Livestock Research for Rural Development 9 (2) 1997

Citation of this paper

An approach to the nutritional value for pigs of sweet potato vines (Ipomoea batatas (l.) lam)

P L Domínguez and J Ly

Instituto de Investigaciones Porcinas
Carretera del Guatao km 1, Punta Brava
La Habana, Cuba

Abstract

Sun-dried sweet potato vine (SPV) meal contained in dry basis (g/kg): 234 crude fibre, 403 NDF, 328 ADF, 160 detergent lignin, 29.2 N, 216 ash and 158 kj/10 g DM gross energy. The effect of feeding SPV on nutrient digestibility was studied in either ileorectostomized or intact 45 kg liveweight pigs fed graded levels of SPV (0, 100 and 200 g/kg in the dry diet). SPV significantly decreased both ileal and faecal digestibility of most nutrients. Estimated ileal and faecal crude protein digestibility of SPV meal was 22.1 and 54.1% whereas in vitro ileal crude protein digestibility of SPV meal accounted for 42.2% thus indicating a rather low availability of crude protein in this biomass. The contribution of the large intestine to the digestion of diets ranged from 19.7 to 20.8% of energy disappearance in the entire digestive tract. Daily ileal and faecal output of short chain fatty acids and ammonia showed a trend to be proportional to the level of SPV meal in the diet. A low level of inclusion of SPV meal in the diet is suggested in order to avoid a negative effect on nutrient digestibility. Methods to improve digestion of this biomass could be encouraged.

Keywords: pigs, sweet potato vine, digestibility, fermentation

 

Introduction

Sweet potato (Ipomoea batatas (L.) Lam) is a tropical crop of a relatively short vegetative cycle the tubers of which are usually employed for human and animal consumption (see Wolfe 1992). The aerial part mostly composed of vines, may be utilized as animal feed in traditional backyard animal production systems. In this connection the possibility of use of sweet potato vines (SPV) for pigs has been explored either alone or together with the tubers (see Dominguez 1992) which in turn have been extensively studied (Nwokolo 1990). Moreover, the use of pigs for biological harvesting of sweet potato crops has long been recognized (Bishop 1957).

There are few data available concerning the feeding value for pigs of the foliage from sweet potato. Ffoulkes et al (1978) and Ruiz et al (1980) have reported a high DM digestibility of SPV in ruminants. However a depressing effect of this type of biomass on animal digestibility has recently been reported for diets offered to growing pigs (González et al 1994; Ly and Diéguez 1995), thus supporting early findings of Zarate (1956).

The aim of the experiments described herein was to obtain information concerning digestion of SPV meal in the pig.



Materials and methods

Diets

Experimental diets were formulated to contain 0 (control), 100 and 200 g/kg SPV meal (Table 1). The aerial part of sweet potato plants was collected at the end of the vegetative period, during tuber harvesting. The sweet potato tubers were destined to human consumption. The foliage was sun-dried and milled to obtain the SPV meal. The analyzed composition of the resulting meal was (g/kg dry basis): 234 crude fibre, 403NDF, 328 ADF, 160 detergent lignin, 29.2 N, 216 ash, 75.5 hemicellulose, 167 cellulose and 158 kj/10 g DM gross energy.

Table 1: Composition of the diets

SPV0

SPV10

SPV20

Ingredients, g/kg DM

Maize meal

747

670

596

Soybean oilmeal

223

201

178

Sweet potato vine meal

-

100

200

CaHPO4.2H2O

10

10

10

CaCO3

5

5

5

NaCl

5

5

5

Vitamins-trace min1

10

10

10

Chemical composition, g/kg DM

Dry matter

925

925

925

Ash

34.3

52.5

70.5

Organic matter

966

9 48

930

Nx6.25

166

168

169

Crude fibre

37.1

56.8

76.5

NDF

115

136

158

Energy, kJ/10 g DM

180

178

176

1 Supplied per kg diet: 27 mg FeSO4.7H2O, 10 mg MnSO4.4H2O,, 15 mg CuSO4.5H2O, 85 mg MgSO4.7H2O, 0.3 mg CoSO4.7H2O, 0.1 mg KI, 0.02 mg Na2SeO3, 1600 IU vitamin A, 300 IU, vitamin D3, 2 mg thiamine, 3 mg riboflavine, 300 mg choline, 15 mg niacin, 5 mg panthotenic acid, 15 mg pyridoxine, 0.5 mg folic acid, 25 µg cyanocobalamin.

