Livestock Research for Rural Development 15 (11) 2003

Citation of this paper

Evaluation of the potential of Trichanthera gigantea as a source of nutrients for rabbit diets under small-holder production system in Tanzania

S V Sarwatt, G H Laswai and R Ubwe

Department of Animal Science and Production, Sokoine University of Agriculture,
PO Box 3004, Morogoro, Tanzania
svsarwatt@yahoo.com

Abstract

A digestibility trial and a growth performance study were carried out to evaluate the potential of Trichanthera gigantea as a substitute for the conventional protein sources in the diets of growing rabbits. In the digestibility trial, 12 male rabbits were allocated to four dietary treatments in a completely randomised design and repeated twice to give six observations per treatment. Diet 1 was a control formulated to contain conventional ingredients for rabbit diets. Diets 2, 3 and 4 contained 9%, 18% and 27%, respectively of Trichanthera gigantea replacing similar portions of the control diet. A preliminary period of 7 days was followed by similar number of days for collection period. Digestibility of nutrients of each diet was estimated and metabolisable energy predicted. In the growth study, 48 weaned rabbits (24 males and 24 females) were randomly allocated to the four diets in a completely randomised block design. Feed intake, growth performance, feed conversion ratio and slaughter parameters were measured on the animals for a period of 8 weeks.

The crude protein and crude fibre contents of Trichanthera gigantea were 23.9 and 23.8% in dry matter (DM), respectively. The mean values of crude protein and ether extract digestibility decreased significantly (P<0.05) from 83.6 to 74.5% and 91.0 to 76.4%, respectively and that of crude fibre increased from 13.9 to 25.0% with increased levels of Trichanthera gigantea in the diets. Inclusion of Trichanthera gigantea in the diets significantly (P<0.05) increased daily average DM intake from 51.4 to 73.6 g, protein intake from 11.2 to 16.7 g, growth rate from 12.8 to 18.2 g/d and hot carcass weight from 1203 to 1301 g, relative to the control. The average feed conversion ratio was not significantly (P>0.05) influenced by the diets. The differences between sexes for most parameters were not significant (P>0.05).

It was concluded that levels up to 27% of Trichanthera gigantea could be included in the diet of growing rabbits to promote feed intake and growth performance without influencing the feed conversion efficiency. .

Keywords: Digestibility, growth,  intake, rabbits, Trichanthera gigantea,


Introduction

Most rabbit producers in Tanzania operate on a small-scale subsistence level and feed their animals on local feed resources including forages. Although the use of concentrate would have been most desirable, the high price and unavailability of concentrates in terms of quantity and quality make them to have limited use in rabbit production. Forages are good sources of dietary protein, minerals and vitamins for rabbits. One of the advantages of feeding forages to rabbits is that the protein contained in forages is extracted efficiently by rabbits due to multiple passages in the gastrointestinal tract. A number of forage plants, for example Gliricidia sepium, Leucaena leucocephala and Crotalaria ochroleuca have high protein content and have been used to feed rabbits in Tanzania. However, most of these plants have some limitations on the amount to be used as they contain toxic substances, and when fed at high levels to rabbits affect their performance (Laswai et al 2000). A combination of small quantities of several forages could reduce the problem of toxicity and result in a better balanced diet than using a single forage. This calls for the need to evaluate the nutritional potential of different forages for rabbits.

Another potential forage for supplying nutrients to rabbits is Trichanthera gigantea. It is a multipurpose tree originating from Colombia and recently has been introduced to Tanzania. The tree is evergreen and highly nutritious. The crude protein (CP) content of the leaves was estimated to be 22%, and a large proportion of its protein is true protein and has a good balance of amino acids (Nguyen Thi Hong Nhan and Nguyen Van Hon 1999). The plant contains low levels of anti-nutritional factors (Galindo et al 1989; Keir et al 1997; Rosales 1997) and the leaves are highly palatable to animals. The plant is also rich in mineral content (Nguyen Thi Hong Nhan et al 1996; Hess and Dominguez 1998). Growth rates of about 32 g/day have been reported with rabbits fed Trichanthera gigantea leaf meal mixed with concentrates (Rosales 1997).

There is limited information on the feeding value for rabbits of Trichanthera gigantea grown in Tanzania. The present study was therefore conducted to determine the chemical composition of Trichanthera gigantea and the effect of its inclusion in diets on the nutrient digestibility, growth performance, feed conversion efficiency and slaughter characteristics of rabbits.


Materials and methods

A digestibility trial and a growth performance study were carried out with the aim of evaluating the feeding value of diets containing different levels of Trichanthera gigantea to rabbits.

