Livestock Research for Rural Development 15 (9) 2003

Citation of this paper

Performance traits of pigs fed sweet potato (Ipomoea batatas L.) foliage ad libitum and graded levels of protein

C González, Ivonne Díaz, H Vecchionacce and J Ly

Faculty of Agronomy, Central University of Venezuela,
PO 2101 El Limón, Maracay, Venezuela
caraujo2@telcel.net.ve
Swine Research Institute, PO Box 1, Punta Brava, La Habana, Cuba
jlyca@yahoo.com


Abstract

A growth trial was conducted with a total of 40 crossbred castrate males and female pigs (1:1) of 29.3 kg mean initial live weight distributed at random into five treatments to study the effect of feeding ad libitum fresh foliage from sweet potato (Ipomoea batatas L.) and graded levels of protein. From 30 to 60 kg the animals received 1.6 kg/day of a feed mix (20.7 MJ/kg) containing 25.1, 23.7, 17.0 or 13.2% protein. From 60 to 90 kg the pigs were fed with 1.8 kg/day of a feed mix (22.0 MJ/g) containing 23.0, 20.6, 14.5 and 9.9% protein. In both periods the animals were fed fresh sweet potato foliage (SPF) ad libitum.

In both periods feed intake decreased (P<0.05) with less protein in the feed. Intake of SPF showed a non linear response (P>0.10) with lower values for intermediate levels of protein in the feed. There was no treatment effect on carcass traits of the animals. For the overall growth and finishing periods, the mean daily gain (721 g) and feed conversion (2.40 kg DM/kg gain) were the best with a combination of 23.7/20.6% protein in the feed supplement (1.6/1.8 kg per day).

It is suggested that it is possible to obtain good performance traits in pigs fed fresh sweet potato foliage ad libitum, provided a feed supplement is given which contains either 23.7and 20.6% or 17.0 and 14.5% protein during the growing and finishing periods, respectively.

Key words: Carcass,  Ipomoea batatas (L.), performance, pigs,sweet potato foliage


Introduction

A trend has been observed in the majority of tropical countries to search for alternative feed resources for animal feeding. This should allow the total or partial substitution of cereals and soybean traditionally employed for feeding pigs. Roots and tubers are amongst those feeds that could potentially substitute the conventional animal feeds, due to their agro-ecological advantages in tropical areas, such as high yields in roots and foliage (Machin 1992). In the particular case of sweet potatoes, the use of foliage as animal feed has received less attention than roots  (Nwokolo 1990; Scott 1992). Even less attention has been paid to the potential advantage of the use of an integrated sweet potato-pig production system (González et al 1994), where the use of roots and foliage in an integral form should decrease the feeding costs in pig production (González and Díaz 1997).

One of the main constraints for the use of tropical foliages could be the high content of the  fibre fractions, therefore determining a decrease in voluntary feed intake and a deleterious effect on performance traits of economic interest (García 1998). In this connection, the use of fibrous feeds for pigs precludes a search for an optimum energy: protein ratio in order to warrant an adequate feed intake (Chiba et al 1991).

The aim of the present experiment was the evaluation of voluntary feed intake of fresh foliage from sweet potato and performance and carcass traits when growing-finishing pigs are fed graded levels of protein in the ration in a tropical environment.


Materials and methods

General

Sweet potato foliage (SPF) was harvested daily from the Faculty of Agronomy farm, at Maracay. A representative sample of this foliage was obtained from the entire period of harvesting, and its characteristics are set out in Table 1. Analyses of the foliage and feeds were conducted at the University following procedures described by the AOAC (1990) and Van Soest et al (1991) for detergent fractions of fibre. Gross energy was determined by bomb calorimetry. All analyses were conducted in duplicate.

Table 1. Chemical composition of the sweet potato foliage

Dry matter

14.6 ± 2.75

Per cent in dry basis

 

Crude protein (N x 6.25)

20.5  ± 3.3

NDF

28.4  ± 3.2

Cellulose

10.7  ± 2.1

Ash

14.9  ± 2.8

Lysine1

0.63

Methionine1

0.29

Gross energy, kJ/g DM

15.9  ± 1.72

1 Calculated

A relatively high protein and low NDF content were outstanding characteristics of the foliage employed in the current study.

