| 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.
General
Mulberry (Morus
alba) leaves were obtained from a plantation on the
Ecological Farm of the
Table
1. Characteristics of the mulberry leaves
(per cent on dry basis) |
||
Analysis |
Mulberry leaves |
|
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 1A
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 |
||||
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.
Treatment
means were compared by conventional analysis of variance, and when a significant
(P<0.05) difference was found,
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.
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 |
||||||
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 |
99.8a |
96.7a |
94.5a |
82.6b |
6.6** |
93.4 |
93.4 |
4.0 |
**
P<0.01 |
||||||||
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, % |
52.2a |
36.5b |
33.6bc |
27.3c |
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 |
226a |
360ab |
410b |
504b |
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 |
||||||||
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 |
55.5a |
54.8a |
61.2a |
80.5b |
10.2 |
59.4 |
63.6 |
5.7 |
*
P<0.05 |
||||||||
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 |
|
Fresh |
Sun dried |
||
Offer |
40.0 |
40.0 |
- |
Intake |
38.2 |
36.2 |
2.4 |
Intake, % of offer |
95.6 |
||