Chemical composition, digestibility and intake of some tropical foliage species used for goats

Daovy Kongmanila, T R Preston^* and Inger Ledin^**

Faculty of Agriculture, National University of Laos, Vientiane Capital, Lao PDR
^*Finca Ecológica, UTA-Colombia, AA #48, Socorro, Santander, Colombia
^*Department of Animal Nutrition and Management, Swedish University of Agricultural Sciences
P.O. Box 7024, 750 07 Uppsala, Sweden
daovyk@yahoo.com

Abstract

Two experiments were conducted to determine the chemical composition, feed intake, digestibility (in vivo and water extractable dry matter (DM)) and N retention of some tropical foliage species used for local goats in Laos.

In Experiment 1, 12 local male goats with an initial body weight (BW) of 14.6 kg and around 3.5 months of age, were randomly allocated to six treatments in a repeated randomized complete block design with 3 periods. Each period was 28 days long with 14 days of adaptation, 7 days of data collection and 7 days rehabilitation with good diets. The treatments were foliages from Erythrina (Erythrina variegata), Fig (Ficusracemosa), Jackfruit (Artocarpusheterophyllus), Jujube (Ziziphus jujuba Mill), Kapok (Ceiba pentandra) and Mango(Mangifera indica), which were offered ad libitum at the level of 130 % of the average daily feed intake. The Erythrina foliage had a low content of DM and condensed tannins (CT) and a high concentration of crude protein (CP) in leaves plus petioles, 193 g/kg DM, and stem, while the Mango foliage had a low CP, 69 g/kg DM, and high DM content. The other foliages were intermediate between Erythrina and Mango. High content of CT was found in the leaves plus petioles of Jackfruit foliage and in the stem of Fig and Mango foliage. There was a significant difference in feed intake, nutrient intake, apparent digestibility and N retention between treatments (P<0.05), with Erythrina, Jackfruit and Kapok foliage being significantly higher in those parameters than Fig, Jujube and Mango foliage. The water extractable DM could be used to predict N retention, but was not a good predictor of DM digestibility in this study.

In Experiment 2, 4 local male goats of 13.4 kg initial weight and 6 months of age were allocated to a 4*4 Latin square design, with 4 periods. Each period consisted of 10 days of adaptation to the diets and 5 days of data collection and with 3 days between each period for rehabilitation with good diets. The four treatments were: Water spinach ad libitum and Fig, Jujube or Mango ad libitum + 0.5% of BW as DM Water spinach. Water spinach had lower DM content and higher CP content compared to the other foliage species. Feed intake, apparent digestibility and N retention were not significantly different among the diets with foliages, but significantly higher than for water spinach alone (P<0.05).

Supplementation with water spinach to a diet consisting of low quality foliages such as Fig, Jujube and Mango, increased DM and CP intake, apparent digestibility and N retention, compared to feeding these foliages as sole feeds.

Key words: Feed intake, digestibility, N retention, Erythrina, Fig, Jackfruit, Jujube, Kapok, Mango, Water spinach, Foliage, Local goats

Introduction

Livestock is the most important source of protein food and family cash income of farmers in Laos, and also give manure for cropping in the rural areas. More than 70% of the total production from livestock such as goats, cattle, pigs and poultry comes from smallholders using traditional management systems. The main feed resources for the ruminants are native grasses, legumes and tree leaves that are available in the natural grassland and forests (Phengsavanh, 2003). According to Simbaya (2002) the feed resources that are available for animals are usually fibrous and low in most essential nutrients, including protein, minerals and vitamins.

The nutritive value of a feed is to a great extent a function of the chemical composition such as dry matter (DM), organic matter (OM), crude protein (CP), neutral detergent fiber (NDF) and acid detergent fiber (ADF). McDonald et al. (2002) reported that the digestibility of a feed is closely related to its chemical composition of which the fibre fraction has the greatest influence on the digestibility and both the amount and chemical composition of the fibre are important.

