Livestock Research for Rural Development 15 (6) 2003

Citation of this paper

Effect of high dietary levels of sweet potato leaves on the reproductive performance of pure and crossbred Mong Cai sows

Hoang Nghia Duyet, Nguyen Dinh Son, Nguyen Van An and Truong Thi Thuan

Hue University of Agriculture and Forestry
duyethue@yahoo.com

 

Abstract

Twenty four Mong Cai gilts of 8 to 10 kg live weight, after 1 week for adaptation and vaccination, were divided into two groups, each group consisting of 12 gilts. Six Mong Cai gilts in each group were mated with the same Mong Cai boar and six mated with the same Large White boar. The effects on the reproductive performance of two levels of sweet potato leaves (SPL) in gilt (Stage 1), gestation (Stage 2) and lactation (Stage 3) diets were evaluated. Diets LSP and HSP consisted of 20 and 50% SPL in DM, respectively. Diets in the gilt and pregnancy period contained 12% and in lactation 14% crude protein. The sweet potato leaves were fed in the fresh state.

Daily intakes of fresh sweet potato leaves (kg) ranged from 2.0 to 5.0 in the growing phase, 5.5 to 6.0 in gestation and 6.0 to 7.0 in lactation in sows on the HSP diet. In the growing period the low SPL diet resulted in significantly higher mean live weight gain compared to the high SP diet. Mean feed conversion ratios were not significantly different between treatments but the costs of live weight gain were significantly higher for the LSP treatment. The HSP diet resulted in significantly lower live weight gain during gestation, and higher weight losses and longer time for return to heat in lactation. However, litter size at birth and at weaning, and mean birth and weaning weights were not significantly different between treatment groups. The negative effects of HSP on lactation parameters were more marked when Mong Cai sows were mated with the Large white boar.

It is concluded that the optimum levels of SPL in the diet are 50% in the gilt growing and pregnancy periods and 20% during lactation. 

Key words: Gilts, Mong Cai, reproduction, sows,  sweet potato leaves

 

Introduction

Vietnam has about 1 million Mong Cai sows (50% of the total sow population), concentrated in North and Central Vietnam. Traditional feeds of Mong Cai sows in central Vietnam include large amounts of sweet potato leaves in the gilt and pregnancy periods. Farmers only use concentrates, based on for example rice bran and cassava meal, in lactation, in order to give higher milk yields. Pig producers thus make extensive use of locally available products and by-products from agriculture, such as rice bran, cassava, cassava pomace and sweet potato leaves. The pigs produce manure for crops, food and income for small scale farmers.

Thua Thien Hue is a province in the coastal area of Central Vietnam, and around a third of the total area consists of sandy soils, with very poor fertility, but which can be used for growing sweet potato. According to FAO (1997) the productive potential of the sweet potato varies from 24 to 36 tonnes/ha of fresh roots  and from 4.3 to 6.0 tonnes of dry matter/ha of foliage (Morales 1980). It is also possible to obtain up to three harvests yearly (Ruiz et al 1980). The main nutritional importance of sweet potato is in the starch content of the root, but it is also a source of important vitamins, such as vitamin A, ascorbic acid, thiamine, riboflavin and niacin. Recently, it has been shown that the fresh vines can provide up to 27% of the dry matter and 40% of total dietary protein for growing/ finishing pigs. However, so far there has been little research carried out on the most suitable levels of sweet potato leaves for Mong Cai sows, so this study was planned with the following objective: 

 

Materials and methods

Experimental design

The experiment was carried out at Tien Phong Farm, Dien Tho commune, Quang Nam Province in 2001 and 2002.  There were four treatments arranged as a 2*2 factorial, applied to 24 Mong Cai gilts, after weaning (8 to 10 kg live weight).  The main effects were:

After 1 week for adaptation and vaccination the gilts were randomly divided into 2 treatment groups, each group consisting of 12 gilts. Of these six were mated by AI with the same Mong Cai boar and six with the same Large White boar. The experimental design and feed allowances are shown in Table 1.

