Short communication
A note on a comparison of the feeding value of sweet
potato vines and lucerne meal for broiler chickens
D.J. Farrell
a,b,*, H. Jibril
a, R.A. Perez-Maldonado
b, P.F. Mannion
baSchool of Land and Food, The University of Queensland, St Lucia, Qld 4072, Australia bQueensland Poultry Research and Development Centre, Alexandra Hills, Qld 4161, Australia
Received 17 December 1998; received in revised form 20 July 1999; accepted 17 February 2000
Abstract
The chemical composition of sun-dried sweet potato vines (SPV) and lucerne meal showed high levels (g/kg DM) of neutral detergent ®bre, ash and protein of 364 and 352, 178 and 100, and 191 and 182, respectively. Amino acid analysis showed modest levels of lysine, threonine and the sulfur amino acids in both meals but concentrations of these amino acids were generally higher in lucerne meal than SPV meal despite similar crude protein values. Mineral analysis showed a useful amount of Ca (10 g/kg) in both meals. When SPV meal replaced lucerne meal at 0±160 g/kg diet, broilers grown to 21 days showed no differences (p>0.05) in growth rate, food intake or food ef®ciency. The apparent metabolisable energy (MJ/kg) of diets containing 40 and 80 g SPV/kg was higher (14.1± 14.6) than the speci®c dietary concentrations of SPV at other levels.#2000 Elsevier Science B.V. All rights reserved.
Keywords:Sweet potato vines; Evaluation with broilers; Chemical composition; AME
1. Introduction
In many countries, particularly in the low-income countries, feedstuffs for poultry are often scarce. There is therefore a need to identify by-products that may be useful for poultry in these countries. Sweet potatoes (Ipomea batatas) are the staple food for many people in low-income countries and the vines are often discarded or fed to ruminant livestock. Occasionally, they are dried under the sun and used to feed pigs and poultry but
85 (2000) 145±150
*Corresponding author. Tel.:61-7-3824-3081; fax:61-7-3824-4316.
E-mail address: farreld@dpi.qld.gov.au (D.J. Farrell)
little is known of their nutritional value. Yield of sweet potato vines may be up to 2.6 metric tonnes of dry matter/ha (Villareal et al., 1979).
The purpose of the experiment described here was to determine the chemical composition of sweet potato vines (SPV), to compare their nutritional value with that of lucerne meal and to replace lucerne meal with the milled vines at different levels in starter diets for broiler chickens.
2. Materials and methods
Sweet potato vines were pruned at regular intervals from a range of cultivars grown in small plots at the Centre for Amenity Horticulture, Queensland Horticulture Institute, Cleveland, Queensland. They were sun-cured in batches and hammer milled to a suitable particle size for inclusion in chick starter diets fed in mash form. The vine meal replaced, in incremental amounts, lucerne meal included at a maximum of 160 g/kg. The lucerne meal was cut at the early ¯owering stage and sun cured before milling. The composition of the diets formulated to nutrient speci®cation for starter chicks (SCA, 1987) is given in Table 1.
The ®ve diets were fed to groups of eight 1-day-old male chickens per cage (65 cm long35 cm wide42 cm high), blocked according to diet and housed in a heated room, initially at 338C and gradually reduced to 228C at 21 days. Each dietary treatment was
Table 1
Ingredient and calculated chemical composition (g/kg) of sweet potato vine (SPV) based diets on `as fed' basis
Ingredients Control 4 SPV
Lucerne meal 160 120 80 40 0
Sweet potato vine meal 0 40 80 120 160
Sorghum 244.2 243.8 243.3 242.9 242.4
Wheat 250 248 245 242.5 240
Soybean meal (48%) 185.4 188.5 191.6 194.8 198
Fish meal (65%) 60 60 60 60 60
Meat and bone meal (50%) 33.4 33.3 33.3 33.3 33.2
Soybean oil 49.6 49.7 49.9 50 50
Limestone 5.0 4.8 4.7 4.5 4.3
Salt 1.31 1.3 1.4 1.4 1.4
Vitamins and minerals 7.1 7.1 7.1 7.1 7.1
DL-Methionine 3.03 3.0 3.0 2.9 2.9
L-Lysine HCl 0.99 0.92 0.85 0.79 0.72
Chemical composition(g/kg) (Calculated as total basis)
Crude protein 222 221 222 222 221
AME (MJ/kg) 12.50 12.50 12.50 12.50 12.50
Lysine 12.50 12.50 12.50 12.50 12.50
Methionine 6.3 6.3 6.3 6.3 6.3
Methcyst 9.12 9.12 9.12 9.12 9.12
Tryptophan 2.8 2.9 2.9 2.9 3.0
replicated four times. Food intake and body weight were measured at 21 days of age. During the last 4 days of the experiment, food intake was measured quantitatively and all excreta were collected daily on plastic trays placed under the cages. The excreta were frozen and subsequently dried at 758C for 48 h and sub-sampled and with food samples combusted in a bomb calorimeter. Apparent metabolisable energy (AME) of the diets was then calculated. Chemical composition of the dried vines and lucerne meal was determined using the methods of the AOAC (1990).
Amino acid analysis was undertaken by ion-exchange chromatography (Waters HPLC) after hydrolysis with 6 M HC1 at 1108C for 18 h under re¯ux conditions (Spackman et al., 1958; Finlayson, 1964). Cystine and methionine were determined as cysteic acid and methionine sulphone respectively, following performic acid oxidation (Moore, 1963). Tryptophan was not determined.
Mineral elements were measured using inductively coupled plasma (ICP) atomic emission spectrometer (Baker and Smith, 1974).
Data were analysed using a protected analysis of variance (ANOVA) and regression analysis. Treatment means differences were examined for signi®cant effects (p<0.05) using the least signi®cant difference test (Statistix Analytical Software, 1985).