Modern methods of feed analysis attempt to distinguish fractions of cell walls and cell contents called NDF. When heated with neutral detergent solution, the cell contents dissolve and the cell walls remain as a residue. Another method that has been used to determine digestibility in vitro is the water extractable DM. It is essentially equivalent to the independent term in the equation proposed by McDonald (1981) cited by Ly and Preston (2001) for estimating protein digestibility for ruminants using the in sacco method, as described by Ørskov et al. (1980). Thu (2005) reported that the water extractable DM and in vivo DM digestibility in buffaloes were closely related to each other. Water extractable DM was a better predictor of digestibility than NDF according to Buntha and Ty (2006). There was a close relationship between water extractable DM and NDF, as shown by Chermiti et al. (1996). The water extractable DM is mostly derived from the cell contents, which in the NDF method is represented by the detergent soluble fraction. However, different forages have different water extractable DM (Ly and Preston, 1997), and the fresh leaves had a significantly lower value than the corresponding sun-dried samples.

There are many kinds of tree fodder, legumes and crops which are important protein resources, for instance foliage from Leucaena, Erythrina, Jackfruit, Kapok and Jujube, sweet potato vines and water spinach. Normally, these green plants are used as traditional feeds in diets for animals, but little is known about their nutritive value, especially the protein availability. Some foliages have been researched, but there are still many types of foliage commonly used as feeds that have not been characterized properly. For example foliage from Jackfruit (Artocarpusheterophyllus) has been extensively researched in tropical countries. According to Duyen et al. (1996), Jackfruit foliage can be used as a protein source for lactating goats and has a high intake potential (1640 g DM/d) compared to banana leaves and foliage from Trichanteragigantea and Acacia mangium when supplemented with rice straw and sugarcane tops as a basal diet. Keir et al. (1997) found that the intake of fresh Jackfruit leaves was 29% higher than Trichantera gigantea in goats, which is similar to the results reported by Nhan and Preston (1997). Intake of fresh Jackfruit leaves was higher when fed as a sole feed (3.9 kg/day) than when a supplement of sugar cane juice at levels up to 2 kg/day was given (3.5 kg/day) to dairy goats.

Also Erythrinavariegata has been studied to some degree. Simbaya (2002) reported that Erythrina contains 258 g CP and 14.4 MJ per kg DM, which is a high content of CP when compared to other fodder tree and shrub species. Aregheore and Perera (2004) and Kibria et al. (1994) suggested that Erythrina could be used as a protein supplement to improve the nutritional quality of maize stover fed to mature goats, since it has significantly higher digestibility of DM, CP, NDF, OM and energy than Leucaena and Gliricidia.

Kapok (Ceiba pentandra) is a multipurpose tree, which, as the fruit bursts open, exposes a cotton like substance. The seeds, leaves, bark and resin from the Kapok tree are used as traditional medicine for dysentery, fevers, venereal diseases, asthma, menstruation bleeding and kidney diseases. The leaves can be used for animal feed and contain 186 g CP and 884 g OM per kg DM. It has the potential to increase the DM digestibility and voluntary intake of low quality basal diets by supplying a valuable protein source (Kouch et al., 2005).

Mango (Mangiferaindica) is native to South Asia and is a multipurpose tree. The fruits and the foliage are not only used as food and feed but have also medicinal uses for humans. The foliage is a good potential source of forage to ruminants since it is green all the year round. According to Ajayi et al. (2005) Mango leaves contain 204 g CP/kg DM and when Mango leaves and concentrate were fed as a supplement to a Panicum maximum based diet, DM and CP intake increased as well as daily liveweight gain to 44.6 g/d

Some foliages are known to be preferred by goats e.g. Jujube (Ziziphusjujuba Mill), but there is little or no research available. According to Morton (1987) and Reich (1991) fresh Jujube leaves contain a saponin, ziziphin, and from dried leaves a sweetness-inhibiting saponin could be extracted. Nath et al. (1996) reported that Jujube leaves are a rich source of protein and minerals with 140 g CP, 28 g Ca and 1.4 g P per kg DM. Fig (Ficus racemosa) is also an available tree in tropical areas. Schurrie (1990) reported that Fig leaves are related to Jackfruit, Mulberry (Morus spp.) and Chinese Mulberry (Cudrania tricuspidata). According to data analysis from the Faculty of Agriculture Laboratory, NUoL, Laos, Fig foliage has high content of CP, 193 g/kg DM, and 170 g/kg DM of crude fiber.

Water spinach (Ipomoea aquatica) is another plant which produces high yields of protein-rich biomass. Water spinach has a high nutritive value for humans and also for animals such as rabbits (Samkol et al., 2006), pigs (Ty and Preston, 2005) and goats. According to Buntha and Ty (2006) the N intake of local goats was 8.84 g/day when fed fresh water spinach, which is higher than when feeding cassava foliage, guinea grass or stylo. Dry matter and N intakes were increased linearly by supplementation with water spinach by 40% compared to feeding cassava alone (Pathoummalangsy and Preston, 2006), and water spinach also increased DM digestibility and N retention in local goats.

