Livestock Research for Rural Development 15 (1) 2003

Citation of this paper

Mulberry (Morus alba) leaves as protein source for young pigs fed rice-based diets: Digestibility studies

Chiv Phiny, T R Preston and J Ly

University of Tropical Agriculture Foundation
Chamcar Daung, PO Box 2423, Phnom Penh, Cambodia
julioly@utafoundation.org; regpreston@utafoundation.org

Abstract

Two experiments were conducted to study the effect of the inclusion of mulberry (Morus alba) leaves in diets for pigs on digestibility indices and N balance.

In experiment 1, a double 4x4 Latin square design in a 2x4 factorial arrangement was used to study the effect of graded levels of mulberry leaf meal (0, 15, 30 and 50% on a dry basis, respectively) in diets based on rice products on the N balance of eight young castrate male Mong Cai or Large White pigs with a mean weight of 14.2 kg. Mulberry leaf meal (MLM) contained DM 30.4 % and in the dry matter: ash 16.9, crude fibre 20.1 and crude protein (Nx6.25) 25.4%, respectively. Feed intake was calculated to be 50 g DM/kg body weight.

Although not significant, DM and organic matter digestibility appeared to increase with increasing levels of dietary MLM. Organic matter was significantly (P<0.05) better digested in Large White than in Mong Cai pigs. N balance indices improved with the inclusion of MLM in the diet, and this effect was significant for N retention (P<0.05) when expressed as proportion of N digested. Mong Cai pigs appeared to have lower N digestion and retention as compared to the Large White.

In experiment 2, six young Mong Cai x Large White castrate male pigs, weighing on average15 kg, were allocated according to a balanced change over design, to two diets where mulberry leaves, either in milled, sun-dried or chopped, fresh, contributed about 45% of the total daily N intake in iso-nitrogenous diets (Nx6.25, 13.7% on a dry basis).

There were no significant effects of treatment on DM, organic matter and N digestibility but dry leaves were associated with slightly lower digestibility values. N balance tended to be better in pigs fed fresh mulberry leaves compared to mulberry leaf meal.

It can be concluded that in rice-based diets for , it is possible to use mulberry leaves as the main protein source.

Key words: Digestibility, leaves, mulberry, pigs, protein

Introduction

Although mulberry trees have been domesticated for many centuries for feeding silkworms (Tingzing et al 1988), very little is known about their nutritive value for non-ruminant animals (see Benavides 1999; Sánchez 1999). This appears to hold true, since from one of the first modern trials conducted to evaluate digestion in mammals as compared to that of silkworms (Maymone et al 1959), to one of the more recent and detailed investigations (Yao et al 2000), the main focus of the studies has been to evaluate mulberry leaves for sheep and cattle. In the particular case of the pig species, very little is known about the nutritive potential and feeding value of mulberry leaves, except for some few reports relating to the subject (Trigueros and Villalta 1997; Ly et al 2001).

Mulberry trees have been used in Cambodia as the substrate for silk worms, but these activities have been developed only on a small scale (Delvert 1961) and, besides, there is no available information concerning the potential value of mulberry leaves as a protein source for animal production.

In this report two approaches to determining the nutritive value of mulberry leaves for pigs have been considered as the main objectives of the study.

Materials and Methods

General

Mulberry (Morus alba) leaves were obtained from a plantation on the Ecological Farm of the University of Tropical Agriculture at Chamcar Daung that was periodically harvested (every two months). The mulberry leaves and petioles were used as fresh material or after being sun-dried. In each case the leaves were either chopped or ground. The mulberry cultivar was of an unknown variety. Some characteristics of the mulberry leaves are shown in Table 1.

Table 1. Characteristics of the mulberry leaves (per cent on dry basis)
Analysis	Mulberry leaves
Analysis	Fresh	Sun dried
Dry matter	26.07	89.68
Ash	17.18	18.50
Organic matter	82.82	81.50
Crude fibre	17.20	20.12
N x 6.25	21.56	18.50
DM solubility, %	40.42	30.33
Water holding capacity, g water/g DM^#	6.15	6.45
^# See text

Two experiments were conducted to study the effect of the inclusion of mulberry leaves i on the nutritive value of rice-based diets fed to growing pigs.

Experiment 1

A double 4x4 Latin square design in a 2x4 factorial arrangement was used to study the effect of including graded levels of mulberry leaf meal replacing rice bran and fish meal in diets based on broken rice (Table 2). Eight young castrate male Mong Cai or Large White pigs weighing on average 14.2 kg were distributed at random into four treatments consisting of four diets containing different levels of mulberry leaves. Mulberry leaves were sun-dried, then ground and mixed with the other components of the diets.