Table 1. Experimental design and daily feed allowances (n = number of piglets above 8)

 

LSP

HSP

Number of MongCai gilts/sows

12

12

        Mated with Large White boar

6

6

        Mated with Mong Cai boar

6

6

Crude protein content of diet, % of DM

 

 

            Gilt and pregnancy periods

12

12

             Lactation period

14

14

Daily feed allowance, kg DM

 

 

           2-5 months of age

0.6 - 0.9

0.6 - 0.9

           6-8 months of age

1.0 - 1.2

1.0 - 1.2

           First 3 months of pregnancy

1.2

1.2

           Last month of pregnancy

1.5

1.5

           Lactation period

2.5 + 0.25*n 

2.5 + 0.25*n

 

Diets and feeding

The chemical composition of the ingredients and diets are shown in Tables 2, 3 and 4. The sweet potato leaves were fed in the fresh state, immediately after they were harvested. The dry components of the diets were mixed together and fed separately.

Table 2. Chemical composition of the dietary ingredients (% in DM, except for DM which is on fresh basis, and ME which is as MJ/kg)

Ingredient

DM

CP

EE

Ash

CF

ME

Rice bran

87.8

11.6

11.5

6.7

7.9

13.5

Maize

85.5

9.9

5.6

1.3

5.5

16.1

Cassava meal

89.4

2.7

0.5

1.3

2.3

13.8

Sweet potato leaves

13.5

16.3

4.2

7.7

18.0

9.3

Fish meal

89.4

49.3

6.4

16.9

0.8

14.0

 

Table 3. Ingredients (SPL=sweet potato leaves) and cost of the experimental diets, during rearing / pregnancy and lactation (% of DM)

 

LSP

HSP

Ingredient

Pregnancy

Lactation

Pregnancy

Lactation

Rice bran

30

44

15

20

Maize

30

20

18

15

Cassava meal

15

8

16

10

SPL

20

20

50

50

Fish meal

4

7

-

4

Minerals

0.5

0.5

0.5

0.5

Salt

0.5

0.5

0.5

0.5

Total

100

100

100

100

Composition, % in DM (except for ME which is in MJ/kg DM)

Crude protein

12.0

14.0

12.0

14.0

Crude fibre

8.1

8.4

11.5

11.6

ME

13.4

13.1

11.8

11.7

VND/kg feed*

2100

2230

1500

1650

* Calculated from current local prices (VND) for 1 kg: rice bran, 2000; maize, 2000; cassava meal, 1600; sweet potato leaves, 100; fish meal, 6000

 

Measurements

 Growth rate, back fat thickness, feed intake, feed conversion ratio (FCR), and live weight gain were recorded during the growing and gestation periods. Litter size at birth and at weaning, birth weight and weaning weight, mortality of the piglets at birth, total litter weight at 21 days, live weight changes of the sows during lactation, interval from weaning to oestrus, feed intake, and  FCR for producing 1 kg of piglets at weaning were also calculated. Feed ingredients and diets were analysed for proximate constituents by AOAC (1998) procedures.

 

 Results and discussion

The intakes of fresh sweet potato leaves reached from 6 to 7 kg/day in the sows on the HSP treatment during lactation (Table 4), indicating that the palatability or bulkiness of this component of the diet did not appear to be a limiting factor.  The growth rates of the gilts were higher than reported previously for this breed (Hoang Nghia Duyet and Nguyen Kim Duong  1995), and did not differ between dietary treatments.  The cost per 1 kg live weight gain was lower for the HSP treatment, due to the lower cost of the HSP diet. This means that at current feed prices there are economic advantages from using a high level (50%) of sweet potato leaves in diets for growing gilts of the Mong Cai breed. 

Table 4. Effect of low (LSP) or high (HSP) dietary content of sweet potato leaves on intake of leaves, live weight change (means ±SE) and feed conversion of Mong Cai gilts

 

LSP

HSP

Prob.