The main limitation when using foliages as feed resources for ruminants is the content of anti-nutritional substances, of which the most important is tannin. Feeds with high tannin content may have detrimental effects on the performance of animals. According to Buntha and Ty (2006) high NDF content can also result in low DM digestibility.

The aim of this experiment was to analyse the chemical composition of some foliages available for goats and compare intake, digestibility (in vivo and water extractable) and nitrogen retention when feeding these foliages either as a sole feed or for foliages with low intake and digestibility, together with water spinach.

Material and methods

Location and climate

The experiments were conducted in the farm of the Livestock and Fisheries Department, Faculty of Agriculture, National University of Laos, 35 km south of Vientiane, Lao PDR. The climate in this area is tropical monsoon with a rainy season between May and October and a dry season from November to April. Average annual rainfall is 2000 mm/year. The two trials were conducted during June to December 2006.

Animals and management

The animals used in the two experiments were 16 local male growing goats, 12 goats for the first digestibility experiment and 4 goats for the second digestibility experiment. The goats were bought in the area around the Faculty of Agriculture, Nabong Campus. The mean and SD of the initial body weight (BW) of the goats was 14.6 (1.4) and 13.4 (2.2) kg, and the age around 3.5 and 6 months in the first and second experiment, respectively. Before starting the experiments, the goats were treated against parasites with injections of Ivermectin solution (1 ml per 4 kg BW) and were vaccinated against Foot and Mouth disease. Feed and water offered to each goat were weighed every morning and the animals were given the feed ad libitum at the level of 130% of the average daily feed intake the previous week. The animals were fed 3 times per day at 08:00 h, 12:00 h and 16:00 h. The minerals offered to each goat were given ad libitum by hanging a mineral block in each cage. The mineral lick block contained 140 g Na, 140 g Ca, 51 g P, 10.5 g S, 22 g K, 10 g Mg, 2.5 g Fe, 900 mg Zn, 350 mg Mn, 400 mg Cu, 90 mg Co, 380 mg I and 12 mg Se, per kg block.

The goats were housed in individual metabolism crates made from local materials measuring 0.8 x 0.8 x 0.8 m in width, length and height, respectively. The houses, cages and troughs were cleaned every day.

Experimental feeds

The experimental feeds used in the first digestibility experiment were foliages from Erythrina (Erythrina variegata), Fig (Ficus racemosa), Jackfruit (Artocarpus heterophyllus), Jujube (Ziziphus jujuba Mill), Kapok (Ceiba pentandra) and Mango(Mangifera indica). In the second digestibility experiment, the feeds used were Water spinach(Ipomoea aquatica), Fig, Jujube and Mango.

Each foliage was used in the fresh form, including leaves, petioles and 30 cm of the stem. The foliages were offered hanging, tied to a bamboo stick over the cage and above the feed trough to collect leaves that may have fallen down. The foliages were harvested by cutting trees and shrubs around the Faculty of Agriculture in the morning for feeding at noon and in the afternoon for feeding the next day in the morning. The water spinach was bought from farmers around the Faculty of Agriculture in the morning and weighed for feeding during the whole day.

Experimental design

The first digestibility experiment was a repeated randomized complete block design (RCBD) with 6 treatments (the different foliages fed as the sole feed). The experiment was run for 3 periods (3 repetitions) and each period had 2 blocks. The goats were randomly allocated to the metabolism cages and the foliages. In every period, each foliage was given to 1 animal in each block. The periods consisted of 14 days of adap

The second digestibility experiment was a 4*4 Latin Square design.The treatments were four diets: 1: Water spinach ad libitum (WS), 2: Fig ad libitum + 0.5% of BW as DM Water spinach (FWS), 3: Jujube ad libitum + 0.5% of BW as DM Water spinach (JWS) and 4: Mango + ad libitum + 0.5% of BW as DM Water spinach (MWS). Half of the daily offer of Water spinach was fed at 08:00 h in the morning and half at 16:00 h in the afternoon. Each period of the experiment consisted of 10 days of adaptation to the diets and 5 days of data collection and between each period there was a 3 day period for rehabilitation, with good diets such as grass, cassava chip and some foliage provided.