Animals and treatments

Forty hybrid pigs (Yorkshire-Hampshire-Landrace-Duroc) of 29.3 kg initial live weight were used in the experiment, which lasted 90 days. The animals were distributed at random according to sex and weight into five treatments. Each treatment had the same number of replications of two pigs (one castrate male and one female). The pigs were housed in 1.5x1.4 m pens in an open stable. The pigs had free access to the dry feed supplement and the sweet potato forage in two feeders and to the nipple water drinkers in every pen. During the trial the live weight of the pigs and feed consumption were recorded every two weeks. Feed refusals were recorded daily.

Five treatments were evaluated during the experiment: a control, conventional diet given ad libitum with no SPF, and another four treatments consisting of  chopped, fresh SPF given ad libitum, and a fixed amount of supplement containing graded levels of protein, which varied in characteristics during the respective growing and finishing periods (Tables 2 and 3). All the supplements had a similar gross energy content.

Table 2. Composition of the protein supplement in the growing period (30-60 kg)

 

 

Crude protein, %

 

Control

25.1

23.7

17

13.2

Ingredients, %

 

 

 

 

 

Maize meal

78.0

41.3

52.0

62.2

72.3

Soyabean meal

17.4

42.3

31.4

20.7

9.90

Palm oil

-

12.5

12.5

12.6

12.8

CaCO3

0.586

0.77

0.8

0.89

0.95

CaPO4H.2H2O

2.42

2.40

2.5

2.5

2.59

NaCl

0.50

0.50

0.50

0.50

0.50

Vitamins y minerals1

0.20

0.20

0.20

0.20

0.20

DL-methionine

-

-

 -

0.07

0.12

DL-lysine

0.60

-

 -

0.30

0.60

Analysis in dry basis

 

 

 

 

 

Gross energy, KJ/g

18.2

21.1

20.9

20.6

20.6

Crude protein, %

17.7

25.1

23.8

17.1

13.3

1 According to NRC (1988) requirements


Table 3. Composition of the protein supplement in the finishing period (60-90 kg)

 

 

Crude protein, %

 

Control

23

20.6

14.5

9.9

Ingredients, % DM

 

 

 

 

 

Maize meal

78.8

46.7

57.2

67.3

77.3

Soyabean meal

17.4

36.9

26.0

15.3

4.52

Palm oil

-

12.5

12.5

12.7

12.9

CaCO3

0.58

0.80

0.87

0.93

0.99

CaPO4H.2H2O

2.42

2.43

2.49

2.56

2.69

NaCl

0.50

0.50

0.50

0.50

0.50

Vitamins & minerals1

0.20

0.20

0.20

0.20

0.20

DL-methionine

-

-

0.03

0.093

0.15

DL-lysine

0.060

-

0.15

0.45

0.75

Analysis in dry basis

 

 

 

 

 

Gross energy, KJ/g

17.9

22.2

22.1

22.1

21.9

Crude protein, %

12.4

23.0

20.6

14.6

9.98

1 According to NRC (1988) requirements


When the animals reached 90 kg live weight they were fasted during 24 hours, then slaughtered for carcass analysis. Carcass yield was calculated prior and after refrigeration at 4oC during 24 hours. Then the different carcass traits were determined in the cold material (Gonzalez et al 2002). In addition all the organs from the digestive system were weighed after being thoroughly washed. The length of the duodenum, caecum and small intestine was established with the aid of a graduated ruler.

The data were analyzed according to a one-way classification and means comparison was made by the Duncan's new multiple range and multiple F test (Duncan1955) as described by Steel and Torrie (1980). The pen with two animals was considered the experimental unit.


Results and Discussion

Performance traits

It was observed that protein intake was similar among pigs fed the control diets and those from treatments with approximately 25 and 23% protein in the supplement (Table 4). Daily protein intake was less (P<0.05) with lower protein content in the supplement. Total DM consumption was reduced when SPF was fed as compared with the control (P<0.05). On the SPF diets, intake of SPF was highest when the protein content of the supplement was lowest. Live weight gain was lower on the SPF diet containing the supplement with the lowest protein content, as compared with all other diets.

The SPF diet in which the supplement had the lowest concentration of protein, and intake of SPF was highest,  resulted in the worst feed conversion, but all other SPF diets were better than the control for this parameter. These results are in agreement with those of Malynicz and Nail (1973) with pigs fed SPF in Papua. It is possible there was a reduced availability of nutrients with increasing levels of SPF consumed by the pigs (Domínguez and Ly 1997) due to an increase in the rate of passage of digesta through the alimentary canal (Díaz et al 1997; Díaz 1998). Poorer availability of nutrients may result in a poor efficiency of feed utilization by the animals.