Table 2. Ingredient and chemical composition of the diets
	Mulberry leaf meal, %
	0	15	30	50
Ingredients, % on dry basis
Broken rice	49.45	49.45	49.45	49.45
Rice bran	17.57	12.30	7.03	-
Fish meal	32.43	22.70	12.97	-
Mulberry leaf meal	-	15.00	30.00	50.00
NaCl	0.50	0.50	0.50	0.50
Vitamins and minerals^#	0.05	0.05	0.05	0.05
Analysis, % on dry basis (except for dry matter which is on air-dry basis))
Dry matter	89.67	89.57	89.45	89.81
Ash	12.59	11.44	8.82	7.11
Organic matter	87.41	88.56	91.18	92.89
Crude fibre	5.09	6.58	8.08	10.06
Nx6.25	17.19	16.77	16.34	15.78
WHC, g water/g DM	0.50	1.32	2.14	3.23
^# According to NRC (1998) recommendations

The pigs were housed in metabolism cages (Chiev Phiny and Rodríguez 2001) in an open house. The adaptation period was five days, followed by another five days for total faeces and urine collection. Feed offered was fixed at 50 g DM/kg body weight. Feed ingredients, feed refusals and faeces were assayed for DM content by the method of Undersander et al (1993) in which samples are exposed to microwave radiation until attaining a constant weight. The ash and N content of the samples, and of the urine, was determined following AOAC (1990) procedures.

Treatment means were compared by conventional analysis of variance, and when a significant (P<0.05) difference was found, Duncan’s multiple range test was used (Steel and Torrie 1980). A general linear model was employed through the Minitab software (Ryan et al 1985).

Experiment 2

Six young Mong Cai x Large White castrate male pigs weighing on average 15 kg were allocated, according to a balanced two period change-over design (Gill 1978; Gill and Magee 1976), to two diets based on rice and wheat products (Table 3) where mulberry leaves, either sun-dried and then milled, or fresh and chopped, contributed 45% of the total daily N intake in iso-nitrogenous diets.

Table 3. Ingredient and chemical composition of the diets
	Mulberry leaves
	Fresh	Sun dried
Ingredients, % on dry basis
Wheat bran	35.0	35.0
Broken rice	39.8	34.8
Chopped mulberry leaves	25.0	-
Mulberry leaf meal	-	30.0
Vitamins and minerals^#	0.2	0.2
Analysis, % on dry basis
Dry matter	87.84	88.37
Ash	5.38	6.75
Organic matter	94.62	93.25
Crude fibre	11.30	13.04
Nx6.25	13.70	13.70
WHC, g water/g DM	4.05	4.60
^# According to NRC (1998) recommendations

The same procedures as described in Experiment 1 were used for animal housing, feeding and collection of excretion outputs. In the case of the treatment with fresh mulberry leaves, the amount of foliage needed was harvested every day, and then offered to the animals after chopping and before giving the supplement containing the dry components of the diet. Feed offered was 40 g DM/kg of body weight.

The same analytical methods as in Experiment 1 were used for the determination of the amounts feed offered and refusals, and faeces and urine ouputs. Representative samples of fresh and dried mulberry leaves were analysed for DM solubility as described by Ly and Preston (2001) and for water holding capacity (WHC) following a method detailed elsewhere (Ly et al 2002) and based on that of Tsaras et al (1998). The procedure consisted of filtration of samples after being suspended in water for16 hours. The fresh samples of leaves were first blended for five minutes prior to mixing with water, and the dried leaves were treated with water after sun-drying. Other determinations consisted of faecal pH measurements using a glass electrode connected to a digital precision pH meter.

The recommendations of Gill (1978) and Gill and Magee (1976) were followed for carrying out the analysis of variance. Standard procedures were applied as in Experiment 1, using Minitab software.

Results and Discussion

Experiment 1

Pigs offered the highest proportion of mulberry leaf meal (50%) in the diet had significant refusals (Table 4) (P<0.01) and voluntary feed intake was only just over 80% of the amount offered, whereas feed refusals in rations containing up to 30% of mulberry leaf meal were minimal. There was neither a significant effect of breed nor any interaction between the main effects of breed and diet on feed intake.

Table 4. Feed intake of young pigs fed mulberry leaf meal
Ration, g DM/kg W	Mulberry leaf meal, %					Genotype
Ration, g DM/kg W	0	15	30	50	SEM	Mong Cai	Large White	SEM
Offer	50.0	50.0	50.0	50.0	-	50.0	50.0	-
Intake	49.9	48.4	47.3	41.3	3.3	46.7	46.7	2.0
Intake, % of offer	99.8^a	96.7^a	94.5^a	82.6^b	6.6**	93.4	93.4	4.0
^* P<0.01; ^ab Means without common superscripts in the same row differ at (P<0.05)*

In spite of the fact that diets varying in capacity to hold water (WHC) were offered, the animals only refused to consume the entire ration when mulberry leaf meal accounted for 50% of the dietary formula. The WHC has been suggested to be closely linked to the ability of pigs to voluntarily consume bulky feeds (Kyriazakis and Emmans 1995; Tsaras et al 1998). According to the current study this interdependence could not occur in a linear manner, perhaps due to variations in other feed characteristics, such as nutrient digestibility.