Measurements and analyses

Feeds offered and refused were recorded individually daily during the whole experimental period. Each foliage, six samples in the first experiment and eight samples in the second experiment, was separated and weighed to estimate the average proportion of leaves plus petiole and stem. During the collection period the refusals were separated into leaves plus petiole and stem in order to measure the selection of the different parts. Water offered and refused was also measured daily.

Samples of feed offered were taken twice in each period, resulting in 6 and 8 samples of leaves plus petiole and stem in total in the first and second experiment, respectively. The whole foliage was sampled (divided into leaves plus petiole and stem). Samples of refusals (also divided into leaves plus petiole and stem) were taken individually daily during the data collection periods. The faeces and urine excreted were recorded twice daily at 7:00 h and 17:00 h. At each data collecting time, 10% of the faeces was sampled and frozen at -20^oC. Urine was collected in a jar containing 50 ml of 10% sulphuric acid (urine pH<3) to preserve the nitrogen (Chen and Gomes, 1992) and 10% urine was also sampled and stored at 4^oC for further analysis.

The fresh form of the foliages was analysed for DM, ash, and CP according to AOAC (1990). NDF was determined using the procedure of Goering and Van Soest (1970). Condensed tannins were analysed according to Makkar et al. (1995) and water extractable DM by the method described by Ly and Preston (1997).

When analysing the water extractable DM and N the samples were dried in a micro-wave oven (Undersander et al., 1993) to constant weight and were then ground in a coffee mill. A sample of about 2-3 g of the dry ground material was put in weighed nylon bags, with the size 50 x 150 mm, and with a pore size of 45 to 55 µm. The bags containing the samples were tied and put into a washing machine with 3 litres of water per bag. Washing was done for 90 minutes with 15 minutes in each cycle. After washing, the bags were dried and weighed (Ly and Preston, 1997).

Statistical analysis

The data from the intake and digestibility trials were analyzed statistically by using the GLM procedure of Minitab Software, version 13.31 (Minitab, 2000). Treatment means, which showed significant differences at the probability level of P<0.05, were compared using Tukey's pair-wise comparison procedures.

In the first experiment, the statistical model used was: Y_ijk = m + P_i + B_j(P_i) + F_k + e_ijk where Y_ijk is the dependent variable, P_i is the effect of period, B_j(P_i)is the effect of block in the period, F_k is the effect of treatment (different foliages) and e_ijk is the random error effect.

In the second experiment, the statistical model used in the analysis was: Y_ijk = m + F_i + A_j + P_k + e_ijkwhere Y_ijk is the dependent variable, F_i is the effect of treatment, A_j is the effect of animals, P_jis the effect of period and e_ijk is the random error effect.

Results

Experiment 1

Feed offered and feed intake for the six foliages are shown in Table 2. Total DM offered of Jackfruit foliage (965 g DM) was significantly higher than for Erythrina, Fig, Jujube and Mango foliage, but similar to DM offer of Kapok foliage. The total DM intake of Jujube and Mango foliage was lowest, 380 g and 393 g, respectively, significantly different from Jackfruit (with the highest intake of 650 g), Erythrina, and Kapok foliage, but similar to the intake of Fig foliage. Feed intake expressed in percent of BW varied from 2.5% to 4.4%, the highest for Jackfruit and lowest for Jujube.

Table 2. Least squares means for feed offered and feed intake
	Erythrina	Fig	Jackfruit	Jujube	Kapok	Mango	SEM
Feed offered, g fresh/day
Leaves + petioles	3123a	1856bc	2064b	1452c	2157b	1216c	137.0
Stem	865a	870a	983a	476b	867a	475b	63.4
Total	3988a	2726b	3048b	1929c	3024b	1691c	141.6
Feed offered, g DM/day
Leaves + petioles	617ab	534ab	662a	501b	639ab	560ab	33.5
Stem	164b	201b	303a	180b	200b	171b	17.9
Total	781b	734b	965a	681b	838ab	731b	39.5
Feed intake, g DM/day
Leaves + petioles	516a	428ab	558a	316b	536a	331b	34.2
Stem	97	58	92	64	73	62	14.8
Total	613ab	485bc	650a	380c	609ab	393c	37.6
Feed intake in % of feed offered
Leaves + petioles	84a	80ab	85a	63bc	85a	57c	4.4
Stem	57a	30b	30b	34ab	37ab	34ab	5.9
Total	79a	66ab	68ab	56bc	73ab	51c	3.4
Feed intake in % of BW
Leaves + petioles	3.4a	2.9ab	3.8a	2.1b	3.3a	2.2b	0.2
Stem	0.6	0.5	0.6	0.4	0.5	0.5	0.1
Total	4.0ab	3.4bc	4.4a	2.5c	3.8ab	2.7c	0.2
Water intake, g/day	94	195	201	194	142	192	49.2
a,b,c Means within rows with different superscripts differ at P<0.05

