The nutritive value of Hibiscus rosa siensis silage and the effect of supplement levels on feed intake, digestibility, N-retention and rumen environment of sheep and goats

Nguyen Xuan Ba, Vu Duy Giang, Le Duc Ngoan and Vu Chi Cuong

Hue University of Agriculture and Forestry
Hue, Vietnam
nthanhhuong@dng.vnn.vn

Abstract

Hibiscus rosa-sinensis L belongs to Malvacea family. The farmers in central Vietnam mainly use it as a live fence and ruminant feed. Due to high biomass yield (about 10 tonnes of DM leaves/year/ha) and high crude protein content (17-21%), hibiscus foliage could be a protein supplement source for ruminants. The experiments aimed to evaluate nutritive value of Hibiscus rosa-sinensis L and effect of supplemental levels of Hibiscus rosa-sinensis L silage (HS) on DM intake, digestibility, N retention and rumen environment of goats and sheep. The nutritional values were evaluated in term of chemical composition, in vitro gas production (GP) and were calculated following the INRA system. The first experiments were designed as a Latin square with 4 local growing goats with a mean live weight of 15.3 kg. The treatments were (HS0) natural grass ad libitum (basal diet), (HS 0.4) basal diet plus 0.4 kg HS, (HS 0.6) basal diet plus 0.6 kg HS and (HS 0.8) basal diet plus 0.8 kg HS. The second experiment was designed also as a Latin square (5 x 5) with 5 local growing sheep with an average live weight of 17.4 kg. The treatments were: (HS0) King grass ad libitum (basal diet), (HS 400) Basal diet plus 400g Hibiscus rosa siensis foliage silage, (HS 600) Basal diet plus 600 g HS; (HS 800) Basal diet plus 800 g HS and (HS 1000) Basal diet plus 1000 g HS.

The results from the experiment showed that the Hibiscus rosa foliage silage had a high content of CP (20-21% in DM) and high palatability for goats and sheep. Parameters of in vitro gas production showed there was no difference between the sample with or without addition of PEG. The gas volume at 48 hours after incubation was 46.5 and 46.6 ml in the sample without and with PEG, respectively. The first experiment showed that there e significant differences in DM intake, digestibility of DM, OM and CP among the diets. There was a trend to increasing intake and digestibility of goats when increasing Hibiscus rosa silage in the diets up to 40%. There were no differences in the goat's rumen environment between the diets.

The results from the second experiment showed that ME and PDI of Hibiscus foliage silage were 2738 kcal and 148 g per kg of DM, respectively. The in vivo DM, OM and CP digestibility values of Hibiscus foliage silage were 69.7, 73.1 and 84.4%, respectively. There were differences in dry matter intake, digestibility and N retention between treatments. The determinant coefficients (R²⁾ between DM, OM, CP digestibility and percentage of Hibiscus foliage silage in the ration were 0.43, 0.45 and 0.37, respectively. The N retention was increased when increasing Hibiscus foliage silage percentage in the diets.

The Hibiscus foliage silage could be a good supplement as protein sources for ruminant.

Key words: chemical composition, digestibility, gas production, goats, hibiscus rosa siensis, N- retention, PEG, silage, sheep, supplement,

Introduction

Hibiscus rosa siensis L. belongs to the Malvacae family. The farmers in central Vietnam mainly use it as a live fence and ruminant feed. Hibiscus plants can grow very well in different kinds of soil and they can withstand hard conditions (hot weather and drought) in Central Vietnam (Nguyen Xuan Ba and Le Duc Ngoan 2003). The hibiscus leaves have high crude protein content (17-22% in DM) and high palatability for goats and sheep. Hibiscus can be planted by stem cuttings and it thus is easy to expand. In recent years, there has been some research on making silage of tree foliage (Nguyen Xuan Ba et al 2004a,b; Ojeda et al 2000). Sheep were used as the means for determination of in vivo digestibility because they have similar digestibility index with cattle (Aerts et al 1984).