Faecal DM concentration was negatively influenced (P<0.01) by the inclusion of mulberry leaf meal in the ration (Table 5). A considerable variability was observed in the animals’ response in faecal ouput of fresh material and water when mulberry leaf meal accounted for 30 or 50% of the diet. As a consequence, the analysis of variance did not reveal any differences amongst treatments. However, increasing levels of mulberry leaves in the diet resulted in a significant (P<0.05) increase in faecal water output and the same trend was found (P<0.10) for fresh material output (Figure 1).

Figure 1: Effect of increasing levels of mulberry leaf in the diet on
fresh faeces output in growing pigs

An increase in faecal fresh material and water output has been associated with an increase in the fibrous fraction of the diet, as a result of its bulking characteristics (Bach Knudsen and Hansen 1991). Therefore, it has been assumed that WHC could be used to predict increases in faecal output in pigs, since it has been claimed that WHC is a physico-chemical property of cell walls with direct physiological implications in the gastrointestinal tract of pigs (Leterme et al 1998). In this connection, more fresh material and water tended to be excreted with a constant faecal DM concentration from the large intestine in Mong Cai as compared to Large White pigs.

Table 5. Nutrient digestibility of diets containing mulberry leaf meal in young pigs
	Mulberry leaf meal, %					Genotype
	0	15	30	50	SEM	Mong Cai	Large White	SEM
Faecal DM, %	52.2^a	36.5^b	33.6^bc	27.3^c	3.09^**	36.3	40.0	3.38
Faecal output, g/kg DM intake
Fresh material	479	564	618	680	139⁺	620	500	73
DM	253	204	208	176	44	225	201	23
Water	226^a	360^ab	410^b	504^b	122*	395	299	71
Digestibility, %
Dry matter	75.0	79.5	79.3	82.3	4.3	77.5	79.9	2.2
Organic matter	82.5	84.2	82.8	85.1	3.9	81.7	85.5	1.8*
⁺ P<0.10; ^P<0.05; ^** P<0.01; ^abc Means in the same row without common superscripts differ significantly (P<0.05)*

Dry matter and organic matter digestibility tended to increase with increasing levels of dietary mulberry leaves (Table 5) and at the same time both digestive indices appeared to be negatively influenced by the ash content of the diets (see Table 2). There were no significant differences between genotypes for DM digestibility, but Mong Cai pigs had a digestibility of organic matter (P<0.05) that was almost four percentage units lower than for the Large White pigs.

There was no significant treatment influence on N digestibility or N retention (Table 6). However, N retention appeared to be improved with increasing levels of mulberry leaf meal in the diet, either expressed as a percentage of N ingested or N digested. In fact, the diet where mulberry leaf meal was the only protein source had the highest N balance, when N retention was expressed as percentage of the digested N. Ly et al (2001) also found that Mong Cai pigs had a high retention of N when mulberry leaf meal was 30% of the diet.

Although not significant, Mong Cai pigs tended to have a lower N digestibility and N retention than Large White pigs. These results confirm the trend towards a lower digestion of N compounds by Mong Cai pigs previously observed by Nguyen Thi Thuy and Ly (2002).

Table 6. Effect of mulberry leaf meal on N balance in young pigs
	Mulberry leaf meal, %					Genotype
	0	15	30	50	SEM	Mong Cai	Large White	SEM
N digestibility, %	73.5	72.6	69.3	71.1	6.1	68.4	74.9	3.9
N retention
In g/day	8.10	7.55	8.05	9.95	3.34	7.14	9.68	1.58
As % of intake	41.0	39.8	42.9	54.1	9.8	40.9	48.0	5.0
As % of digested	55.5^a	54.8^a	61.2^a	80.5^b	10.2	59.4	63.6	5.7
* P<0.05; ^ab Means in the same row without common superscripts differ (P<0.05)

Experiment 2

Even though the amount of food offered was reduced from 50 g DM/kg LW (Experiment 1) to 40 g DM/kg LW, feed refusals were recorded for diets containing both fresh and sun-dried leaves (Table 7). In fact, feed intake was somewhat lower than for animals given diets containing 30% of mulberry leaf meal (47.3 g DM/kg W) in Experiment 1. It is probable that the introduction of wheat bran into the diet had an additional negative influence on the voluntary feed intake. The WHC of rice bran used in Experiment 1 (2.85 ± 0.38 g water/g DM), was considerably lower than that of the wheat bran used in Experiment 2 (7.59 ± 0.13 g water/g DM), and as a result the WHC of the diets used in Experiment 2 (4.13 and 4.60 g water/g DM) were higher than those of the diets used in Experiment 1 (0.50 to 3.23 g water/g DM, see Table 2). Tsaras et al (1998) also found high WHC values for the wheat bran used in their studies.