Water intake varied from 94 g 201 g/day, but was not significantly different among foliages. Feeding Erythrina foliage resulted in significantly higher CP intake, 109 g/day, compared to the other foliages. The lowest CP intake was obtained with Mango foliage, 25 g/day (Table 3) The apparent digestibility of DM, OM, NDF and CP, and the N retention, were generally higher for Erythrina, Jackfruit and Kapok foliage than for Fig, Jujube and Mango foliage.

Table 3. Least squares means  for intakes of proximate constituents, apparent digestibility and N retention
	Erythrina	Fig	Jackfruit	Jujube	Kapok	Mango	SEM
Intakes from leaves + petioles, g/day
CP	100a	51b	64b	30c	65b	22c	4.3
NDF	240ab	207ab	257a	141bc	269a	165bc	16.8
OM	463ab	365b	503a	294bc	479a	312bc	31.5
Intakes from ítem, g/day
CP	9a	4b	5ab	4b	4b	3b	0.9
NDF	51	30	50	37	40	35	8.4
OM	88	53	80	62	65	58	13.7
Total intake, g/day
CP	109a	55b	69b	34c	69b	25c	4.2
NDF	291ab	238ab	307a	179bc	309a	200bc	19.5
OM	551ab	418b	583a	356bc	543a	370bc	35.2
Apparent digestibility, g/kg
DM	615a	466b	514ab	527ab	572ab	486ab	31.9
CP	731a	238c	542ab	387bc	660a	248c	54.0
NDF	542a	319b	394ab	336b	505a	341b	40.3
OM	641a	500b	569ab	556ab	600ab	519ab	30.7
N balance, g/day
Intake	17.4a	8.8b	11.1b	5.4c	11.0b	4.0c	0.7
Faeces	4.7abc	6.3a	5.1ab	3.1c	3.6bc	2.9c	0.4
Urine	8.6a	1.1c	3.2b	1.1c	3.9b	0.6c	0.4
Retention	4.1a	1.4bc	2.9ab	1.1c	3.5a	0.5c	0.4
a,b,cMeans within rows with different superscripts differ at P<0.05

The changes in live weight throughout the experiment ranged from a negative value of -26.2 g/day for the Mango foliage to 85.7 g/day for the Jackfruit foliage (Table 4).

Table 4. Least squares means  for live weight at the start and weight changes during the digestibility experiment
	Erythrina	Fig	Jackfruit	Jujube	Kapok	Mango	SEM
Weight at start, kg	15.0	14.5	14.7	15.2	15.9	14.2	0.5
Weight change, g/day	78.6	16.7	85.7	9.5	57.1	-26.2	41.2

 

The relationships between water extractable DM (WDM)  and N retention, and between NDF and N retention, are shown in Figures 1 and 2. The relationship was much stronger when WDM was the independent variable, as compared with NDF. The relationships were poorer when the dependent variable was apparent DM digestibility (Figures 3 and 4), but was closer for WDM than for NDF as independent variables. .

Figure 1. Relation between NDF in the foliages and N retention (The different points are the means of each of the 6 foliages in the experiment)	Figure 2. Relation between water extractable DM (WDM) in the leaves + petioles of the  foliages and N retention (The different points are the means of each of the 6 foliages in the experiment)

Figure 3. Relation between NDF in the leaves and petioles of the foliages and apparent DM digestibility  (The different points are the means of each of the 6 foliages in the experiment)	Figure 4. Relation between Water extractable DM (WDM) in the leaves and petioles of the foliages and apparent DM digestibility  (The different points are the means of each of the 6 foliages in the experiment)

Experiment 2

The DM content of leaves plus petioles and stem ranged from 86 g and 47 g/kg in the water spinach to 446 g and 352 g/kg in the Mango foliage (Table 5). The CP content in water spinach was high, 249 g and 126 g/kg DM, for leaves plus petioles and stem, respectively.