Research site

The study was carried out at Sokoine University of Agriculture (SUA) in Morogoro, Tanzania. The university is located between 6 and 7° S and 37 and 38° E and altitude of 500 to 600 m above see level. The area receives an average annual rainfall of between 600 to 1000 mm and experiences day temperature ranging between 20 to 27° C in the coolest months (April to September) and 30 to 37° C during the hottest months (October to March).

Digestibility trial
Experimental design and treatments

Twelve male rabbits were allocated randomly into four dietary treatments in a completely randomised design. This was repeated with new randomisation of the animals into treatments, forming 6 replications per treatment. Dietary treatment T0 was a control diet formulated to contain (g/kg) 170 sunflower seed cake, 125 cotton seed cake, 630 maize bran, 20 molasses, 30 fish meal, 10 vitamin mineral mix, 10 limestone and 5 salt. Treatments T90, T180 and T270 were formulated to contain 90, 180 and 270 g/kg DM, respectively of Trichanthera gigantea replacing similar weight of the control diet. The four diets were balanced to contain 220g crude protein (CP)/kg.

Experimental animals and their management

The rabbits were crossbred New Zealand White and California White obtained from the Department of Animal Science and Production, Sokoine University of Agriculture (SUA). After birth the kids were left with their mothers for 42 days, after which they were weaned. They were fed on a common rabbit feed used in the unit. The animals were allocated randomly to the four dietary treatments at the age of 118±10 days and mean initial weight of 1.8±0.2 kg, respectively. They were housed in a well-ventilated building and kept in individual cages, which were measuring 57x53x60 cm, with wire mesh sieve and trays to separate faeces and urine.

Source of the feed materials

Trichanthera gigantea leaves were harvested from the plants established within the SUA Farm and air dried under shade for two weeks. The other feed ingredients were purchased from the shops in Morogoro town. All the ingredients were milled separately to pass through a 2mm sieve before mixing them together to form the respective diets. The diets were supplied to the animals in meal form.

Experimental protocol

The experimental protocol included a 7 d collection preceded by a 7 d preliminary period. During the collection period each animal was offered 100 g of the respective diet per day, an allowance established during the preliminary period. The feed was weighed daily into nylon bags and placed into feed hoppers twice a day at 0900h and 1500h. Each morning before feeding, spilt feed was collected from each tray, oven dried and weighed. Feed remaining in the feeders was also weighed after drying. Clean drinking water was provided daily in clean plastic bottles hanging on the cages.

The faeces and urine from each animal were collected and weighed daily at 0800h a.m. The daily fresh faeces were bulked in plastic bags and preserved in a deep freezer. Urine was preserved under acidic medium (6% H2SO4 and 3% CuSO4 mixed together in 1 litre of distilled water) so as to avoid escape of nitrogen and stored in airtight bottles at room temperature. At the end of the experimental period any rabbit fur in the faeces was carefully removed and faeces reweighed. The faeces for each rabbit were thoroughly mixed and 20% of the fresh weight was sampled and stored in a deep freezer for nitrogen determination. The frozen faecal samples were ground using a small blender before nitrogen determination. The other portion of the faeces was oven dried at 60oC for DM determination, ground and stored for subsequent analyses. The total urine collected was stored in a deep freezer for nitrogen determination.

Growth performance study
Experimental design and treatments

A total of 48 growing rabbits (24 males and 24 females) were blocked by sex and allocated randomly into the four dietary treatments used in Experiment 1 in a completely randomised block design.

Feeding and management of experimental animals

The rabbits originated from the similar source as those used in the digestibility trial. They were allocated to the dietary treatments when aged 48±3 days with initial body weight of 606138 g. The rabbits were caged individually in a well-ventilated building. A preliminary period of two weeks was followed by a data-recording period of eight (8) weeks. Feeding of the experimental animals was ad libitum. The amount of feed in excess of requirement for each rabbit was weighted weekly in labelled polythene bags. Small amounts of feed were placed in concrete feeders several times a day for controlling spillage. Each morning before feeding all the spilt feed was collected from the trays, air dried for 24 hours to remove the moisture resulting from drinking water and/or urine, and then bulked till the day of weighing. Feed intake was measured weekly and it was taken as the difference between the total weekly allowance and the remaining feed plus refusal. Clean drinking water was provided ad libitum in concrete containers;  a coccidiostat was put into the water during the first two weeks of the experiment. The animals were weighed weekly in the morning before feeding and watering. Feed was withheld for two hours prior to weighing so as to reduce the effect of gut fill on the live weights. Final weight was recorded at the end of the 8 weeks of the experimental period and weight gain was calculated as the difference between two consecutive weightings.