Intake fresh SP leaves, kg/day

 

 

 

Growing stage

1.0 – 2.0

2.0 – 5.0

 

Pregnancy

2.0 – 2.5

5.5 -  6.0

 

Lactation

3.7 – 4.5

6.0  - 7.0

 

Live weight, kg

 

 

 

Initial

9.6±1.08

11.3±1.35

0.07

Final (after 5 mths)

43.9±2.35

42.0±2.0

0.40

Daily live weight gain, g

224±10.3

205±10.9

0.40

FCR, kg feed/kg gain

4.47

4.67

 

Feed cost/kg gain, VND

9968

7705

 

 

Litter size at birth and weaning, time for farrowing, birth weight and weaning weight were not significantly different between dietary treatments. Weight gain of the sows during pregnancy was lower for the LSP sows (P=0.03), and weight loss during lactation  higher (P=0.007) than for the LSP sows (Table 5). The explanation for this is the approximately 11% lower ME content of the HSP diets compared to the LSP diets, the probably lower crude protein digestibility as a result of the higher crude fibre content and the poorer amino acid balance (SPL replaced fish meal in the HSP diet). Similarly, back fat  thickness was lower, and number of days for return to heat higher for the sows on the HSP diet (P<0.05).  This means that as much as 50% of SPL can be included in gestation diets for Mong Cai sows, but that the level of inclusion in lactation diets should be lower.

Table 5. Means (±SE) for effects of low (LSP) or high (HSP) dietary content of sweet potato leaves on the reproductive performance of Mong Cai sows 

 

LSP

HSP

Prob.

Weight gain in pregnancy, %

23.8±8.3

16.6±5.4

0.03

Litter size at birth

13.9± 2.2

13.1 ±1.50

0.35

Time for farrowing, minutes

74.6±21.1

80.2±25.7

0.60

Piglet birth weight, kg

0.67± 0.09

0.63 ± 0.06

0.32

Total litter weight at 21 days, kg

24.0± 1.6

22.6±1.71

0.06

Litter size at weaning

8.7±0.95

8.7± 1.57

1.0

Piglet weight at weaning, kg

6.9± 0.83

6.5±0.54

0.17

Weight loss in lactation, %

14.1±3.0

17.6±2.02

0.007

Back fat at farrowing, mm

26.0±2.5

21.2 ± 0.92

0.001

Return to oestrus, days

7.9±1.5

10.5±2.12

0.005

Live weight gain during pregnancy tended to be higher (P=0.08) in  sows fed the LSP diet and mated with the MC than the LW boar, but there was no effect of sire breed on this trait for sows fed the HSP diet (Table 6). Weight loss in lactation was greater in sows fed the HSP diet and mated with the LW compared with the MC boar but this trait was not affected by sire breed in sows fed the LSP diet. Litter size at birth and at weaning, and farrowing time were not affected by sire breed in sows fed LSP or HSP diets. Piglet birth and  weaning weights were higher from sows mated with the LW compared with MC  boar on both LSP and HSP diets. In sows fed the LSP diet, back fat thickness at farrowing and days for return to oestrus were not affected by sire breed, but the former trait was reduced and the latter increased in sows mated with LW on the HSP diet.

Effects of sire breed on piglet weights almost certainly reflected the greater size of the LW compared with the MC boar. Similarly, loss of weight and body condition and delayed return to oestrous in LW*MC sows are likely to be due to the greater milk demand of the heavier LW cross piglets.

Table 6. Mean values (±SE) of effect of breed of boar (Large White, LW or Mong Cai, MC) on the reproductive performance of Mong Cai sows given diets including 20 (LSP) or 50 (HSP) % of sweet potato leaves

 

LSP

 

HSP

 

 

MCxMC

MCxLW

Prob.

MCxMC

MCxLW

Prob.

Weight gain pregnancy, %

28.4±6.4

19.2±7.8

0.08

16.3±4.8

16.8±6.4

0.87

Litter size at birth

14.4± 2.7

13.4 ±1.7

0.49

12.8±1.6

13,4±1.5

0.58

Time farrowing, minutes

72.0±13.0

77.2±28.6

0.84

74.0±26.1

86.4±26.6

0.67

Piglet birth weight, kg

0.61±0.03

0.73±0.1

0.02

0.60±0.1

0.67±0.1

0.04

Litter weight 21 days, kg

23.9± .0

24.1±1.2

0.15

22.3±1.5

22.9±2.0

0.60

Litter size at weaning

8.6±1.1

8.8±0.8

0.76

8.6±0.9

8.8±2.2

0.85

Piglet weight weaning, kg

6.3±0.4

7.6±0.4

0.003

6.1± 0.3

6.9±0.4

0.01

Weight loss lactation, %

13.7±1.7

14.5±4.1

0.69

16.9±1.6

18.3±2.3

0.01

Back fat, mm

26.8±1.3

25.2±3.3

0.34

21.6±0.5

20.8±1.1

0.01

Return to oestrus, days

7.0±1.6

8.8±0.8

0.10

9.4±1.6

11.6±2.1

0.01

 