Experiment 1

Three castrated male pigs weighing 45 kg liveweight were placed in metabolism cages for a 7 day adjustment period and were fed the control diet (Table 1) after which the animals were surgically prepared with an end-to-end ileo-rectal anastomosis (Green et al 1987). The pigs recovered their appetite seven days after surgery and were fed one of the three diets (Table 1) according to a 3 x 3 Latin square design for a 4-days adaptation period and a 3-days ileal digesta collection period. Pigs were fed two equal portions (9:00 am and 3:00 pm) of feed daily in meal form to total 0.08 kg DM per kg body weight0.75. Drinking water was available ad libitum from nipple waterers.

Ileal digesta was collected as described elsewhere (Ly et al 1995) and pH, short chain fatty acids (SCFA) and ammonia were estimated in fresh samples as outlined by Ly et al (1995). Ileal digesta was dried 24 hr in a forced-draft oven (60oC), weighed and ground to pass a 1-mm screen using a cyclone-type sample mill. The ground samples were pooled for each pig for each of three days of digesta collection and then subjected to analysis.

Dry matter and ash content were determined on feed and ileal digesta samples by drying at 105oC for 24 hr and ashing at 550oC for 24 hr respectively. Caloric content of feed and ileal digesta samples was determined by bomb calorimetry. Lignin, ADF and NDF were determined by the methods of Goering and Van Soest (1970). Hemicellulose and cellulose were calculated as the difference between NDF and ADF, and between ADF and lignin respectively. Nitrogen was determined on all samples by the macro-Kjeldahl method.

Experiment 2

Table 2. Ileal and faecal flow of fresh content and water

SPV0

SPV10

SPV20

SE

Experiment 1

Ileal flow, g/day/kg DM intake

 

Fresh digesta

2149

2438

2640

±166+

Water

1893

2140

2342

±153

 

Ileal DM, g/100 g

12.0a

12.2a

13.2b

±0.12*

Experiment 2

Faecal flow, g/day/kg DM intake

Fresh faeces

317a

400a

772b

±46*

Water

220a

283b

552c

±33*

Faecal DM,

g/100 g

30.4

29.4

28.5

±1.17

+ P<0,10; * P<0.05

abc Values within a row with the same superscript were not significantly different (P<0.05)

Six castrated male pigs weighing 45 kg liveweight were placed in individual pens containing a stall feeder and a nipple-waterer, in an open front building with solid concrete floors. The animals were fed at random the same diets described in Experiment 1 according to a double 3 x 3 Latin square design for a 6-days adaptation period and one-day faeces collection period, by grab sampling. The level of feed intake was 0.08 kg DM per kg bodyweight0.75 and drinking water was available ad libitum.

The analysis of feed and faeces were carried out as described in Experiment 1. In addition acid insoluble ash was determined by the Van Keulen and Young (1977) technique.

Experiment 3

The pepsin-pancreatin procedure as described by Dierick et al (1985) was employed to determine in vitro crude protein digestibility in SPV meal. In addition the in vivo ileal and faecal N digestibility of SPV meal was calculated by difference according to Crampton and Harris (1969).

Statistical analysis

The results were analyzed statistically following procedures described in Steel and Torrie (1981). Regression analysis was conducted in the required cases.

Results and discussion

Bulking characteristics

Both ileal and faecal bulk were influenced by the introduction of SPV meal in the diet (Table 2). In fact the foliage from sweet potato caused a trend (P<0.10) for ileal fresh digesta to increase from 2149 to 2640 g/day per kg DM intake. This effect was more evident on fresh faeces (P<0.05), which increased from 317 to 772 g/day per kg DM intake. On the other hand ileal DM concentration was increased slightly (P<0.05) by the inclusion of SPV meal in the diet. However, faecal DM concentration was not affected by treatment. Bulking characteristics of digesta and faeces are usually enhanced by dietary fibre in the pig (Bardon and Fioramonti 1983; Bach Knudsen and Hansen 1991) and other animal species (Stephen and Cumming 1980; Nyman and Asp 1982). In this connection, water holding capacity of fibre in SPV meal could at least partially account for the increase in bulking characteristics of digesta and faeces of pigs (Metz 1985).