Objectives:

To determine the nutritive value of Hibiscus rosa siensis foliage silage for growing goats and sheep.
To measure the effects of different amounts of Hibiscus rosa siensis foliage silage on the intake of a basal diet of grass and to estimate substitution rate of supplement for forage.
To measure the effects of different amounts of Hibiscus rosa siensis foliage silage on diet DM, OM and CP digestibility and rumen environment of goats.

Materials and methods

Location and feeds

The experiments were conducted from March to December 2003 in Hue University of Agriculture and Forestry (HUAF). The Hibiscus rosa siensis foliages were collected around Hue city and were ensiled with 5% of molasses. Native grasses were cut around Hue City. Elephant grass was harvested after re-growth period of 30-35 days in the HUAF farm.

Experiment 1: Effect of Hibiscus rosa siensis silage levels in the diet on feed intake, digestibility and N-NH₃ content in the rumen fluid of goats

Experimental design and animals

Four local growing goats with average body weight of 17.4 kg were used to study the feed intake, total tract digestibility and N-retention of the diets. The experiment was designed as a 4x4 Latin square. Each period lasted 15 days, in which 10 days were for adaptation, 5 days for data collection. The diets were native grass (NG) (basal diet) (HS0), basal diet plus 400 g/day Hibiscus rosa siensis foliage silage (HS400), basal diet plus 600 g/day Hibiscus rosa siensis foliage silage (HS600), basal diet plus 800 g/day Hibiscus rosa siensis foliage silage (HS800). Water and salt were freely available for all animals. Feeding was 4 times per day at 8, 11, 14 and 17 o'clock. The animals were kept in digestibility cages in order to collect the samples of faeces.

Experiment 2: Effect of Hibiscus rosa siensis silage levels in the diets on feed intake, digestibility and N-retention of sheep.

Five local growing sheep with average body weight of 15.3 kg were used to study the feed intake, rumen environment and total tract digestibility of the diets. The experiment was designed as a 5 x 5 Latin square. Each period lasted 16 days, in which 10 days were for adaptation, 5 days for data collection and day 16 for taking the sample of rumen fluid. The diets were Elephant grass (basal diet) (HS0), basal diet plus 400 g/day Hibiscus rosa siensis foliage silage (HS400), basal diet plus 600 g/day Hibiscus rosa siensis foliage silage (HS600), basal diet plus 800 g/day Hibiscus rosa siensis foliage silage (HS800) and basal diet plus 1000 g/day Hibiscus rosa siensis foliage silage (HS1000). Water and salt were freely available for all animals. Feeding was 4 times per day at 8, 11, 14 and 17 o'clock. The animals were kept in digestibility cages in order to collect separately the samples of faeces and urine.

Sample collection

Hibiscus rosa siensis foliage samples were collected from the HUAF farm after re-growth of 10 weeks, chopped into small pieces, dried in an oven at 60^°C and then ground for gas production analysis.

Feed 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 and analyzed for DM and N

Faeces were collected every 2 hours and put in polyethylene bags and stored at 4 ^ºC. At the end of each period the total amount of faeces were mixed and a sub-sample (about 10%) was then dried at 60^ºC for chemical analysis. Rumen fluid was taken by stomach tube 4 hours after feeding on day 16. At each time, about 20 ml of rumen fluid were obtained. 10% of solution of 20 % H₂SO₄ was added to halt the fermentation. Urine were immediately collected after urinating, added 10% of solution of 20 % H₂SO₄ and then stored at -20⁰C . At the end of each period all the urine of each animal was mixed well and 10 % of sub-sample taken for chemical analysis.

Measurements and chemical analysis

Total N of feed, faeces and urine and N-NH₃ of feed and rumen fluid were measured by the Kjeldahl procedure as outlined by the AOAC (1990). The ash content of feed and faeces was determined following the AOAC (1990) recommendations. Organic matter was assumed to be the result of subtracting the percentage of ash from 100. pH was determined by glass electrode measurements in a digital pH meter. Gas production was determined following the in vitro procedure of Menke and Staingass (1988).