Table 4. Perfomance traits of growing pigs fed sweet potato foliage (30-60 kg)1

 

 

Crude protein, %

 

 

Control

25.1

23.7

17.0

13.2

SEM

Consumption, kg/day

DM

 

 

 

 

 

 

Supplement

1.97a

1.43b

1.39b

1.40b

1.44b

0.10*

Foliage

-

0.16a

0.16a

0.13a

0.29b

0.01*

Total

1.97a

1.59b

1.55b

1.53b

1.73ab

0.10*

Protein, g

318a

389a

357a

264b

249b

19*

Energy, MJ

35.8

32.7

31.6

31.1

34.8

2.0

Gain, g/day

779a

719a

712a

685ab

597b

52*

Conversion, kg/kg

2.52b

2.23c

2.15c

2.24c

2.89a

0.10*

Days on test1

39a

42ab

43ab

45ab

51b

4*

1 Initial live weight, 29.3 ± 1.3 kg

* P<0.05

ab Means without letter in common in the same row differ at P<0.05

Results for the finishing period (Table 5) were similar to those for the growing period, with lowest DM and protein intake, lowest live weight gain and poorest feed conversion for the SPF diet with the lowest protein content in the supplement.Intake of SPF was not apparently high enough to provide more protein to the animals.

Table 5. Performance traits in finishing pigs fed sweet potato foliage (60-90 kg)1

 

 

Crude protein, %

 

 

Control

23.0

20.6

14.5

9.9

SEM

Consumption, kg/day

DM

 

 

 

 

 

 

Supplement

2.34a

1.45b

1.48b

1.49b

1.50b

0.20*

Foliage

-

0.66a

0.44b

0.41b

0.66a

0.14*

Total

2.34

2.11

1.92

1.90

2.16

0.56*

Protein, g

323b

394a

399ab

291c

265c

28*

Energy, MJ

41.9

42.7

39.7

39.4

43.4

1.8

Gain, g/día

772a

708a

741a

739a

642b

72*

Conversion, kg/kg

3.03a

2.98ab

2.59b

2.57b

3.38a

0.38*

Days in test1

38a

42ab

40ab

40ab

46b

3*

1 Initial live weight, 60.0 ± 1.3 kg

* P<0.05

ab Means without letter in common in the same row differ at P<0.0

Overall (Table 6), pigs fed the supplement with the lowest protein content had the lowest growth rate and poorest feed conversion. There appeared to be a curvilinear relationship between live weight gain and protein intake with the optimum performance predicted to occur when protein intake was about 340g/day (Figure 1). These results could at least be partially explained by the fact that the pigs with the highest and the lowest protein intake had a somewhat higher SPF intake than the pigs which consumed intermediate levels of protein.


Figure 1: relationship between protein intake and live weight gain over the entire growing-finishing period

 

Table 6. Performance traits of pigs fed sweet potato foliage (30-90 kg)

 

 

Crude protein, %1

 

 

Control

25.1/23.0

23.7/20.6

17.0/14.5

13.2/9.9

SEM

Consumption kg/day

DM

 

 

 

 

 

 

Suplement

2.29a

1.68b

1.52b

1.55b

1.57b

0.22*

Foliage

-

0.30a

0.21b

0.18b

0.36a

0.09*

Total

2.29

1.98

1.73

1.73

1.83

0.56

Protein, g

321a

392a

379ab

277c

257c

24*

Energy, MJ

38.8

37.7

35.5

35.0

38.9

1.8

Gain, g/day

733a

714ab

721a

706ab

615b

47*

DM Conversion

3.12a

2.77ab

2.40b

2.46b

3.13a

0.21*

Days on test1

83a

86a

84a

86a

99b

3.9*

1 Initial live weight, 29.3  ± 1.3 kg

* P<0.05

 abc Means without letter in common in the same row differ at P<0.05

According to Keer and Easter (1995), growth rate on a low protein diet could be the same as on a high protein diet, provided there were adequate levels of essential amino acids.  This was not the case in the present experiment where growth rate was depressed on the SPF diet with the least protein, even though the diet was supplemented with lysine and methionine.  However, the protein in the diets used by Keer and Easter (1995) was not derived from foliar sources. In protein-rich foliages, such as SPF, some of the N compounds, including amino acids, could be linked to the cell wall and, therefore, would not be available (Mastrapa et al 1996), as could have been  the case in the present investigation.