Table 3. Ileal and total digestibility of nutrients and energy

SPV0

SPV10

SPV20

SE

Ileal digestibility, g/kg

       

Dry matter

738a

703ab

651b

± 26.0*

Ash

409

398

324

±14.2+

Organic matter

764

734

684

±27.2+

Nitrogen

685a

616ab

567b

±11.9*

Crude fibre

179a

281ab

325b

±21.9*

NDF

200a

310b

330b

±35.8*

Energy

723

707

642

±20.8+

Total digestibility, g/kg

       

Dry matter

904a

872a

780b

±12.8*

Ash

624a

626a

422b

±21.3*

Organic matter

914a

889a

799b

±12.6*

Nitrogen

849a

806a

767b

±17.3*

Crude fibre

717a

694ab

451b

±40.2*

NDF

750a

710ab

560b

±51.1*

Energy

914a

889a

799b

±11.7*

+ P<0,10; * P<0.05

abc Values within a row with the same superscript were not significantly different (P<0.05)

Digestibility indices

The apparent ileal digestion coefficients for the diets (Table 3) showed that digestibility of DM and N significantly decreased (P<0.05) when graded levels of SPV meal were included in the feed. This same trend was found for ash, organic matter and energy digestibility (P<0.10). Nevertheless, the reverse was true for ileal crude fibre (P<0.05) and NDF digestibility. On the other hand the depression of total nutrient and energy digestibility was also evident (P<0.05), caused by the dietary SPV meal. In this connection it has been pointed out by Vervaeke et al (1991) and by Shi and Noblet (1993) that some fraction of dietary fibre can disappear anterior to the caecum in pigs. On the other hand, it is well known that the inclusion of fibrous feeds in the diet brings about a depression of several nutrients (see Close 1993).

Apparent energy digestibility (Y, %) correlated with apparent OM digestibility (X, %) in the ileum (r = 0.943; P<0.001) and faeces (r = 0.993; P<0.001) according to the respective regression equations:

Y = - 2.681 + 0.986 ( 0.126) X......(i)

Y = - 0.886 + 1.004 ( 0.040) X......(ii)

Table 4. In vitro crude protein digestibility (%)

Casein

SPV meal

In vivo digestibility1

Ileal

-

22.1±1.6

Total

-

54.1±3.8

In vitro digestibility2

Ileal

96.8±0.3

42.2±1.8

1 Calculated by difference (see text)

2 Mean and standard error of 4 determinations

In vitro crude protein digestibility was low for SPV meal (Table 4). In turn this same value was considerably higher than that obtained for in vivo ileal crude protein digestibility from this type of biomass (22%). In vivo total crude protein digestibility was rather low too (54%). Brown and Chavalimu (1985) found that a substantial increase in the amount of unavailable nitrogenous substances could be a direct effect of drying sweet potato foliage. These findings can support the general trend observed in the present study, but do not provide explanation for the difference between the in vitro and in vivo results. In fact it is generally accepted that this difference accounts for endogenous protein losses (Boisen and Eggum 1991).

Digestion in the large intestine and fermentative indices



Table 5. Contribution of the large intestine in digestion of diets

SPV0

SPV10

SPV20

Digestibility, g/kg

Dry matter

166

170

128

Ash

215

228

98

Organic matter

150

155

115

Nitrogen

165

191

199

Crude fibre

537

413

126

NDF

550

410

280

Energy

190

182

157

Contribution to overall digestion, %

Dry matter

18.3

19.5

16.5

Ash

34.4

36.5

23.2

Organic matter

16.4

17.5

14.4

Nitrogen

19.4

23.6

26

Crude fibre

75

59.5

27.9

NDF

73.3

57.7

40.6

Energy

20.8

20.5

19.7

The addition of SPV meal to the control diet reduced the amount of nutrients and energy disappearing in the large intestine (Table 5) thus largely reflecting the pattern of digestion in the entire gastrointestinal tract. In this connection energy disappearance in the large intestine accounted for some 20% of total energy digestibility in the gastrointestinal tract. These values are in accordance with the data provided by Shi and Noblet (1993). Different fibre fractions were digested in caecum and colon, but the contribution of large intestine to total fibre disappearance in the gastrointestinal tract was largely influenced by the presence of SPV meal in the diet. In fact a decrease in large intestinal digestion of fibre was noteworthy. It was probably due to the nature of the cell wall content in SPV, since detergent lignin accounted for some 40% of the NDF fraction. Although lignin is partially digestible in the pig, low values are usually found for this entity (Low 1985, Close 1993) otherwise bound to beta-linked carbohydrate polymers.

