Effects of substituting dolichos bean meal with soya bean meal on the performance of broiler chicken

Effects of substituting dolichos bean meal with soya bean meal on the performance of broiler chicken

Department of Animal Science and Production, Sokoine University of Agriculture, P.O.Box 3004, Chuo Kikuu, Morogoro, TANZANIA

Two hundred Cobb broiler chicken one day-old were randomly allocated to five rations containing levels of dolichos beans (Lablab purpureus) meal at 0, 5, 15, 20 and 25 percent and soya bean (Glycine max) meal at 25, 20, 10, 5 and 0 percent. Feed intake, feed utilization efficiency, growth and mortality rates were determined from 2 to 8 weeks at which time the birds were slaughtered, and dressing percentages and organ weights were determined.

As the level of dolichos bean meal increased there was a decrease in crude protein and an increase in crude fibre in the diets, but the changes were not significant (P > 0.05). Weight gain was highest (28.6 g/day) for the ration containing 25 percent soya bean meal and lowest (26.6 g/day) for the diet containing 25 percent dolichos bean meal. Feed intake was highest for the ration containing 25 percent dolichos bean meal but there was no significant difference (P > 0.05) between the treatments. Although the mortality rate was highest (16%) in the diet containing 25 percent dolichos bean meal, the beans were well accepted by the birds, and the protein appeared to be well utilised, with a feed:gain ratio of 3.02. This value was only slightly poorer (P > 0.05) than that recorded for the diet containing 25 percent soya bean meal (2.78).

The role of legumes, both as forage and seeds, as protein supplements in livestock feeding has been well reviewed by Tothill (1986). A number of legumes are now available for use in the tropical and sub-tropical areas. However, so far the research has concentrated mainly on improved exotic species while the abundant indigenous legumes species remain underexplored.

One such legume which is widely grown in Africa is dolichos bean (Lablab purpureus) locally named "fiwi" in Tanzania. The bean can be used as seeds for human and livestock consumption (Pulsegrave 1968; Skerman 1977) and as forage for livestock (Henderiksen and Myles 1980; Kiflewahid 1986). In Tanzania the dolichos bean is 60-70 percent cheaper than soya bean. Although the bean is used for human consumption it is not well liked. Thus the bean is readily available for incorporation in livestock diets.

Unfortunately there have been only limited studies on the use of seeds as livestock feed. Therefore the objective of the present study was to determine the nutritive value of dolichos bean when substituted for soya bean in broiler chicken rations.

Five diets containing various levels of dolichos bean meal were prepared (Table 1). The diets were formulated to be iso-nitrogenous and iso-caloric at about 18% crude protein and 2800 kcal ME/kg of diet. Maize meal and maize bran were the main energy sources, while the protein sources were dolichos bean meal, soya bean meal and fish meal.

Table 1: Ingredient and chemical composition (%) of diets containing dolichos and soya bean meals

Ingredients	C	D5	D15	D20	D25

Maize meal	48.0	53.2	52.7	49.6	49.4
Maize bran	12.9	4.8	2.7	5.4	2.6
Cotton seed cake	9.2	11.6	8.7	13.1	15.6
Soya bean meal	25	20	15	5	0.0
Dolichos bean meal	0.0	5	15	20	25
Fish meal	2.5	3.0	3.5	4.5	5.0
Limestone	2.0	2.0	2.0	2.0	2.0
Vitamin trace mineral premix	0.1	0.1	0.1	0.1	0.1
Salt	0.3	0.3	0.3	0.3	0.3

Nutrient content (% DM):
Dry matter	92.6	93.7	92.6	93.8	92.4
Crude protein	18.9	18.7	18.5	18.3	18.2
Crude fibre	7.2	7.5	7.6	7.8	7.9
Ether extract	5.9	5.6	5.5	5.4	5.3
Ash	6.3	5.9	5.8	6.2	6.0
Calcium *	1.56	1.57	1.59	1.59	1.60
Phosphorus * (available)	0.63	0.65	0.66	0.65	0.67
Methionine*	0.62	0.61	0.61	0.61	0.60

The vitamin - trace mineral mix supplied per kg of diet: Vitamin A, 10,000 IU; D3, 2,000 IU; E, 5 IU; K, 2.24 mg, riboflavin, 55 mg; pantothenic acid, 10 mg; nicotinic acid, 25 mg; choline, 350 mg; folic acid, 1 mg; methionine, 450 mg; Mn 56 mg; I, 1 mg; Fe, 20 mg; Cu 10 mg; An, 50 mg; Co, 1.25 mg.
* Calculated

The dolichos beans and soya beans were locally purchased and processed to remove trypsin inhibitors by the following method. The beans were cracked into two halves in a grain mill and submerged in cold water for 20 h with occasional stiring. The water was subsequently decanted, fresh water added and the mixture was brought to boiling point at 100ºC for 30 minute. The beans were sifted from the water, allowed to cool, sundried and ground to pass through a 1 mm sieve. Representative samples were taken and stored at -20ºC for future analysis.