Table 5.  Least squares means and (SD) for 6 samples of each foliage for chemical composition and relation between stem and leaves of the foliages
	Water spinach	Fig	Jujube	Mango
Fresh, g/kg
Leaves + petioles	391 (51.7)	630 (116.3)	646 (109.4)	688 (56.5)
Stem	609 (51.7)	370 (116.3)	354 (109.4)	313 (56.5)
As DM, g/kg
Leaves +petioles	547 (87.2)	690 (107.0)	654 (135.8)	736 (65.9)
Stem	454 (87.2)	310 (107.0)	346 (135.8)	265 (65.9)
In leaves+ petioles
DM, g/kg	86 (6.0)	276 (59.3)	330 (54.7)	446 (39.2)
In g/kg DM
CP	249 (19.3)	131 (21.7)	137 (24.3)	87 (14.1)
NDF	448 (23.6)	471 (50.3)	491 (29.8)	428 (40.1)
OM	826 (33.0)	847 (24.6)	936 (26.7)	935 (29.0)
In stem
DM, g/kg	47 (12.5)	215 (69.8)	320 (70.1)	352 (63.6)
In g/kg DM
CP	126 (10.6)	76 (15.7)	76 (21.1)	69 (5.5)
NDF	398 (22.5)	519 (58.7)	579 (39.1)	488 (38.6)
OM	797 (36.2)	919 (25.8)	963 (14.9)	949 (22.1)

The DM intakes were similar when the the three tree foliages were supplemented with water spinach and much less for the diet with water spinach alone (Table 6)..

Table 6. Least square means for feed offered and feed intake
	WS	FWS	JWS	MWS	SEM
Feed offered, g fresh
Foliage	0	2500a	2148ab	1600b	128.2
Water spinach	5428a	945b	993b	924b	61.0
Total	5428a	3445b	3140bc	2524c	155.0
Feed offered, g DM
Foliage	0	633	696	659	58.2
Water spinach	336a	59b	61b	57b	4.7
Total	336b	692a	757a	716a	58.0
Feed intake, g DM
Foliage	0	444	461	399	39.4
Water spinach	246a	57b	44b	52b	6.0
Total	246b	501a	505a	451a	40.5
Feed intake in % of feed offered
Foliage	0	69	68	61	2.2
Water spinach	73b	97a	72b	91a	2.6
Total	73a	72a	68ab	63b	1.3
Feed intake in % of BW
Foliage	0	3.3	3.3	3	0.2
Water spinach	2.0a	0.4b	0.3b	0.4b	0.02
Total	2.0b	3.7a	3.6a	3.4a	0.2
Water intake, g/day	31	114	29	36	21.2
a,b,c Means within rows with different letters differ at P<0.05 WS: Water spinach ad libitum FWS: Fig ad libitum + 0.5 % BW as DM of water spinach JWS: Jujube ad libitum + 0.5 % BW as DM of water spinach MWS: Mango ad libitum + 0.5 % BW as DM of water spinach

The CP intake in the JWS diet was highest (66 g), significantly different from the water spinach diet (48 g) and the MWS diet (43 g) but similar to the FWS diet (65 g). Both OM and NDF intake from water spinach as a sole feed were significantly lower than for the JWS, FWS and MWS diets. The apparent digestibility of DM, CP and NDF of the water spinach diet was significantly higher compared to the other diets. N retention ranged from 2.0 g to 3.1 g per day and did not differ among diets. When the N excretion was adjusted by covariance for differences in N intake, faecal N was lower and urine N higher on the diet of water spinach alone compared with the foliages supplemented with water spinach. N retention expressed as a proportion of N intake did not differ among treatments. However, expressed as a proportion of N digested, the values were lower for the water spinach alone than for the foliages supplemented with water spinach.

