Effects on sow reproduction and piglet performance of replacing soybean meal by a mixture of sweet potato leaves, water spinach and fresh cassava foliage in the gestation and lactation diets of Mong Cai and Yorkshire sows

Hoang Nghia Duyet, Truong Thi Thuan and Nguyen Duc Son

Hue University of Agriculture and Forestry
Hue, Vietnam
duyethue2004@yahoo.com

Abstract

The effects on the reproductive performance of Mong Cai (MC) and Yorkshire (Y) sows of three levels of foliage in the diets in gestation and lactation were evaluated. Dietary treatments 0L, 50L and 100L corresponded to replacement of 0, 50 and 100%, respectively, of the soybean meal in gestation and lactation diets by a foliage mixture consisting of equal parts of water spinach, cassava leaves and sweet potato leaves on a dry matter (DM) basis.

DM and nutrient intakes were not affected by treatment in gestation. Litter size at birth was not influenced by dietary treatment, but mean piglet live weight and total litter live weight (LW) at birth were significantly lower (P<0.05) in treatment 100L for Y sows. Treatment 100L resulted in significantly lower mean piglet and total litter weaning weight for both MC and Y sows, but the differences between 0L and 50L were not significant. Sow feed consumption to produce 1 kg of piglet at weaning was higher in treatment 100L than in 0L and 50L, although feed cost per kg of piglet was lower. Sow LW losses during the lactation period, and weaning to service interval, were higher for treatment 100L for both MC and Y sows. The differences for all other parameters measured between 50L and 0L were small and non-significant.

It is concluded that the optimum level of replacement of soybean meal by a mixture of foliages in pregnancy and lactation diets is 50% for both MC and Y sows. MC sows appear to be better adapted to high levels of foliages in the diet than Y sows.

Keywords: Cassava leaves, Mong Cai sows, piglet performance, reproduction, sweet potato foliage, water spinach, Yorkshire sows.

Introduction

In Vietnam around 285,000 ha are used for growing sweet potato, nearly 300,000 ha for cassava and about 250,000 ha for water spinach (Lich Le Ba 1996; Nga Lam Quanget al 2000). Biomass yield of sweet potato is high (50 tonnes of foliage and 30 tonnes of roots/year (Hoang Vu Tuyen et al 1993; Cach Nguyen Thi1997), and Vietnam's hot and humid tropical climate provides very good conditions for plant growth all year round. The crude protein (CP) content in the leaf is between 26 and 33% of DM, and in the stem 10 to 14% (Woolfe 1992; Ishida et al 2000). In cassava leaves, the DM content is 25 - 26% and CP content 27% in DM. Water spinach contains 10 - 11 % DM and around 21% CP in DM. Therefore, sweet potato leaves, cassava leaves and water spinach are potentially valuable as protein sources for pigs, and can be harvested several times throughout the year (Dahnia et al 1981; Hong Vu Tuyen et al 2003; Le Van An 2004).

Vietnam has about one million Mong Cai (MC) sows (50% of the total sow population), concentrated in Northern and Central Vietnam (Lich Le Ba 1996). However, recently Yorkshire (Y) pigs have been imported in order to improve pork quality.

Traditional feeding of MC sows in Central Vietnam is based on large amounts of vegetables, such as sweet potato leaves, water spinach, and fresh cassava foliage, and as energy sources inexpensive materials such as rice bran and cassava root meal. The prices of these feeds are currently: rice bran, 2200 VND/ kg; cassava root meal, 1500 VND/ kg; maize 2500 VND/ kg; broken rice 2800 - 3000 VND/ kg and soybean meal 10 000 VND/ kg. Sweet potato leaves, water spinach and fresh cassava foliage are grown in gardens or in nearby fields through the year. These forages are very useful as feeds for MC sows, because the sows do not become so fat during pregnancy, and the milk production is higher. They also provide vitamins and minerals, and Duncan et al (1960) reported that the positive effect of vitamin and mineral levels on sow reproductive performance is more important than high protein levels. Men Le Thi et al. (2000) and Duyet Hoang Nghia et al. (2003, 2004) showed that the most suitable proportion of sweet potato leaves in the diet of MC sows is from 30 to 40 % (in DM) in pregnancy, and 20 to 30 % in lactation. However, little research has been done on the use of mixtures of leaves for feeding MC sows as replacement for conventional protein sources. In view of the rapidly increasing price of soybean meal, it is important to find alternative protein sources, and the objective of the study was to evaluate the effect of these on sow reproduction.

Material and methods

Experimental design:

Two factors were tested, breed and protein source:

Breed:

Nine local MC sows and nine Y sows were used in the experiment, and were followed for one complete reproductive cycle.