It appeared that pigs preferred fresh to sun-dried mulberry leaves, but this preference was not significant.

Table 7. Effect of sun-drying of mulberry leaves on feed intake in young pigs
Ration, g DM/kg W	Mulberry leaves		SEM
Ration, g DM/kg W	Fresh	Sun dried	SEM
Offer	40.0	40.0	-
Intake	38.2	36.2	2.4
Intake, % of offer	95.6	90.5	5.8

Faecal ouput of fresh material and water was similar for pigs fed either dry or fresh leaves of mulberry (Table 8), and these indices were somewhat lower than the same parameters for pigs fed diets based on rice products with 30% of mulberry leaf meal in Experiment 1. Nevertheless, a significant (P<0.01) exponential interdependence was found between fresh faecal output and WHC when data from both experiments were pooled (Figure 2). The relationship between the crude fibre content of the diets and fresh faeces output was relatively weak (R² = 0.54; P< 0.10), thus supporting the theory that certain physico-chemical properties of fibrous material in the diets are responsible for the bulkiness of faeces in pigs.

Figure 2. Influence of water holding capacity of the diet on fresh faeces output in pigs
fed mulberry leaves as protein supplement

Digestibility indices in pigs fed mulberry leaves were relatively high. There were no significant effects of treatment on DM and organic matter digestibility, although dry leaves tended to be associated with slightly lower digestibility indices (overall means, 83.2 and 84.5%, respectively). In fact, dry leaves showed a lower DM solubility in water than fresh leaves, according to the wash values obtained in this study (see Table 1), thus suggesting a low in vivo, pre-caecal DM digestibility.

Table 8. Effect of sun-drying on digestibility indices in young crossbred pigs
	Mulberry leaves		SEM
	Fresh	Sun dried	SEM
Faecal indices
pH	5.85	5.95	0.46
Dry matter, %	26.4	29.1	1.73
Faecal output, g/kg DM intake
Fresh material	618	617	85
DM	161	176	24
Water	457	441	66
Digestibility, %
Dry matter	83.9	82.4	1.7
Organic matter	85.1	83.9	1.7

N balance tended to higher in pigs fed fresh mulberry leaves as compared to mulberry leaf meal (Table 9), but the difference was not significant (P<0.30).

Table 9. Balance of N in young pigs fed mulberry leaves
(Experiment 2)	Mulberry leaves		SEM
(Experiment 2)	Fresh	Sun dry	SEM
N digestibility, %	75.0	74.7	3.9
N balance, g/day
Intake	13.21	13.49	2.39
Faecal output	3.30	3.41	0.77
Digested	9.91	10.08	1.95
Urine output	2.45	2.85	0.55
Total output	5.75	6.26	1.08
N Retention
g/day	7.46	7.23	1.61
% of N intake	56.6	47.4	4.7
% of digested N	75.3	71.7	4.1

According to the results from the present studies, it appears to be possible to replace conventional protein sources by mulberry leaves in diets for growing pigs based on rice products with no deleterious effects on N balance. More investigations are needed to further study the pattern of digestion of mulberry leaves in pigs and to determine the optimal proportion of amino acids in diets for pigs based on rice products and mulberry leaves. In addition, studies to determine the feeding value of mulberry leaves for growing pigs and sows in tropical environments are necessary.

Acknowledgments

The authors gratefully acknowledge the financial support of the MEKARN project (funded by Sida-SAREC) for the present investigation. Thanks are also given to Mr. Keo Saeth and Mr. Son Ron for their technical support in Experiments 1 and 2, respectively. Similarly, the authors express their gratitude to Mr. Pok Samkol for his analytical assistance.

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Mulberry (Morus alba) leaves as protein source for young pigs fed rice-based diets: Digestibility studies

Chiv Phiny, T R Preston and J Ly

University of Tropical Agriculture Foundation Chamcar Daung, PO Box 2423, Phnom Penh, Cambodia julioly@utafoundation.org; regpreston@utafoundation.org

Abstract

Key words: Digestibility, leaves, mulberry, pigs, protein

Introduction

Materials and Methods

General

Experiment 1

Ingredients, % on dry basis

Experiment 2

Ingredients, % on dry basis

Analysis, % on dry basis

Results and Discussion

Experiment 1

Experiment 2

Acknowledgments

References

University of Tropical Agriculture Foundation
Chamcar Daung, PO Box 2423, Phnom Penh, Cambodia
julioly@utafoundation.org; regpreston@utafoundation.org