Table 7. Least square means for intake of proximate constituents, apparent digestibility and N retention
	WS	FWS	JWS	MWS	SEM
Nutrient intake, g/d
From foliage
CP	0	54a	58a	33b	3.6
NDF	0	211	235	173	18.1
OM	0	360	410	343	35.0
From water spinach
CP	48a	11b	8b	10b	1.7
NDF	105a	24b	19b	22b	3.0
OM	201a	46b	36b	43b	5.9
Total
CP	48ab	65a	66a	43b	4.1
NDF	105b	235a	254a	195ab	18.9
OM	201b	406a	445a	385a	38.1
Apparent digestibility, g/kg
DM	762a	611b	644ab	624ab	29.5
CP	794a	441b	575b	547b	41.1
NDF	717a	464b	513ab	440b	45.3
OM	774	612	639	604	36.5
N balance,  g/day
Intake	7.7ab	10.5a	10.6a	6.9b	0.6
Faeces	1.6b	5.8a	4.4ab	3.1b	0.6
Urine	4.1a	1.7b	3.0ab	1.8b	0.3
Retention	2.0	2.9	3.1	2.1	0.3
Faecal#	2.04c	5.29a	3.81b	3.85b	0.19
Urine#	4.26a	1.53d	2.80c	2.01bd	0.14
Retained#	2.10	2.31	3.07	2.62	0.24
N ret/N intake	0.287	0.296	0.283	0.263	0.025
N ret/N digested	0.614a	0.484b	0.502ab	0.331c	0.032
a,b,c Means within rows with different letters differ at P<0.05 # Adjusted for differences in N intake WS: Water spinach ad libitum FWS: Fig ad libitum + 0.5 % BW as DM of water spinach JWS: Jujube ad libitum + 0.5 % BW as DM of water spinach MWS: Mango ad libitum + 0.5 % BW as DM of water spinach

All the goats gained in weight during the experiment (Table 8).

Table 8. Least squares means for initial weight and weight changes during experiment 2
	WS	FWS	JWS	MWS	SEM
Weight at start, kg	12.2b	13.7ab	14.2a	13.3ab	0.3
Weight change, g/day	20	40	50	30	52.0
a,b,cMeans within rows with different letters differ ar P<0.05 WS: Water spinach ad libitum FWS: Fig ad libitum + 0.5 % BW as DM of water spinach JWS: Jujube ad libitum + 0.5 % BW as DM of water spinach MWS: Mango ad libitum + 0.5 % BW as DM of water spinach

Discussion

Experiment 1

Feed composition and intake

The foliage from Erythrina had a high CP content. This is probably due to the fact that Erythrina is the only one of the studied plants that belongs to the Leguminosae family and consequently has the ability to fix nitrogen. Many authors have found that Erythrina has a high CP content compared to other foliages e.g. Acacia, Fig, Jackfruit, Gliricidia, Leucaena, Mango, Sesbania and Tamarind (Kibria et al., 1994; Baidya et al., 1995; Simbaya, 2002; Aregheore and Perera, 2004; Gregorio et al., 2005). However, on these reports, the results reported on CP content for  Erythrina leaves (205 g to 258 g/kg DM) are higher than the value from this study (193 g/kg DM). This could possibly be due to different ages of the trees or the shoots, the season for collecting samples or different varieties.

The content of condensed tannins in Jackfruit leaves plus petioles was 130 g/kg DM, much higher than the 36 g/kg DM of total tannins recorded by Mui et al. (2001) and 51 g/kg DM of total tannins obtained by Van et al. (2005). The methods of analysis are different, but total tannins should be the same or higher than condensed tannins, which are only one fraction of the total tannins. The way the samples are treated before analysis is very important e.g. drying at a temperature higher than 45^oC will result in lower tannin values, since the tannins will be strongly bound to protein and fibre (Palmer et al., 2000). However, Mui et al. (2001) and Van et al. (2005) also showed that the Jackfruit foliage had a higher content of tannins than other foliages and that the tannin content of the leaves was higher than in the stems, which is in agreement with the present study.

The foliages showing the highest intake were Erythrina, Jackfruit and Kapok. The major difference  in the analysed chemical components between these foliages and the three foliages with inferior intake characteristics (Mango, Jujube and Fig) was in the CP content which was especially low for Jujube and Mango The tannin content was highest in Jackfruit and Jujube and not very high in Mango and did not seem be a determining factor for feed intake. The DM intake of Mango was lowest of all foliages, at 2.7% of BW. Kibria et al (1994) also found a low intake of Mango leaves (2.9% of BW) in Black Bengal goats. The differences in feed intake can be due to other factors e.g. structure of the leaves, soft versus hard, and smooth versus waxy or hairy, content of substances causing the foliages to smell or taste distinctly, or morphology of the plants resulting in different bite sizes (Van 2006).