Protein source:

Soybean meal and a mixture of water spinach, cassava leaves and sweet potato leaves were compared as protein supplements.

Three dietary treatments were compared:

0L: 100% of dietary protein supplied by soybean meal (no green foliage supplied).
50L: 50% of the protein was supplied by soybean meal and 50 % by a mixture of water spinach, cassava leaves and sweet potato leaves (equal parts of each foliage on DM basis)
100L: 100% of the protein was supplied by water spinach, cassava leaves and sweet potato leaves (equal parts of each foliage on DM basis).

The experimental model is shown in Table 1.

Table 1. Experimental model and feed allowances
	0L	50L	100L
Number of MC sows	3	3	3
Number of Y sows	3	3	3
CP from soybean meal (%)	100	50	0
CP from mixture of foliages (%)	0	50	100
CP in the diet DM (%)	13.0	13.0	13.0
Daily feed allowance, kg DM /day
First 3 months of pregnancy, MC sows	1.5	1.5	1.5
Last 3 weeks of pregnancy, MC sows	1.7	1.7	1.7
First 3 months of pregnancy, Y sows	2.0	2.0	2.0
Last 3 weeks of pregnancy Y sows	2.5	2.5	2.5
Lactation period (both MC and Y sows)	Ad-lib	Ad-lib	Ad-lib

Growing and processing of the foliages and experimental diets:

Sweet potato, water spinach and cassava plants were purchased from local farmers, and were harvested by taking some of the leaves from cassava and sweet potato plants grown for root production. Water spinach is grown in the low-lying areas of the farms and both leaves and stems were harvested. The foliages were chopped into 0.5 -1 cm lengths and mixed in the ratio of 1:1:1 (DM basis) (8, 10 and 4 parts by weight, respectively, on fresh matter basis) and then fed the following day. Before feeding, the foliages and concentrate meals were weighed and mixed according to treatment, and the rations were fed 2 or 3 times per day. The chemical composition of the dietary ingredients and experimental diets is shown in Tables 2 and 3.

Table 2. Chemical composition of the dietary ingredients (in DM except for DM which is on as fed basis)
		On DM basis			VND / kg
	DM (%)	CP (%)	Lysine (g/kg)	Kcal ME
Rice bran	87.8	11.6	6.38	2901	2200
Cassava root meal	87.4	3.3	1.65	3670	1500
Soybean meal	88.5	41.8	27.90	3800	11300
Sweet potato leaves	13.4	17.8	8.06	2261	2250
Water spinach	10.6	19.8	9.34	2547	2830
Cassava leaves	25.7	25.6	13.6	2820	2330

Table 3. CP, ME and price of experimental diets
Diet	CP (g/kg DM)	ME (kcal/kg DM)	Fresh wt (kg) of 1 kg DM	Price/kg DM (VND)
0L	133	3 225	1.14	3 194
50L	133	3 125	7.29	2 671
100L	133	2 947	6.75	2 131

Animals:

Nine MC and nine Y sows in parities 3 to 5 were selected from Tien Phong farm. Initial live weights were 80 - 90 kg for the MC sows, and 180- 200 kg for the Y sows. Within breed they were allocated at random to the three diets. All sows were mated by AI with semen from the same Y boar and were kept in individual pens with concrete floors. The sows were fed the experimental diets three weeks after mating.

The amount of feed (DM basis) was the same within breed and treatment (Table 1). In the lactation period the sows were fed increasing amounts up to five days after farrowing, and from then onwards feed was offered ad libitum.

Stastistical analysis:

Data were treated by analysis of variance (ANOVA) using the General Linear Model (GLM) of the MINITAB (2000) software. Sources of variation were diet, breed, interaction diet x breed and error

Results and discussion

Daily allowances were restricted during pregnancy, and there were no feed refusals. The foliage mixture made up 25% of the DM of diet 50L and 40% of the DM of diet 100L. In lactation, neither of the breeds was able to consume the planned amount of dry matter on the forage diets (Figure 1) which was only about 80% of the planned amount for the 100L diets. There was an indication that the Mong Cai sows were able to consume more than the Yorkshire sows on the all-forage supplements.