Two hundred Cobb broiler chicken one day old were wing-banded and randomly distributed into 5 groups of 40 birds which were placed in 2 replicates of 20 birds each. The birds received the full complement of routine vaccinations and were fed and watered ad libitum. They were weighed initially and every two weeks, at which times representative samples of the diets were taken and stored at -20ºC Weekly feed intakes and mortality were recorded. At the end of the trial, the birds were weighed and ten from each replicate were randomly selected, killed and dressed. Dressing consisted of evisceration, with only the kidney and lungs left in the carcass. The shanks were removed at the tibia-tarsal joint, and the head cut off at the first cervical vertebrate joint. The carcass weight as well as weight of the pancreas, spleen, liver and heart were recorded.

Feed intake, feed utilization efficiency, growth and mortality rates were determined from 2 to 8 weeks at which time the birds were slaughtered, and dressing percentages and organ weights were determined.

The samples of the experimental diets were composited, sub-sampled and together with the sub-samples of processed beans were analyzed for dry matter, crude protein, ether extract and ash according to the AOAC (1980) procedures.

The data were analyzed as a completely randomized design using the replicate of 20 birds as the experimental unit. Turkey's procedure was used to separate means differing significantly, as outlined by Steel and Torrie (1960).

The chemical composition of the main ingredients used to compound the experimental rations are shown in Table 2. The results show that the crude protein content in soya bean is 12 percent units higher than that in dolichos beans. The dolichos beans had more than twice the content of crude fibre than soya bean. Ether extract is also much higher in soya bean than in dolichos beans. The differences in the chemical composition between dolichos and soya beans are also reflected in the chemical composition of the ration containing different proportions of the two types of beans (Table 1). The results in Table 1 show that whereas the dry matter and ash contents of the rations did not seem to be much influenced by the levels of substitution of dolichos beans for soya beans, the crude protein content in the diets was observed to decrease as the levels of inclusion of dolichos beans increased. The same trend was observed, though to a less pronounced extent, with respect to the ether extract content of the rations. Crude fibre increased with increasing level of dolichos bean meal in the rations, but the increase among rations with respect to this component was very small.

Table 2: Chemical composition of the main ration ingredients

	Dry matter	Crude protein	Crude fibre	Ether extract	Ash	Nitrogen free-extractives

Maize meal	90.0	9.1	2.4	3.3	1.7	73.4
Maize bran	91.6	10.2	5.9	11.6	4.2	59.6
Cotton seed cake	95.6	33.9	13.3	4.6	6.3	50.2
Soya bean	95.0	34.7	4.0	13.2	4.6	38.5
Dolichos beans	91.2	22.7	9.9	2.3	4.5	51.8
Fish meal	98.4	47.6	1.5	10.9	23.4	15.0

Table 3: Performance of broilers fed on the experimental diets

Ration	Weight gain (g/day)	Feed intake (g/day)	Feed/gain	Dressing

C	28.6	77.8	2.78	70.5
D5	27.5	75.9	2.76	68.3
D15	26.8	76.9	2.87	67.5
D20	27.4	75.9	2.77	66.7
D25	26.6	80.3	3.02	66.1

SE*	±1.17	±0.93	±0.13	±1.3

The performance data of the birds are summarized in Table 3. Feed intake, weight gains and efficiency of feed utilization were not significantly different (P > 0.05) among the treatments. This suggests that the diets containing dolichos beans were well accepted by the birds. Therefore dolichos beans can partially or completely replace soya bean which is three times more expensive. Smith et al (1984) have reported total replacement of soya bean by use of winged bean (Phosphocarpus tetragonolobus).

The relative organ weights and mortality of the experimental birds has been summarised in Table 4. The organ weights were observed to increase with the increasing level of dolichos bean in the diet. However the increase in organ weights were very small and insignificant (P>0.05) between treatments. Organ weights particularly the pancreas and the spleen, are used as an index of the effectiveness of the processing method to destroy trypsin inhibitors (Smith et al 1984). Castillo et al (1980) suggested that soaking of the beans in water for at least 10 hours, followed by boiling for 30 minutes, completely destroys any trypsin activity present in the beans.

Table 4: Relative organ weights and mortality of broilers fed on the experimental diets

Ration	Pancreas	Liver	Heart	Spleen	Mortality (%)
	------ (% of carcass weight) -------

C	0.24	2.85	0.51	0.13	-
D5	0.25	2.91	0.53	0.14	1
D15	0.26	2.93	0.55	0.15	3
D20	0.26	2.97	0.60	0.16	5
D25	0.27	3.21	0.62	0.19	16

SE	±0.02	±0.18	±0.03	±0.02	-

Unfortunately heat-labile trypsin inhibitors are not the only toxic factors in the beans. Other factors identified include haemagglutonating activity, cyanide production, amylase inhibition, and urease activity (Ekpenyong and Borchers 1981). Perhaps some of these factors were not completely inactivated by the processing method and were responsible for the high mortality rate observed in the birds fed the diet containing 25 percent dolichos bean meal.

In conclusion, the dolichos bean, when properly processed to destroy trypsin inhibitors and other toxic factors can be used to partially or completely replace soya bean. Dolichos bean is locally grown and has a low acceptance in human nutrition. Hence it is readily available for incorporation in livestock diets.

This study was partly funded by the Morogoro Regional Cooperative Union (MRCU, 1984) and the Swedish Cooperative Union (Lantmannen).

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