Ileal SCFA concentration was significantly higher (P<0.05) with low levels of SPV in the diet (Table 6) and this same trend was observed in faecal SCFA concentration. However, ammonia concentration was negatively influenced by SPV in both sites of measurement. Ileal pH was significantly higher (P<0.001) as influenced by SPV. This same phenomenum was observed in faecal pH (P<0.01). On the other hand daily flow of SCFA was higher when graded levels of SPV were introduced in the diet either at the ileum (P<0.10) or faeces (P<0.05). The daily flow of ammonia was also higher (P<0.05) in faeces but was indifferent to treatments in the ileum.

Table 6. Ileal and faecal indices of fermentation in pigs

SPV0

SPV10

SPV20

SE

Experiment 1

Ileal concentration, mmol/100 g DM

SCFA

43.6a

87.7b

54.0ab

±5.68*

NH3

15

9.8

8.93

±1.51

Ileal pH

5.89a

6.32b

6.54c

±0.01***

Daily ileal flow, mmol/kg DM intake

SCFA

106

262

189

±29+

NH3

36.9

29.3

30.7

±5.96

Experiment 2

Faecal concentration, mmol/100 g DM

SCFA

49

65.6

48.3

±5.02

NH3

17.2

17.1

14.6

±1.30

Faecal pH

5.90a

6.20b

6.33c

±0.02**

Daily faecal flow, mmol/kg DM intake

SCFA

49.8a

68.7a

104b

±3.95*

NH3

14.7a

20.1a

31.6b

±1.25*

+ P<0,10; * P<0.05; ** P<0.01; *** P<0.001

abc Values within a row with the same superscript were not significantly different (P<0.05)

A decrease in intestinal pH as a consequence of microbial activity on fibre constituents has been suggested to depress ammonia levels in the large intestine (Kauffman 1986). In fact, Varel et al (1984) have found that inclusion of fibre in the diet decreases large intestine ammonia levels. These circumstances would lead to a reduced urinary N output as a result of a decrease in non alpha-amino N absorption through the caecum and colon as it has been observed by Malmlof and Hakansson (1984). This hypothesis could not be proved in this study, since a trend was found of SCFA concentration to increase along with pH values in digesta entering the caecum or faeces. At the same time daily ammonia flow remained unaltered in the distal ileum or increased in faeces, while reducing N digestibility (Table 3) was an effect of the introduction of SPV in the diet.

Based on the experiments described above, methods to improve digestion of SPV meal could be encouraged, otherwise the low digestible energy and N availability of a biomass such as that used in this study does not suggest its inclusion in the diet of the pig.

Acknowledgments

The authors acknowledge Mrs. Martha Caron, Mrs. Maritza Castellanos for technical assistance, Mrs. Olga Martínez for assistance with the statistical analysis and Eng. Rosa María Martínez for typing and computing the manuscript.

References

Bach Knudsen K E and Hansen I 1991 Gastrointestinal implications in pigs of wheat and oat fraction.1. Digestibility and bulking properties of polysacharides and other major constituents. British Journal of Nutrition 65:217-232

Bardon T and Fioramonti J 1983 Nature of the effects of bran on digestive transit time in pigs. British Journal of Nutrition 50:685-690

Bishop E J B 1957 Sweet potato: an excellent feed for pigs. Farming in South Africa 33:42-44

Boisen S and Eggum B O 1991 Critical evaluation of in vitro methods for estimating digestibility in simple-stomach animals. Nutrition Research Review 4:141-161

Brown D L and Chavalimu E 1985 Effect of ensiling or drying on five forage species in Western Kenya: Zea mays (maize stoved), Pennisetum purpureum (Pakistan napier grass), Pennisetum sp. (Bana grass), Ipomoea batatas (sweet potato vines) and Cajanus cajan (pigeon pea leaves). Animal Feed Science and Technology 13:1-6

Close W 1993 Fibrous diets for pigs. In: Animal Production in Developing Countries (Editors: M Gill, E Owen, G E Pollot andT L J Lawrence) British Society of Animal Production Occasional Publication No.16 pp 107-117

Crampton E W and Harris L E 1969 Applied animal nutrition. The use of feedstuff in the formulation of livestock rations. W H Freeman: San Francisco pp 753

Dierick N, Vervaeke I, Decuypere J and Henderickx H K 1985 Protein digestion in pigs measured in vivo and in vitro. In: Digestive physiology in the pig (Editors: A Just, H Jorgensen and J A Fernández) 580 Beretnig Statens Husdyrbrugsforsog: Kobenhavn pp 329-332