The highest DM and CP digestibility and N retention were obtained when feeding Erythrina, Jackfruit and Kapok foliages. These results are supported by Kibria et al. (1994), Baidya et al. (1995), Mui et al. (2002), Lin et al. (2003), Aregheore and Perera (2004), Van et al. (2005) and Phengvilysouk and Kaensombath (2006). The digestibility of DM did not seem to be closely related to tannin content, and McSweeney et al. (1999) also found that tannin content was poorly correlated with digestibility of DM and N in foliages from some Leucaena varieties and Calliandra. The requirement for a goat weighing 15 kg and growing at 75 g/day is 79 g CP or 50 g digestible CP according to Mandal et al. (2005). This means that the consumption of Erythrina, Jackfruit and Kapok covered the CP requirements of the goats while the other foliages did not. When considering the high digestibility of CP in Erythrina the goats consumed 160% of the requirement of digestible CP. Probably there was a lack of energy that prevented the goats from growing faster in spite of the fact that there was CP available but they could also have reached their genetic capacity for growth. According to Phengvichith (2007) local goats from Laos offered a diet high in energy and protein and dewormed gained 92 g/day. However, care should be taken not to draw any consistent conclusions about growth rate, since the period of feeding each foliage was too short for a proper evaluation.  

Water extractable DM as a method for estimating nutritive value

The fact that water extractable DM was a better predictor of N retention than NDF is to be expected as the former is a direct measure of the more easily fermentable nutrients (assumed to be the soluble nutrients and small particles). Relationships with apparent DM digestibility were poorer than with N retention but still comparatively better for water extractable DM than for NDF.  These findings are supported by the reports from Nguyen Van Thu (2005) and Pheng Buntha and Chhay Ty (2006)  of  high relationships (R²= 0.91 and R²= 0.98)  between water extractable DM and DM digestibility in swamp buffaloes and goats, respectively. Comparable relationships between NDF and apparent DM digestibility were weaker (R²=0.74; Pheng Buntha and Chhay Ty 2006). 

Experiment 2

Chemical composition of feeds and diets

The leaves plus petioles and stem of water spinach had a higher CP content (249 g and 126 g/kg DM, respectively) compared to Fig, Jujube and Mango foliage. The CP levels were similar to the results of Pathoummalangsy and Preston (2006) and Phiny and Kaensombath (2006), but lower than the values 262 g to 278 g/kg DM of leaves plus petioles reported by Buntha and Ty (2006) and Samkol et al. (2006). The higher CP levels reported by these authors can be due to harvesting age of the water spinach or nutrients available in the soil e.g. through supply of fertilizer. The water spinach also had a low DM content, which has also been noted by other authors (Pheng Buntha and Chhay Ty, 2006; Hiep and Preston, 2006; Hue and Preston, 2006; Pathoummalangsy Khamparan and Preston, 2006; Chiev Phiny and Kaensombath Lampheuy, 2006; Pok Samkol et al., 2006)

Feed intake, digestibility and N retention

Table 9. Comparison of feed intake and N retention when tree foliages with apparently low nutritive value (Exp 1) were supplemented with fresh water spinach at 0. 5% of live weight as DM (Exp 2)
	Mango	Jujube	Fig
DM intake, % LW
Without water spinach (Exp 1)	2.7	2.5	3.4
With water spinach (Exp 2)	3.4	3.6	3.7
N retention, g/day
Without water spinach (Exp 1)	0.5	1.1	1.4
With water spinach (Exp )	2.1	3.1	2.9

Pathoummalangsy and Preston (2006) also found that feed intake and digestibility increased to double the overall values, when supplementing cassava foliage with water spinach (2% of BW), compared to feeding cassava alone. This coul be due to the increased level of protein in the small intestine if the proteins in the water spinach form complexes with the condensed tannins in the foliages (Reed et al. 1982).
 

Conclusions

• The Erythrina, Jackfruit and Kapok foliages had better intake characteristics, CP digestibility and N retention than Fig, Jujube and Mango foliages.

• Water spinach can be used as a supplement to the foliages of lower quality to increase DM and CP intake, apparent digestibility and N retention.

• The water extractable DM as a method of analysis can be used to predict N retention.

Acknowledgements

The authors gratefully acknowledge the Swedish International Development Agency/ Department for Research Cooperation with Developing Countries (Sida/SAREC) for financial support of this research, the Faculty of Agriculture, National University of Laos for making the facilities available and the four students of HD₃ (12^th Generations) in this institution for taking care the goats. Thanks are also due to Dr. Xe for statistical advice.

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