Effect of dietary protein level and duckweed (Lemna spp) on reproductive performance of pigs fed a diet of ensiled cassava root or cassava root meal

Le thi Men, Bui Hong Van, Mai thi Chinh and T R Preston¹

Cantho University, Cantho, Vietnam

Abstract

A trial was carried out during an 18 month period, from February 1995 to June 1996 at the experimental farm of Cantho University. The experimental animals were 16 local Baxuyen sows mated to Yorkshire boars. The trial was designed as a 2^*2 factorial with two levels of protein in pregnancy (200g vs 150g/sow/day) and two levels of duckweed (Lemna spp) (0 vs 50% substitution of the protein allowance) for pregnant and lactating sows. The treatments were applied during the first and second reproductive cycle (pregancy plus lactation).

The basal diet in the first cycle was ensiled cassava root, and in the second cassava root meal, as complete replacement for cereals with a protein supplement (50% fishmeal and 50% soya bean meal). On the duckweed treatments, the protein allowance (150 or 200 g/day during pregnancy and 400 g/day during lactation) was reduced to half and duckweed fed ad libitum.

The parameters litter size, litter weight and total feed DM during lactation per unit weight piglet were not affected by the level of protein but were improved significantly by feeding duckweed. It is concluded that a diet of ensiled cassava root, or cassava root meal, with 75 g protein per day in pregnancy and 200 g/day during lactation, plus fresh duckweed ad libitum, can completely replace a conventional cereal-based diet for sows.

Key words: Pigs, sows, reproduction, lactation, protein level, duckweed, cassava root

¹ Finca Ecologica, University of Agriculture and Forestry, Thu Duc, Ho Chi Minh City, Vietnam

Introduction
Rice production in Mekong delta has improved rapidly, although the by-products predominantly used in animal feeding have become less accessible to farmers as their market price has been increasing faster than the value of animal live weight. The Mekong delta, with a large acid-sulfate soil area, has a good potential for growing of sugar cane and cassava which are relatively tolerant to the acid soils. The large area of water also favours growth of water plants such as water spinach and duckweed.

The results of a trial using simulated sugar cane juice (crude brown sugar and water) as the energy source and water spinach (Ipomoea aquatica) to supply part of the protein allowance showed that this type of diet can replace cereals for breeding sows with no change in performance (Bui Hong Van et al 1994). Another recent development has been the demonstration (Bui Huy Nhu Phuc et al 1994; Ospina et al 1995) that when the energy source contains little or no protein (eg: non-cereal feed resources such as sugar cane juice or cassava root), and the protein supplement has a good balance of essential amino acids (eg: soya bean meal), then the protein level can be reduced to no more than 60% of the standards recommended by NRC (1988). Speer (1990) has discussed the physiological justification for this change.

Table 1 : Composition of experimental diets for pregnant sows (first pregnancy) ECR = Ensiled cassava root)

# 50% fish meal; 50% soya bean meal

The objectives of this study were:

• To confirm that a lower protein level can be used with ensiled cassava root as has proved to be the case with sugar cane juice and cassava root meal
• To determine if duckweed could be used to replace part of the traditional sources of protein.

Materials and methods

Treatments and design
The trial was conducted at the experimental farm of Cantho University from February 1995 to June 1996. The experimental animals were 16 local Baxuyen sows (1st and 2nd farrowings) mated by insemination to Yorkshire boars and studied for two reproductive cycles. The trial was a two-way randomized complete design with level of protein in gestation as one factor and partial substitution of the protein supplement by duckweed as the other factor. The experimental diets used in the first cycle are shown in Tables 1 and 2.

Table 2 : Composition of experimental diets for lactating sows (First lactation)

The diets used for the second reproductive cycle were similar to those used in the first cycle except that cassava root meal replaced the ensiled root.

Feeding and management
First reproductive cycle

Three weeks after the first mating, the sows were fed with the experimental diets. Whole cassava roots (pH = 6.67; HCN= 45 mg/kg fresh root) were washed, chopped to thin chips and raw sugar added at the rate of 5%. The time of ensiling was 3 weeks after which time the pH was 3.62 and the HCN content had decreased to 9mg/kg fresh root. The duckweed was grown in earth-lined ponds fertilized with biodigester effluent as described by Bui Xuan Men et al (1996). During pregnancy, the sows were given a protein supplement (50% fish meal and 50% soya bean meal) at the rate of 150g or 200g/day (treatments without duckweed) and 75 and 100 g/day for the treatments with duckweed. In lactation the amount of protein was 400g/day for each treatment.

The sows were fed ensiled cassava roots during gestation at levels of 2.7–3.0kg/day. During lactation the ensiled cassava was fed ad libitum. The duckweed was fed at levels of 2.7 kg/day in gestation and 4 kg/day in lactation. The piglets were given the same diet (the complete diet containing 18% crude protein) for every treatment and were weaned at 42 days of age.

Second reproductive cycle
The feeding and management procedures were similar to those used in the first reproductive cycle except for the change in the processing of the cassava roots which were dried and ground in the form of meal.

Results and discussion
Effect of level of protein

Mean values for the effect of protein level during gestation on reproductive traits are in Tables 3 and 4 for the first and second reproductive cycles, respectively. The level of protein during gestation had no effect on litter size, litter weights, mean weight of litter, daily gain in weight of piglet to weaning and total feed DM/kg piglet.

This is in agreement with the report of Speer (1990) that a protein level of 147g/day is adequate during gestation provided the protein is well balanced for essential amino acids and that the non-essential amino acids do not exceed 50% of the total amino acids.

Effect of level of duckweed
Mean values for the effect of duckweed on reproductive traits are in Tables 5 and 6. Most traits were significantly improved by replacing half the soya bean and fish meal supplement with fresh duckweed. Bui Xuan Men et al (1996) reported similar results for ducks.

The results imply that duckweed protein, as well as being highly digestible (Rodriguez et al 1996), has a good array of essential amino acids. It also has a high concentration of major and minor minerals, and it provides a rich source of vitamin A precursors, particularly carotene, and pigments such as xanthophyll (Leng et al 1995).

Conclusions

The results of this experiment indicate that:

• Ensiled cassava roots (or cassava root meal) can replace cereal grain as the basis of pig diets
• The protein allowance of sows during gestation can be reduced to 150g/day with no loss of performance
• Replacing half the conventional protein sources (soya bean meal and fish meal) with fresh duckweed can improve reproductive performance of sows.

Acknowledgements

This research was supported by the International Foundation of Science through a grant (B/2232–1) to the senior author.

References

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