The digestibility of Hibicus rosa foliage silage in the in vivo experiment was calculated following the equation:

Where:

Z : Digestibility for DM, OM and CP of HS (%)
Y: Digestibility for DM, OM, CP of diet which contained HS (%)
X: Digestibility for DM, OM, CP of elephant grass (%)
a : percentage of grass in the diet based DM; OM or CP
b :percentage of hibiscus rosa foliage silage in the diet based DM; OM or CP

Biometrical analysis

The data were analyzed according to the analysis of variance technique using the general linear model (GLM) procedure in the software of MINITAB version 13 The mathematical model used was:

Y_{i jk} = M + P_i + A_j + T_(i
j),K + E_{i jk}

Where:
Y_{i jk} : Independent variable (intake, apparent digestibility....)
M: Overall mean
P_i: Effect of period
A_j:: Effect of goats
T_k: Effect of treatments
E_i _jk: Effect of random error

Results and discussion

Gas production of Hibiscus rosa siensis foliages

Gas volumes and gas production indices from 200 mg DM of Hibiscus rosa siensis foliage samples with and without PEG are shown in Table 1.

Table 1: Gas volumes and gas production indices from 200 mg DM of Hibiscus rosa siensis foliage (ml)
	Incubation time (hour)						Indices
	3	10	24	48	72	96	a	b	C
HF	4.44	20.9	40.4	46.5	48.2	48.4	-7.07	55.6	0.074
HF+PEG	4.13	20.7	40.5	46.6	48.2	48.5	-7.58	56.2	0.074

There were no significant differences in gas volume and gas production indices between samples with and without PEG. This means that the tannin content in HF did not affect gas production and the fermentation rate in the in vitro experiment.

Experiment 1: Effect of Hibiscus rosa siensis silage levels in the diets on feed intake, digestibility and N-NH₃ content in the rumen fluid of goats

Data on the composition of the silage and the grass are in Table 2. The pH of 4.5 in the silage indicates a satisfactory fermentation

Table 2: Chemical composition of the Hibiscus silage and the grass in experiment 1 (% in DM except for DM which is % as fresh matter)
	DM	OM	CP	Ash	pH
Hibiscus silage	36.2	81.2	19.9	18.8	4.45
Native grass	20.1	82.4	11.6	17.6	-

DM intake increased linearly as the proportion of hibiscus silage in the diet increased up to 36% of the diet DM (Table 3; Figure 1). Intake of grass was not affected thus the silage had an 'additive' effect on total DM intake.

Figure 1: Relative intakes of grass and Hibiscus silage by goats fed different levels of the silage

Diet digestibility increased as the proportion of Hibiscus silage in the diet increased (Table 3; Figure 2). It can be predicted from the regression equation that a diet with 100% hibiscus silage would have a DM digestibility of 86.3%.

Figure 2: Effect of level of Hibiscus silage on DM digestibility

Table 4: Mean values for effect of offer levels of Hibiscus silage on the digestibility (%) of DM, OM and CP by goats
	Diets				SEM	P
	HS0	HS400	HS600	HS800	SEM	P
DM	70.9^a	73.5^ab	76.8^b	77.2^b	0.6	0.012
OM	74.3^a	77.0^ab	80.4^b	80.3^b	0.6	0.012
CP	73.1^a	78.3^ab	80.6^ab	81.7^b	1.2	0.036
^abcdMeans within rows without common letter are different at P<0.005

There were no effects of increasing levels of hibiscus silage on rumen pH or ammonia concentration ((Table 5). The latter appeared to be very high on both the control and Hibiscus diets.

Table 5: Mean values for effect of offer levels of Hibiscus silage on rumen ammonia and pH
	Diets				SEM	P
	HS0	HS400	HS600	HS800	SEM	P
pH	6.67	6.74	6.66	6.71	0.02	0.197
N- NH₃(mg/litre)	302	394	405	317	58.9	0.620

Experiment 2: Effect of Hibiscus rosa siensis silage levels in the diets on feed intake, digestibility and N-retention in sheep.

Crude fibre levels were almost twice as high in the elephant grass as in the Hibiscus silage, the latter also having a higher content of crude protein and of ether extract (Table 6). In this experiment, the digestibility values were calculated by the "difference" method (see Materials and Methods for the calculation), which assumes there is no interaction between the two diet ingredients. According to this procedure the DM digestibility was only 69.8% whereas when calculated by regression in Experiment 1, the value was estimated to be much higher (86.3%). The latter value would appear to be the more appropriate one.