3. Results
Shown in Table 2 is the chemical composition of the SPV and lucerne meals. Almost 500 g/kg of the components of SPV meal were neutral detergent ®bre and almost 400 g/ kg for the lucerne meal. Crude protein content was 190 and 182 g/kg for the SPV and lucerne meals, respectively. Amino acid analysis showed a reasonable balance, with a total sulfur amino acid content of 4.7 g/kg (Table 3). Lucerne meal contained higher levels of several of the important amino acids such as lysine, threonine and valine than SPV meal. Mineral analysis (Table 3) showed very high levels of iron and manganese and a reasonable content of calcium (10.5 g) in SPV meal whereas lucerne meal had a high level of potassium.
There were no differences (p>0.05) in food intake, liveweight gain or food conversion ratio (FCR) among chicks fed diets containing different concentrations of SPV (Table 4). However, there was a tendency for growth rate to decline at the two highest levels of SPV meal inclusion.
Table 2
Chemical composition (g/kg DM) of sweet potato vines (SPV) and lucerne meal
SPV meal Lucerne meal
The AME of the diets containing 40 and 80 g SPV meal/kg was numerically higher (p<0.05) than that of the other three diets; this suggests that the vines had a higher AME value than the lucerne meal at these two levels of inclusion. Furthermore, there was no difference in the AME of the two diets with the highest level of inclusion of SPV and those of diets containing the same levels of lucerne meals.
Linear regressions between rate of inclusion (x) and responses (y, AME and FCR) were calculated but were not signi®cant (p>0.05).
4. Discussion
The chemical composition of SPV meal tested in this study is similar to that reported by Villareal et al. (1979); the high ash content of 170 g/kg is also almost identical to
Table 3
Amino acid (g/kg DM) and mineral composition of dried sweet potato vines (SPV) and lucerne meal
SPV meal Lucerne
Alanine 7.8 9.40 Calcium 10.5 9.9
Arginine 7.45 8.50 Phosphorus 2.4 2.5
Aspartic acid 18.7 21.0 Magnesium 3.7 2.7
Cystine 2.1 2.50 Potassium 5.8 17.8
Glutamic acid 15.7 16.9 Sodium 2.8 0.67
Glycine 7.2 8.8 Sulfur 3.4 2.8
Histidine 2.6 4.0
Iso-leucine 5.7 7.9 Iron 2029 853
Leucine 10.8 13.1 Copper 15 0
Lysine 6.2 9.6 Zinc 39 62
Methionine 2.6 2.5 Manganese 308 34
Phenylalanine 6.9 5.1 Boron 51 27
Proline 5.5 9.8 Aluminium 192 463
Serine 5.6 9.8
Threonine 5.6 8.1
Valine 7.2 9.4
Table 4
Food intake, live weight gain and food conversion ratio of chickens grown to 21 days of age and the apparent metabolisable energy (AME) of the ®ve diets (MJ/kg DM) with different levels of sweet potato vine (SPV) meal replacing lucerne meal
Diet (g/kg) Food intake (g) Weight gain (g) at 21 days
Food conversion ratio
AME
0 SPV 867 601 1.447 13.81
40 SPV 883 610 1.449 14.20
80 SPV 870 614 1.444 14.67
120 SPV 857 584 1.469 13.89
160 SPV 831 579 1.461 13.75
178 g/kg shown in Table 2 and is much higher than that of lucerne meal. However, during analysis some of the ash appeared visually to be in the form of silica suggesting possible contamination of SPV with soil. At the highest level of inclusion (160 g/kg) of lucerne meal and SPV meal, AME values of these diets were surprisingly high (13.7±13.8 MJ/kg DM). Cilliers et al. (1994) reported an AME of milled lucerne hay of only 4.0 MJ/kg using adult cockerels. This would be expected to be even less for young chickens. Ravindran and Blair (1992) give an AME of 6.2 MJ/kg DM for SPV meal which is more in line with that found in the current studies (Table 4). It was not possible to determine the AME value of SPV per se. The main objective was to compare it with lucerne meal. The diets were formulated to 12.5 MJ AME/kg on an `as fed' basis. When adjusted to a dry matter basis, the measured value was similar to that for the 0 and 160 g SPV/Kg diet of 13.6 MJ AME/kg.
There is no obvious explanation for the increased value in AME of diets 2 and 3 other than a stimulatory effect of SPV at these levels on hind gut micro¯ora and hence increased fermentation. Diet 3 containing 80 g SPV/Kg gave the highest growth rate, the highest AME and the lowest FCR.
We were unable to ®nd any published results feeding experiments with chickens using SPV meal; the reason is probably because sweet potatoes are grown mainly in low-income countries which do not normally have extensive research facilities and sophisticated equipment to evaluate feedstuffs. According to Ravindran and Blair (1992) SPV meal is a good source of protein and pigments for poultry (Garlich et al., 1974) and it contains no anti-nutritional factors. Despite the lower contents of some of the important amino acids in SPV meal compared to lucerne meal, growth rate and FCR were not different even when each was included at 160 g/kg in diets. For intensively farmed broiler chickens, the ®bre level is too high to allow signi®cant inclusion in diets (5 g/kg). For village chickens, which have lower production and hence lower dietary requirements, SPV meal could be a useful form of protein supplement and not greatly different from that of lucerne meal.
Acknowledgements
We thank the staff at QPRDC for their technical assistance, Stuart Scott and his staff at the Centre for Amenity Horticulture, Queensland Horticulture Institute, Cleveland for providing the fresh sweet potato vines, Mike Nielsen for chemical analysis and AusAid for a scholarship awarded to Huda Jibril.
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