Slaughter procedure

The experimental animals continued with their respective treatments after the growth study until they weighed 2500 ± 100 g, when eight rabbits (4 males and 4 females) were taken randomly from each dietary treatment and slaughtered. Feed and water were withheld for two hours before the animals were slaughtered. The animals were slaughtered by dislocating the neck and bled by severing carotid arteries and jugular veins with a sharp knife. They were then skinned, the head, feet and non-carcass components removed and the hot carcass weighed.

Chemical and data analysis

The proximate composition of Trichanthera gigantea leaves, feed ingredients used in both control and experimental diets, faeces and urine was determined according to standard methods of AOAC (1990). Metabolisable energy (ME) was calculated according to the equation developed by Jentsch et al. (1963), quoted by Lang (1981) as:

ME = 4.38X1 + 9.37X2 + 4.45X3 + 4.18X4 + 71 kcal/kg

Where, X1, X2, X3 and X4 are the contents of digestible fractions (g/kg) of CP, ether extract (EE), crude fibre (CF) and nitrogen free extractives (NFE), respectively.

Statistical analysis

The results were analysed using the Statistical Analysis System (SAS 1990). Treatment means were compared using the method of Least Square Difference (LSD) according to SAS (1990).


Results

Chemical composition

The chemical composition of feed ingredients and diets is given in Table 1. The CP content of Trichanthera gigantea leaf meal was lower than that of cotton seed cake and sunflower seed cake. The CF content was more or less similar to that of cottonseed meal but lower than that of sunflower seed meal. The experimental diets had similar CP content of 22.23.5%. The CF and ash contents increased, whereas EE content decreased with increasing level of Trichanthera gigantea leaf meal in the diets.

Table 1. Chemical composition of the ingredients and diets used in the experiments

Feed

DM

Component (g/kg DM)

(g/kg)

CP

CF

EE

Ash

NFE

Ingredients

 

 

 

 

 

 

Trichanthera gigantea leaves

789

239

238

25

243

255

Sunflower seed cake

885

293

392

152

44

119

Cotton seed cake

869

426

229

79

55

211

Maize bran

814

141

53

147

45

614

Fish meal

883

518

12

117

332

21

Dietary treatment

 

 

 

 

 

 

T0

879

224

112

145

83

436

T90

877

221

122

129

97

431

T180

873

226

133

89

111

441

T270

874

218

128

75

123

456

Digestibility and nitrogen balance

Digestibility coefficients of DM and organic matter were not significantly influenced by the inclusion level of Trichanthera gigantea leaf meal (Table 2). Digestibility of CP and EE significantly decreased and that of CF significantly increased with increasing inclusion level of Trichanthera gigantea leaf meal in the diets. The mean values of ME significantly (P<0.05) decreased and faecal N excretion increased with increasing level of inclusion of Trichanthera gigantea leaf meal in the diet. The treatment effects on nitrogen retention and efficiency of nitrogen utilisation were not significant (P>0.05).

Table 2. Effect of dietary treatments on nutrient digestibility and nitrogen utilisation by rabbits

Component

Treatment

SEM

T0

T90

T180

T270

Digestibility coefficients (%)

 

DM

72.2

69.9

71.7

72.4

1.8NS

OM

73.8

71.6

73.2

73.4

1.6NS

CP

83.6 a

78.7b

78.0bc

74.5c

1.2***

EE

91.0a

88.3ab

84.9b

76.4c

1.5***

CF

13.9b

19.1ab

25.0a

23.9a

3.3*

Ash

55.2

53.9

59.7

65.2

3.5NS

NFE

78.3

77.8

82.4

86.2

2.5NS

ME (MJ/kg DM)

15.1a

14.2b

13.5bbc

13.0c

0.3***

Nitrogen balance (g/d)

 

 

 

 

Intake

2.42

2.32

2.39

2.44

0.13NS

In faeces

0.40c

0.49bc

0.53ab

0.63a

0.04*

In urine

0.82

0.96

0.74

0.88

0.09NS

Retention

1.20

0.87

1.12

0.94

0.13NS

N-retained/N-intake

0.49

0.37

0.47

0.38

0.05NS

N-retained/N-absorbed

0.59

0.47

0.59

0.51

0.05NS

abcd Values in the same row without superscript letters in common differ  at (P<0.05)
NS  Not significant
*, **, *** Different at P<0.05, P<0.01 and P<0.001, respectively.
SEM  Standard error of the mean difference.