Table 6: Mean values for chemical composition of feeds and digestibility coefficients
	DM	OM	CP	CF	EE
Composition, % in DM (except for DM which is on fresh basis)
Hibiscus silage	29.2	89.8	21.1	17.0	5.05
Elephant grass	12.9	88.4	15.2	30.6	2.51
Digestibility coefficients, %
Hibiscus silage	69.8	73.1	84.4
Elephant grass	54.8	58.9	65.3

The effects on feed intake of the sheep (Table 7; Figure 3) and on digestibility (Table 8; Figure 4) by offering increasing level of Hibiscus silage was similar to that observed with goats in Experiment 1.

Table 7. Mean values for effect of offer level of Hibiscus silage on feed intake by sheep
	Diets					SEM	Prob.
	HS0	HS400	HS600	HS800	HS1000	SEM	Prob.
Percentage of HS in diets (%)	0.0	18.7	26.4	34.8	39.6	0.56	0.001
Protein content (% DM)	15.2	16.3	16.8	17.3	17.5	0.03	0.001
Feed DM intake (% of LW)	2.9^a	3.1^ab	3.3^b	3.3^b	3.5^b	0.09	0.002
^abcdMeans within rows without common letter are different at P<0.005

Figure 3: Relative intakes of Elephant grass and Hibiscus silage by sheep fed different levels of the silage

Table 8. Mean values for effect of offer level of Hibiscus silage on digestibility coefficients (%) for DM, OM, and CP by sheep given basal diet of Elephant grass
	Diets					SEM	Prob.
	HS0	HS400	HS600	HS800	HS1000	SEM	Prob.
DM	54.8^a	60.1^b	62.1^bc	63.1^bc	65.1^c	0.97	0.001
OM	59.0^a	63.4^b	65.2^bc	66.2^bc	68.3^c	0.89	0.001
CP	65.3^a	70.6^b	70.1^b	72.1^b	73.9^b	0.83	0.001
^abcdMeans within rows without common letter are different at P<0.005

When the regression equation in Figure 4 is used to predict the digestibility of the Hibiscus silage (eg: when x = 100), the estimated value is 80.1%, which is not so different from the value calculated for Hibiscus silage fed to goats (86.3%) using the regression in Figure 2.

Figure 4: Effect of level of Hibiscus silage on DM digestibility in sheep

The data on N balance of the sheep in Table 9 indicate that almost all the additional nitrogen consumed (an increase of 50% from the diet without Hibiscus silage to the diet containing 40% of the silage) was retained as there were no significant increases in faecal or urine N (Table 9). There was a curvilinear relationship (R²= 0.995)between the proportion of Hibiscus silage in the diet and the retention of nitrogen (Figure 5).

Table 9. Mean values for effect of offer level of Hibiscus silage on N balance in sheep given basal diet of Elephant grass
	Diets					SEM	Prob.
	HS0	HS400	HS600	HS800	HS1000	SEM	Prob.
N balance, g/day
Intake	14.2	17.2	18.6	19.3	21.6	0.35	0.001
Feaces	4.8	4.9	5.6	5.3	5.5	0.21	0.065
Urinary	7.9	7.3	6.8	7.0	8.0	0.54	0.440
Retention	1.5^a	5.0^b	6.3^bc	7.0^bc	8.0^c	0.60	0.001
Retention as % of intake	8.3^a	27.4^b	35.4^b	32.3^b	36.9^b	3.19	0.001
^abdMeans within rows without common letter are different at P<0.005

Figure 5: Effect of level of Hibiscus silage on N retention in sheep

Conclusions

Hibiscus rosa siensis foliage can be ensiled satisfactorily with addition of 5% molasses(W/W).
Goats and sheep fed a basal diet of native grass or elephant grass responded with a linear increase in voluntary intake and DM digestibility as the offer level of Hibiscus silage increased up to 40% of the diet DM.
There was a curvilinear increase in N retention with increasing level of Hibiscus silage in sheep fed a basal diet of Elephant grass

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