Azolla filiculoides as partial replacement for traditional protein supplements in diets for growing-fattening pigs based on sugar cane juice

Azolla filiculoides as partial replacement for traditional protein supplements in diets for growing-fattening pigs based on sugar cane juice

* Facultad de Ciencias Agropecuarias, Universidad Nacional, Palmira;
** CIPAV, AA7482, Cali, Colombia

The aquatic plant Azolla filiculoides was grown in nine tanks of total area 468 m² and fed as partial replacement (0, 15 and 30%) of the protein in a soyabean-based supplement given in restricted quantities (200 g protein/animal/daily) with fresh sugar cane juice to growing-fattening pigs. The trial was done on a commercial farm in the Valle del Cauca in Colombia (1000 m above sea level; mean temperature 24°C and rainfall 1100 mm).

The recorded productivity of the Azolla during the 5 month period of the trial was high (equivalent to 9 tonnes protein/ha/year). In the growing phase, pig performance decreased as the amount of Azolla in the diet increased. These effects were reversed in the fininishing phase when there was a strong tendency for the pigs fed azolla to grow faster than on the control treatment. The final result was that there were no differences in growth rate among treatment groups for the total period of the trial (from 24 to 89 kg liveweight).

This preliminary information has served to stimulate interest in the growing and use of Azolla as a protein supplement in Colombia. The technology is already being applied on a number of farms with satisfactory results both from the biological and economic standpoint. More importantly, these on-farm activities are generating invaluable information concerning the practice of growing and utilization of this feed resource under varying environmental conditions.

One of the principal limiting factors to profitability of a pig enterprise using sugar cane juice as the basal diet is the cost of the protein supplement. Two approaches have been investigated to combat this problem. The first is based on the report of Estrella et al (1986) (cited by Mena 1989) that the protein input (mainly soyabean meal) to pigs fed ad libitum cane juice during the finishing phase (76 to 105 kg) could be reduced to 180 g/animal/d without affecting growth rates (780 g/d with 180 g protein/d compared with 820 g/d with 360 g protein/d). Based on this data, the present recommendations of CIPAV for sugar cane juice feeding systems are that the protein allowance be set at 200 g/d and maintained constant throughout the growing-fattening phase (Sarria 1989).

The second approach aims to take advantage of the absence of fibre in sugar cane juice so as to be able to accomodate foliar sources of protein in the form of leaves harvested from forage crops, trees and water plants. Mena (1989) cited observations by Abreu et al that fresh leaves from both cassava and leucaena were consumed by pigs fed on cane juice and restricted amounts of protein supplement. Growth rates appeared to be reduced by leucaena but not by cassava leaves. One of the problems with leaves from tropical tree species is the presence of secondary plant compounds, chiefly phenolic substances, whose role is to protect the leaf from insect attack. Unfortunately, another characteristic of these substances is that they make the leaf unpalatable, especially for monogastric animals. Thus leaves of Gliricidia sepium , although readily eaten by ruminants, are not relished by either chickens or pigs.

Aquatic plant species, because of their growth habit, appear not to accumulate secondary plant compounds and therefore offer perhaps a greater potential than trees as a source of protein for monogastric animals. Of these species the water fern Azolla filiculoides, which grows in association with the blue-green alga Anabaena azollae, is perhaps the most promising from the point of view of ease of cultivation, productivity and nutritive value (Lumpkin and Plucknett 1982; Van Hove and López 1983).

The aims of the experiments to be described in this paper were to obtain data under commercial farm conditions concerning: (i) the management and productivity of Azolla as a protein crop; and (ii) its value as a partial replacement for soyabean meal in a sugar cane juice feeding system for pigs.

The experiments were carried out on the "Lucerna" farm situated near the town of Bugalagrande (latitude 3°N and longitude 76°E) Departamento Valle del Cauca. Height above sea level is 960 m, mean temperature 24°C (range 19 to 29°C) and mean rainfall 1100 mm. Relative humidity varies from 60 to 85% throughout the year.