The results of the current study do not support the suggestion that feed intake in pigs fed low protein diets is first increased and then declines (Kyriazakis et al 1991; Ferguson and Gous 1997). Whittemore et al (2001) have suggested that many factors contribute to variability of voluntary feed intake in pigs. It is evident that much more information is necessary in the case of pigs fed non-conventional foliages in a tropical environment.

Carcass traits and internal organs characteristics

There was no significant influence of diets on any of the carcass traits evaluated (Table 7). Carcass yields, either in hot or cold state, tended to be lower in pigs fed SPF as compared to those from the control diet. This was probably due to an increased proportion of the live weight being accounted for by the digestive organs (see Table 8).

Table 7. Carcass characterisitcs in pigs fed sweet potato foliage

 

 

Crude protein, %

 

 

Control

25.1/23.0

23.7/20.6

17.0/14.5

13.2/9.9

SEM

Yield, kg

56.6

55.2

55.8

55.3

55.4

1.6

Half carcass, kg

 

 

 

 

 

 

Hot

28.2

27.3

27.3

27.4

27.5

1.1

Cold

27.4

26.6

27.0

26.7

26.9

0.9

Backfat thickness, cm

First rib

3.43

3.84

3.58

3.76

4.17

0.55

Last rib

2.59

2.44

2.82

2.24

2.72

0.60

Last lumbar vertebra

2.25

2.25

2.62

2.41

2.52

0.63

Mean

2.08

2.16

1.75

2.06

2.36

0.40

Longissimus area, cm2

29.86

24.75

29.94

28.50

24.78

5.02

Ham with fat, kg

6.62

6.72

6.80

6.41

6.42

0.53

Ham without fat, kg

5.58

5.43

5.54

5.24

5.13

0.35

Loin with fat, kg

7.89

7.83

7.31

8.11

7.33

0.69

Loin without fat, kg

5.59

5.35

5.14

5.66

5.13

0.87

 

It was observed that pigs fed SPF had significantly longer small intestines and heavier stomachs, small intestines and total digestive organss than the animals fed the control diet, suggesting an adaptation of the gastrointestinal tract to a bulky feed to facilitate digestion and absorption, as was observed by ,Kyriazakis and Emmans (1995).

Table 8. Characteristics of the digestive organs from pigs fed sweet potato foliage

 

 

Crude protein in supplement, %1

 

 

Control

25.1/23.0

23.7/20.6

17.0/14.5

13.2/9.9

SE ±

Absolute weight2

 

 

 

 

 

 

Stomach, g

445a

666b

608b

661b

651b

84*

Duodenum,, g

85

83

86

83

96

18

Pancreas, g

102

121

108

112

95

14

Gall bladder, g

70

76

50

50

93

26

Caecum, g

132

142

140

173

197

43

Small intestine, kg3

1.30a

1.53b

1.54b

1.70b

1.50b

0.22*

Large intestine, kg

1.13

1.05

1.28

1.17

1.19

0.29

Liver, kg

1.25

1.57

1.37

1.40

1.19

0.20

Total weight, kg

4.51a

5.22b

5.18a

5.35b

5.02b

0.20*

Length

 

 

 

 

 

 

Duodenum, cm

59

60

61

61

61

3

Caecum. cm

26

30

27

27

31

4

Small intestine, m

13.6a

15.4b

15.7b

16.5b

16.1b

1.6*

Caecal perimeter, cm

18

20

17

19

20

2

1 Values corresponding to the growing and finishing periods respectively

2 Values adjusted to  90 kg live weight

3 Duodenum not included

*  P <0.05

ab Means without letter in common in the same row differ at P<0.05

Conclusions

It is possible to have a high level of performance (growth and feed conversion) in pigs fed ad libitum sweet potato foliage, provided they also receive a  feed supplement containing 23.7 and 20.6% protein during the growing and finishing period, respectively.


Acknowledgements

The authors thank the librarians of the Swine Research Institute at Havana, Cuba, for assistance in the literature search, and the staff of the Pig Unit, Faculty of Agronomy at Maracay, Venezuela,  for help with feeding and management of the pigs during the  experiment.


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Received 28 January 2003; Accepted 17 August 2003

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