Feed intake, growth performance and slaughter characteristics

The mean differences in the DM intake between rabbits on T90, T180 and T270 were not significant, but were  higher than those on T1. Inclusion of Trichanthera gigantea in the diet led to on average 26 and 44% increase in intake of ME and protein, respectively. The mean final weight and growth rate (GR) of rabbits fed on T90, T180 and T270 were not significantly different, but were higher than those fed on T0. The mean values of feed conversion ratio (FCR) were not significantly different between the dietary treatments, though the value tended to improve slightly in Treatment T90. There was no difference between sexes in all the measured growth parameters.

Table 3. Effects of level of Trichanthera leaf meal and sex on intake of dry matter (DMI), energy (MEI) and protein  (PI) and on growth rate and feed conversion ratio (FCR) by rabbits

Parameter

Trichanthera leaf meal, g/kg

SEM

Sex

SEM

0

90

180

270

M

F

Daily intake                

DM, g

51.4b

70.8a

73.4a

73.6a

2.7***

67.0

67.6

1.9NS

ME, MJ

0.78b

1.01a

0.99a

0.95a

0.04***

0.93

0.93

0.03NS

CP, g

11.3b

15.5a

16.6a

16.7a

0.61***

15.0

15.1

0.4NS

Live weight, g              

Initial

783

771

832

787

 

728

858

 

Final

1682b

2085a

2112a

2007a

87.2**

1968

1975

61.6NS

Daily gain

12.8b

18.8a

18.3a

17.4a

0.96***

17.7

16.0

0.7NS

FCR 

4.0

3.8

4.0

4.2

0.3NS

3.8

4.2

0.2NS

ab Values in the same row without superscript letters in common differ  at (P<0.05)
NS  Not significant
*, **, *** Different at P<0.05, P<0.01 and P<0.001, respectively.
SEM  Standard error of the mean difference

The mean values of slaughter weight and empty body weight were not significantly influenced by either treatment or sexes (Table 4). The mean values of hot carcass weight and dressing percentage were significantly lower for control  animals (T0) than for those fed Trichanthera leaf meal.  The mean proportion of hot carcass as percent of empty body weight was not influenced by the dietary treatments but significantly higher in females than in male rabbits.

Table 4. Effect of level of Trichanthera leaf meal and sex on slaughter weight , empty body weights, hot carcass weight and dressing percentage of rabbits

Component

Treatment

SEM

Sex

SEM

T1

T2

T3

T4

M

F

Slaughter weight, g

2500

2568

2559

2575

38.8NS

2535

2567

27.4NS

Empty body weight, g

2239

2328

2340

2342

40.1NS

2310

2314

28.4NS

Empty body weight as % of slaughter weight

89.5

90.6

91.4

91.0

0.6NS

91.1

90.1

0.4NS

Hot carcass weight, g

1203b

1302 a

1309a

1293 a

26.9 *

1258

1296

19.0NS

Hot carcass weight as % of empty body weight

53.7

55.9

56.0

55.2

   0.6NS

54.4

56.0

0.4*

Dressing percentage, %

  48.1 b

  50.7 a

  51.3 a

  50.2 a

0.7 *

49.6

50.5

    0.5NS

ab Values in the same row without superscript letters in common differ  at (P<0.05)
NS  Not significant
* Different at P<0.05
SEM  Standard error of the mean difference


Discussion

The CP content (239 g/kg) of Trichanthera gigantea was higher than the range of 125 to  217 g/kg reported by Nguyen Thi Duyen et al.(1996), Rosales (1997), Ha (1998), Nguyen Thi Hong Nhan and Nguyen Van Hon (1999) and Ly et al (2001) for the same forage. Also the CF (238 g/kg) in the present study was higher than the range of 138 to 168 g/kg reported by Nguyen Thi Hong Nhan and Nguyen Van Hon (1999) and Ly et al. (2001). The observed discrepancies could be due to the harvest time since mature plants have more cell wall and less cell contents than young plants. The Trichanthera gigantea leaves used in the present study were harvested when the plants were in the vegetative stage. The CP content of the experimental diets (average 220g CP/kg DM) was slightly higher than the value of 200g CP/kg DM recommended for diets of growing rabbits (Lebas 1988). The range of CF contents (112 to 133g CF/kg DM) was within the recommended range of 100 to 150g CF/kg DM for rabbit diets (Lebas 1988).