Domínguez P L 1992 Feeding of sweet potato in monogastrics. In: Roots, tubers, plantains and bananas in animal feeding (Editors: D Machin and S Nyvald) FAO: Rome pp 217-233

Ffoulkes D, DeB Hovell F D and Preston T R 1978 Forraje de batata como alimento para bovinos: consumo voluntario y digestibilidad de mezclas de forraje de batata (Ipomoea batatas) y caña de azúcar. Produccion Animal Tropical 3:142-146

Goering H K and Van Soest P J 1970 Forage fiber analysis (apparatus, reagents, procedures and some applications. ARS-USDA Handbook No. 379. Washington DC

González C, Veicchonace H and Díaz I 1994a Uso de la batata en la alimentación porcina. III. Digestibilidad aparente de las raíces. In: Informe anual. Instituto de Produccion Animal: Maracay 6(2)

González C, Veicchonace H and Díaz I 1994b Uso de la batata en la alimentación porcina. IV. Digestibilidad aparente del follaje. In: Informe anual. Instituto de Produccion Animal: Maracay 6(3)

Green S, Bertrand S L, Duron M J C and Maillard R A 1987 Digestibility of aminoacids in maize, wheat and barley meal, measured in pigs with ileo-rectal anastomosis and isolation of the large intestine. Journal of Science and Food Agriculture 41:29-43

Kauffmann W 1986 Fermentation in the forestomachs and the hindgut, a comparison. Archive of Animal Nutrition. Berlin 36:205-212

Low A G 1985 Role of dietary fibre in pig diets. In: Recent advances in animal nutrition (Editors: W Haresign and D E Cole) Butterworths: London pp 87-112

Ly J and Dieguez F J 1995 Utilización digestiva de dietas de miel B y altos niveles de fibra en cerdos criollos. Archivos Latinoamericanos de Produccion Animal 3:27-36

Ly J, Macías M, Reyes J L and Figueroa V 1995 Ileal and faecal digestibility of Jerusalem artichokes (Helianthus tuberosus L.) in pigs. Journal of Animal and Feed Science 4:195-205

Malmlof K and Hakansson J 1984 The effect of dietary fibre level on the diurnal pattern of urinary nitrogen excretions in swine. Swedish Journal of Agricultural Research 14:53-57

Metz S H M 1985 The physiological role of dietary fibre in digestion and metabolism of the pig. In: 36th Annual Meeting EAAP:Kallithea 10 pp

Nwokolo E 1990 Sweet potato. In: Nontraditional feed sources for use in swine production (Editors: P A Thacker and R N Kirkwood) Butterworths:London pp 481-491

Nyman M and Asp N G 1982 Fermentation of dietary fibre components in the rat intestinal tract. British Journal of Nutrition 47:357-366

Ruiz M E, Pezo D and Martínez L 1980 The use of sweet potato (Ipomoea batatas (L.) Lam) in animal feeding. 1 Agronomic aspects. Tropical Animal Production 5:144-151

Shi X S and Noblet J 1993 Contribution of the hindgut to digestion of diets in growing pigs and adult sows: effect of diet composition. Livestock Production Science 34:237-252

Steel R G D and Torrie J H 1981 Principles and procedures of statistics: a biometrical approach. (2nd Ed) McGraw Hill Int Book Co: Toronto pp 663

Stephen A M and Cumming J H 1980 The microbial contribution to human faecal mass. Journal of Medical Microbiology 13:45-56

Van Keulen J and Young S A 1977 Evaluation of acid insoluble ash as a natural marker in ruminant digestibility studies. Journal of Animal Science 44:262-266

Varel V H, Pond W G and Yen J T 1984 Influence of dietary fiber on the performance and cellulase activity of growing-finishing swine. Journal of Animal Science 59:388-393

Vervaeke I J, Graham H, Dierick N, Demeyer D I and Decuypere J A 1989 Chemical analysis of cell wall and energy digestibility in growing pigs. Animal Feed Science and Technology 32:55-61

Wolfe J A 1992 Sweet potato: an untapped food resource. Cambridge University Press: Cambridge pp 643

Zarate J J 1956 The digestibility by swine of sweet potato vines and tubers, cassava roots and green papaya fruits. Phillipine Agriculturist 39:78-83

Received 1 May 1997

Go to top