Feed conversion, expressed as amount of feed required to produce 1 kg of weaned piglets, was lower for MC*LW crossbred piglets than for purebred MC piglets, and tended to be lower for piglets from sows fed LSP rather than HSP (Table 7). However, total feed costs were reduced as the content of SP leaves was increased (HSP vs LSP), thus the gross margin of sale value of piglets - feed cost was in favour of the HSP diets. Gross margins did not differ between sire groups of piglets from sows fed the LSP diets but favored the purebred MC piglets from sows fed the HSP diets.

Table 7. Quantity and cost of feed required to produce a litter of weaned piglets and gross margin (sale value of piglets – feed cost)

 

LSP

HSP

 

MCxMC

MCxLW

MCxMC

MCxLW

Feed DM, kg

305

312

308

318

Litter weight, kg

53.2

67.0

52.0

60.1

FCR, kg/kg

5.8

4.7

5.9

5.4

Feed cost,’000 VND

629

643

463

478

Piglets, ‘000 VND

991

1005

969

902

Piglets-feed,‘000 VND

361

363

505

424

 

Managing sweet potatoes as a forage crop

 When sweet potatoes are managed as a semi-perennial forage crop, by harvesting the leaves at regular intervals of from 30 to 40 days, the yields can be very high (Table 8).  This degree of productivity is some 5 times higher than when the leaves are harvested at the same time as the roots, for which foliage dry matter yields are reported of  5.36 tonnes / ha (Nguyen Thi Cach 1997),  5.9 to 6.3 tonnes / ha  (Nguyen Tan Yen et al 1996) and 4.3 to 6.0 tonnes / ha (FAO 1997).

Table 8. Observations of the yield of sweet potato leaves (Ipomoea batatas (L) Lam) on a 1000 m2  plot managed as a semi-perennial forage

Parameter

Unit

Amount

Area

m2

1 000

Age of leaves at first harvest

days

40

Fresh leaf yield / harvest

kg

2 000

Harvests / year

number

10 to 12

Fresh leaf yield / year

kg

20 000 to 24000

Fresh leaf yield / ha/ year

kg

200 000 to 240 000

Estimated dry matter yield / ha / year

kg

27 000 to 32 400

 

Conclusions

 

Acknowledgements 

This research was partially financed by the bilateral SAREC project 2000-2002.


References

AOAC  1988  Official methods of analysis, 14th Edition, Association of Official Analytical Chemists Washington, DC.

Hoang Nghia Duyet and Nguyen Kim Duong  1995  Pig breeding in central Vietnam and its improvement. Exploring approaches to research in the animal sciences in  Vietnam. ACIAR proceedings, No. 68. pp. 123.

Morales  A  1980  El clon del boniato CEMSA 74 - 228. Centro de Mejoramiento de Semillas Aglamicas (SEMSA). Villa Clara, Cuba. pp 26.

Nguyen Thi Cach  1997  Yields of a good sweet potato line. p. 17.  Proceedings of a  Workshop, Hue University, 1997.

Nguyen The Yen,  Vu Tuyen Hoang and Pham Xuan Liem  1996  Preliminary results on breeding sweet potato as animal feed, p 92. National workshop on Developing  Vietnamese  Animal Husbandry to year 2000.

Perez R  1997  Sweet potato. In: Feeding pigs in the tropics, p. 130. FAO Animal Production and Health Paper 132. http://www.fao.org/ag/aga/agap/frg/APH132/Contents.htm

Ruiz  M  E,  Pezo  D  and Martinez  L  1980  El uso del camote (Ipomoea batatas (L) Lam) en la alimentacion animal. I. Aspectors agronomicos. Produccion Animal Tropical 5: 157 - 165. http://www.fao.org/ag/aga/agap/frg/tap52/5_2_7.pdf

 

Received 24 March 2003; Accepted 16 June 2003

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