cassava foliage and water spinach were separated into leaves, petioles (for the cassava) and stems. Both the cassava foliage and the water spinach were suspended in bunches hung from the top of the cage (Photo 1). Fresh water was freely available.

Photo 1. Hanging the foliages in the cage

Measurements, sampling, data collection and chemical analysis

The goats were weighed at the beginning of each period. Feeds offered and refused were recorded and separated into component parts (leaves, petioles and stems). Urine and faeces were collected daily during the last 5 days of each period. The samples of feed offered and refused, urine and faeces were stored in a refrigerator; thereafter, all samples were mixed and representative amounts analyzed for N, ash and crude fibre by procedures of AOAC (1990). DM was estimated by micro-wave radiation (Undersander et al 1993).

Statistical analysis

The data were analysed using the GLM option of the ANOVA program in Minitab (2000) software (Minitab release 13.3). Sources of variation were treatments, animals, periods and error.
 

Results and discussion

Diet composition

The crude protein content was higher in the leaves of cassava than in those of water spinach (Table 2). 

Quantity and colour of urine

The appearance of the urine differed according to the degree of  supplementation with water spinach (Photo 2). This probably reflected the greater dilution of major urinary metabolites arising from degradation of the phenolic compounds (tannins) present in the cassava foliage.  Murdiati et al (2005) reported that the major urinary metabolites in sheep dosed with the hydrolysable tannin from Terminalia oblongata arose from the decarboxylation and reductive dehydroxylation of phenolics in the rumen, with the excretion of resorcinol glucuronide and the glucuronide of 2-carboxy-2'4'4,6,-tetrahydroxy diphenyl 2, 2'-lactone metabolites in the urine.

Photo.2. Characteristics of goat urine fed cassava foliage supplemented with
0 (WS0), 26 (WS1) or 40% (WS2) of water spinach (DM basis)

Urinary output increased linearly with degree of supplementation of water spinach and was three times greater on the diet with 40% of water spinach compared with the control (Figure 1). Similar increases in urine volume from feeding water spinach to goats were reported by Pheng Buntha and Preston (2006).

Figure 1: Output of urine as function of live weight according to degree of
supplementation of the cassava foliage with water spinach

Intake and digestibility

Dry matter and N intakes were increased linearly by supplementation with water spinach (Table 3; Figures 2 and 3). The WS2 treatment resulted in water spinach providing 40% of the total diet DM, with double the overall feed intake compared with cassava alone. The effect of the water spinach was additive in that the intake of cassava in diets WS1 and WS2 was maintained at about the same level as in the cassava alone (WS0).  Low feed intake by goats fed cassava foliage as the sole diet was also observed by Pheng Buntha and Chhay Ty (2006). Low palatability of foliages with high levels of tannins, as is the case in cassava (Wanapat et al 1997), has been ascribed to the astringent nature of tannins, and that this could be counteracted by supplementing with forages with high affinity for tannins (Reed et al 1982).  This could explain the beneficial effects of supplementing the cassava with the water spinach.

Nutrient digestibility

Supplementing the cassava foliage with water spinach increased digestibility of DM and crude fibre (Table 4 and Figure 4). There were no differences between the two levels of water spinach.  Tannins have been shown to depress digestibility of forages (Reed et al (1982; Murdiati et al 2005) thus the positive effects on DM and crude fibre digestibility may have been the result of the protein in the water spinach forming complexes with the tannins in the cassava, thus neutralising their otherwise negative effects on DM and fibre digestion.

Figure 4: Effect of supplementing cassava foliage with water spinach on digestibility
of dry matter, crude protein and crude fibre

Nitrogen balance

N intakes did not differ between the two diets containing water spinach, both of which were higher than on the control (WS0) diet of cassava alone (Table 5; Figure 5). Faecal and urine N were higher for the WS2 diet than for the WS0 and WS1 diets. The 50% higher intake of N on the diet with 40% water spinach was offset by the 300% greater N excretion in the urine, with the result that N retention was less with 40%  than with 26% or 0% water spinach in the diet. The inefficient utilization of the nitrogen in water spinach is apparent when data for DM intake are compared with those for N retention. DM intake increased by 25% when the water spinach proportion in the diets was raised from 26 to 40%, yet N retention was reduced by 50%. The implication from this finding is that the excretion of the excess N on the highest level of water spinach required additional expenditure of energy with the result that less energy was available for protein synthesis.