Figure 1: Amounts of DM consumed during lactation expressed
as a fraction of the 0L diet = 1

Table 4. Effect of breed and foliages on sow performance in pregnancy (kg)
	MC			Y
	0L	50L	100L	0L	50L	100L
Live weights of sows
At mating	80.3±1.2	85.0± 2.0	83.3± 1.8	183± 4.6	184± 2.7	188 ± 1.8
At farrowing	96.0± 1.0	98.7± 1.2	94.7± 2.3	208± 5.0	205± 2.7	210± 46
At weaning	83.0±1.2	82.3±0.3	78.0±2.1	174±3.5	170±0.9	165±2.9
Change in pregnancy	15.7±0.3	13.7±0.3	11.3±0.9	25.3±1.2	21.3± 0.3	22.3± 2.9
Litter data
Size at birth	10.7±0.3	11.0± 0.6	10.3±0.3	10.3±0.3	10.7± 0.3	10.3± 0.3
Weight at birth	6.8± 0.15	6.7± 0.29	6.1± 0.22	13.2± 0.3^a	13.2± 0.43^a	11.4± 0.7^b
^a,b Means within row and breed with different superscripts are different at P<0.05

Live weight at mating and farrowing, live weight gain during pregnancy, and litter size and weight at birth did not differ among treatments (Table 4), and were within normal ranges for the two breeds. Litter birth weight from MC sows was not affected by diet, but for the Y sows litter live weight at birth was lower in treatment 100L (P<0.05), probably as a result of the lower DM intakes of the sows on the high foliage diet.

Total litter weight at 21 days of age did not differ between treatments 0L and 50L, in both MC and Y sows, but was lower on the 100L diet (Table 5). Litter size at weaning was not affected by diet in both MC and Y sows. Feed conversion ratio (kg feed/ kg piglet) was better for treatments 0L and 50L compared with 100L and for both MC and Y sows. The cost of producing 1 kg of piglets live weight was lower in treatments 50L and 100L, than in treatment 0L for both MC and Y sows.

Live weight losses during lactation were higher in treatment 100L than in 0L and 50L and was more marked in Y than in MC sows. As a result of the greater live weight in lactation, the mean number of days to re-mating of the sows was higher in treatment 100L than in treatments 0L and 50L, with the effect being more marked for Y than for MC sows. The relationship between live weight loss during lactation and days from weaning to mating (Figure 2), and the marked differences between breeds for these parameters (Figures 3 and 4), indicates that the Y sows were less able to adapt to the all-foliage supplement than the MC sows.

Table 5. Effect of breed and foliages on sow and piglet performance in lactation
	MC			Y
	0L	50L	100L	0L	50L	100L
Litter data
Weight 21 days, kg	28.3± 0.8^a	27.5± 0.8^a	23.7±0.9^b	46.7±1.1^a	43.0±1.15^a	36.3±0.88^b
Piglets weaned	10.0±0.57	10.0± 0.27	9.0± 0.00	9.3± 0.33	9.0± 0.58	9.0± 0.0
Weaning weight, kg	80.0±3.5^a	77.9±3.4^a	63.0±1.1^b	92.6± 1.4^a	88.1±4.9^a	78.9±0.08^b
Feed consumed, kg	344±11.4	338±5.6	320±4.0	428±1.0	427±4.7	409±1.9
FCR, kg /kg#	4.3±0.07^a	4.4±0.08^a	5.1±0.11^b	4.6± 0.06^a	4.8± 0.15^a	5.5±0.12^b
FCR, VND / kg	13 628^a	11 723^b	10 804^b	14 787^a	12 908^b	11 787^b
Sow data
Days to service	8.0±0.6^a	9.0±0.6^a	9.7±0.9^b	14.3±1.2^a	16.3±1.2^a	22.7±0.9^b
Loss in lactation, kg	13.0±0.6^a	16.3±2.3^b	16.7±0.3^b	34.3±1.8^a	34.7± 0.3^a	45.0±1.7^b
Loss in lactation, %	13.5±0.6^a	16.5±0.7^a	17.6±0.3^b	16.4±0.6^a	16.9±0.6^a	21.3± 0.5^b
^a,b Means within row and breed with different superscripts are different at P<0.05 #Feed consumed by sow and litter/litter weight at weaning

Figure 2: Relationship between loss in live weight during lactation and
days from weaning to mating (dark blue dots are the Y sows)Conclusions


Figure 3: Mean values for percentage weight loss during lactation for Mong Cai and Yorkshire sows	Figure 4: Mean values for days from weaning to mating percentage for Mong Cai and Yorkshire sows

Conclusions

A mixture of foliages (sweet potato leaves, water spinach and cassava leaves) can replace 50% of a conventional protein supplement for both MC and Y sows without affecting piglet performance or sow reproduction, and resulting in lower feed costs per kg of piglet weight gain.
Using these locally produced by-products will increase the sustainability of the system.
Replacing 100% of the soybean meal by a foliage mixture increases live weight losses of the sows and the interval from oestrus to mating, and reduces piglet weight gains to weaning.
Mong Cai sows are better adapted to high levels of foliage in the diet than Yorkshire sows.

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