The observed decrease in the mean values of CP digestibility with increasing levels of Trichanthera gigantea inclusion in the diet is in agreement with the data reported by Maeda (2000) when he used different levels of Morus alba in the rabbit diet. The decrease could be attributed to the low digestibility of CP in Trichanthera gigantea  itself. This decrease was also associated with the significant increase in faecal nitrogen content as levels of Trichanthera gigantea in the diet increased. The similar values for urinary nitrogen between treatments could imply that the protein quality of Trichanthera gigantea matches well with that of sunflower seed cake, hence the protein metabolism was not significantly influenced by its substitution with Trichanthera gigantea. The observed decreased digestibility of EE with increasing levels of Trichanthera gigantea inclusion in the diets could be associated with the observed concomitant decrease in fat content in the diets. These results are in agreement with the results reported by Maeda (2000) and Fernández et al (1994) that digestibility of fat decreases with decreasing levels of fat in the diets. The observed increased digestibility of CF with increasing levels of Trichanthera gigantea leaf meal inclusion in the diets is in agreement with the data of Maeda (2000), who observed higher CF digestibility for diets having leaf meals than for the control diet. This observation could possibly be due to balancing of nutrients in terms of vitamins and minerals from the leaf meals and hence improvement of digestive capacity. The predicted values of ME content of the diets were relatively higher than the recommended optimum value of 11.2 MJ/kg DM by Lebas et al.(1986). Such high values are not expected in diets based on by-products and forages, but could result due to limitations in using prediction equations developed using feeds of different composition from the ones used in the present study. The decrease in ME content with increased levels of Trichanthera gigantea leaf meal in the diet was expected as inclusion of leaf meals in diets tends to lower both the content and digestibility of energy sources, such as ether extract (D'mello 1992).

The range of dry matter intake (51 to 74 g/d) recorded in the present study was lower than the ranges of 86.8 to 93.0 g/d and 140 to 160 g/d recommended for rabbits aged 56 and 112 days, respectively (Lebas et al 1986). The low intake in the present study could be due to high temperature (range of 27 to 35° C) experienced during the experimental period, as temperatures above 30° C are known to lower intake (Lebas et al 1986). The form in which the feeds were offered in the present study could have also depressed feed intake, as rabbits eat more of pelleted than meal feeds (McNitt et al 2000). The observed higher dry matter intake by the animals fed on Trichanthera gigantea leaf meal based diets than the control diet might be attributed to increased palatability due to additional amino acids, minerals and vitamins, which are known to be present in relatively high levels in leaf meals (D'Mello 1992). A similar observation was made when Crotalaria ochroleuca (Laswai et al 2000) and Morus alba (Maeda 2000) were added to the control diet. Trichanthera gigantea leaf meal protein is reported to be balanced in terms of essential amino acids (Rosales 1997), which are known to enhance voluntary feed intake by rabbits (McNitt et al 2000). The increased rate of feed intake with inclusion of Trichanthera gigantea could also be associated with the observed increase in fibre content, as dietary fibre promotes a faster rate of passage through the gastrointestinal tract of a rabbit, which encourages feed intake (Gidenne 1993; Lang et al 1981). In addition, leaf meals have a tendency of reducing dustiness in meal feeds and hence encourage feed intake (Lebas 1988).

The relatively low feed intake and consequently low CP intake could partly account for the observed lower growth performance of the rabbits fed on the control diet (T0) relative to those on the other treatments. These results were unexpected as higher values of digestibility and nitrogen retention were observed with the control diet in Experiment 1.  This discrepancy could be due to the short experimental period and restricted feeding during the digestibility trial, which might have camouflaged the negative effects of the dietary nutrient balance. The control diet (T0) might also have had low levels of non-digestible fibre, which is known to enhance passage rate of digesta, maintain proper gut function and normal health of the rabbits (Lang 1981). There were also some cases of soft droppings from the animals fed on the control diet,  indicating signs of enteritis, which could have influenced feed utilisation and resulted into poor performance (Lang 1981).

The overall mean growth rate (16.8 g/d) observed in the present study was lower than the recorded range of 30 to 40 g/d in growing rabbits (Lebas 1986; McNitt et al 2000). The observed mean weight gain (18.2 g/d) of rabbits fed diets containing Trichanthera gigantea leaf meal was also lower than that of 32 g/d reported by Rosales (1997) in Columbia when Trichanthera gigantea was included in rabbit diets at a level of 30 %.

The average dressing percentage of 50% was within the range of 50 to 60% reported by Fielding and Matheron (1991), Maeda (2000) and McNitt et al (2000) for rabbits.


Conclusion

Inclusion of Trichanthera gigantea leaf meal in the rabbit diets improved feed intake, growth performance and dressing percentage.

It was concluded that up to 270 g/kg of compounded rabbit feeds could be replaced by Trichanthera gigantea leaf meal.


Acknowledgements

The Norwegian Agency for Development and Co-operation (NORAD) is highly acknowledged for financing the research reported in this paper.


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Received 30 July 2003; Accepted 1 September 2003

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