Figure 5: Balance of N in goats fed cassava foliage alone or with cassava replaced by
26 or 40% water spinach (DM basis)

Conclusions

• Offering fresh water spinach at levels of 10 and 20 g DM per 1 kg live weight to goats having free access to fresh cassava foliage:
  • Did not affect intake of the cassava with the result that total DM intake increased by 33 and 60%, respectively.
  • Increased digestibility of DM and crude fibre
  • Increased the rate of excretion of urine by factors of 1.7 and 3.2 compared with the control diet of cassava without water spinach
    
    

• Increasing the level of water spinach from 26 to 40% of the diet DM increased DM intake by 25% but reduced N retention by 50%.

 

Acknowledgements                                  

The senior author expresses her gratitude to SIDA-SARREC, for the opportunity to participate in the MEKARN Master of Science programme for countries in the Lower Mekong Basin, which provided the opportunity and the finance to do the research. Grateful thanks to Dr T R Preston and MSc Keansombath Lampheuy, for their advice and encouragement.  Special thanks are given to the Livestock Research Center (Nam Xuang) of the National Agriculture and Forestry Research Institute (NAFRI) for providing the facilities for conducting the experimental work.
 

References

 

AOAC 1990 Official Methods of Analysis: Association of Official Analytical Chemists. 15^th edition (K Helrick editor) Arlington pp 1230.

 

Chhay Ty and Preston T R 2005: Effect of water spinach and fresh cassava leaves on growth performance of pigs fed a basal diet of broken rice. Livestock Research for Rural Development. Volume 17, Article #76. Retrieved , from http://www.cipav.org.co/lrrd/lrrd17/7/chha17076.htm

 

Chhay Ty and Preston T R 2006: Effect of partial replacement of fresh cassava leaves by water spinach on growth performance of pigs fed a basal diet of broken rice. Livestock Research for Rural Development. Volume 18, in press

 

Ffoulkes D  and Preston T R 1978  Cassava or sweet potato forage as combined sources of protein and roughage in molasses based diets: effect of supplementation with soybean meal  Tropical Animal Production  3(3): 186-192 http://www.fao.org/ag/aga/agap/frg/tap33/3_3_1.pdf

 

Ho Quang Do, Vo Van Son, Bui Phan Thu Hang, Vuong Chan Tri and Preston T R 2002: Effect of supplementation of ammoniated rice straw with cassava leaves or grass on intake, digestibility and N retention by goats. Livestock Research for Rural Development (14) 3 http://www.cipav.org.co/lrrd/lrrd14/3/do143b.htm

 

Murdiati T B, McSweeney C S and Lowry J B 2005: Metabolism in sheep of gallic acid, tannic acid and hydrolysable tannin from Terminalia oblongata. Australian Journal of Agricultural Research. http://publish.csiro.au/paper/AR9921307.htm.

 

Mom Seng, Preston T R, Leng R A and U ter Meulen 2001 Effect of a single drench of cooking oil on the rumen ecosystem and performance of young local "yellow" cattle fed rice straw and cassava foliage. Livestock Research for Rural Development13 (4). Retrieved October 21, 2005, from http://www.cipav.org.co/lrrd/lrrd13/4/seng134.htm

Pheng Buntha and Chhay Ty 2006: Water-extractable dry matter and neutral detergent fibre as indicators of whole tract digestibility in goats fed diets of different nutritive value. Livestock Research for Rural Development. Volume 18, Article # 33. Retrieved, from http://www.cipav.org.co/lrrd/lrrd18/03/bunt18033.htm

Theng Kouch, Preston T R and Ly J 2003: Studies on utilization of trees and shrubs as the sole feedstuff by growing goats; foliage preferences and nutrient utilization. Livestock Research for Rural Development15 (7). Retrieved October 21, 2005, from http://www.cipav.org.co/lrrd/lrrd15/7/kouc157.htm

 

Wanapat M, Pimpa O, Petlum A and Boontao U  1997 Cassava hay: A new strategic feed for ruminants during the dry season. . Livestock Research for Rural Development 9 (2):  http://www.cipav.org.co/lrrd/lrrd9/2/metha92.htm