Nine tanks were constructed each measuring 20 m long, 2.6 m wide and 0.7 m deep with a 2 m separation between each giving a total surface area of 468 m². They were sown with a culture of Azolla filiculoides of Brazilian origin which was growing on a commercial farm also situated in the Valley but at some 1500 m above sea level. Fertilization was with poultry litter at the rate of 10 g/m²/d. Water depth was maintained at 40 cm using river water. The amount added to compensate for evaporation and filtration corresponded to approximately 5% of the total volume daily. Each day 100 kg fresh weight of Azolla was harvested, corresponding to the production of one quarter of the area of three tanks. Thus there was an interval of three days before returning to harvest the same tanks.

Three dietary treatments were imposed on growing-fattening pigs receiving a basal diet of fresh sugar cane juice. These consisted of:

A homogeneous group of 13 weaner pigs was allocated to each treatment. The pens were adjacent to one another and of similar size. Statistical analysis was restricted to the liveweight data, using differences among animals within pens as the source of residual variation. The data were analysed separately over the growth phase (20 to 50 kg liveweight), the fattening phase (50 to 90 kg) and the overall period.

The weaner pigs weighed 20 kg on average at the start of the trial. The conventional protein supplemented was prepared on the farm and contained 90% soybean meal and 10% of a mineral-vitamin mixture. It was given as the first feed in the morning at approximately 7 am, followed by the azolla which had been harvested the day before and left to drain overnight. Fresh cane juice was extracted from the stalks of sugar cane grown commercially on the farm (some 300 ha are established on the farm for sale to the local sugar factory) using a 3-roll mill (capacity about 1 tonne cane stalk/hour), typically employed for production of "Panela" (non-crystallized brown sugar). Extraction rate averaged 50 kg of juice from 100 kg of cane stalk. The cane juice was given first at approximately 11 am (immediately after milling of the stalk) and again in the afternoon in quantities calculated to result in a slight residue the following morning. Precise control of the amount of juice offered and refused was not possible as the experimental groups had to be managed as a component of the overall commercial programme which involved some 200 animals all fed on the cane juice system. The mean intakes were estimated to be about 7 litres daily in the growth phase and 11 litres in the finishing phase. The pigs were weighed individually every 14 days and mean liveweight gains calculated from the regression coefficient of liveweight against time.

Estimates of the annual productivity of the Azolla, assuming the production during the first 150 days can be sustained, are given in Table 1.

Table 1: Estimated productivity of Azolla biomass based on actual amounts harvested during the 154 days of the trial from 1 June to 31 October 1989.

Total area of tanks (m²)	468
Azolla harvested daily (kg)
- Total amount fresh basis	100
- Total dry weight	5
- Protein in dry matter (%)	23
- Total protein daily (kg)	1.15
Estimated annual production (tonnes/ha)
- Dry biomass	39
- Protein	9.00

The recorded productivity of the Azolla during the 5 month period of the trial was high and within the range (6 to 9 tonnes protein/ha/year) reported by Lumpkin and Plucknett (1982).

Analysis of nitrogen, P, Ca and K in representative samples of the Azolla from the experiment shows that the recorded values are within the range reported in the literature (Table 2).

Table 2: Chemical composition of the Azolla

Analysis % of DM	Lucerna	Literature*

Nitrogen	3.8	2.0 - 5.3
P	0.7	0.2 - 1.6
Ca	1.7	0.5 - 1.7
K	1.8	0.3 - 6.0

Mean values for liveweight gain and feed intake are given in Tables 3, 4 and 5 for the growth, finishing and overall phases respectively.

Table 3: Mean values for growth rate, feed intake and feed conver-sion during the growing phase

		% protein replaced by Azolla
	Control	15	30	SE(Prob)

No of pigs	13	13	11
Liveweight (kg)
- Initial	25.3	23.0	21.2
- Final	53.7	52.8	51.6
- Daily gain	0.425	0.363	0.341	±0.019(0.01)
Length of period (d)	71	85	85
Feed intake (kg/d)
- Cane juice	7	7	7
- Protein supplement	0.5	0.425	0.341
- Azolla	-	2.6	5.2
- Dry matter	1.83	1.89	1.95
Conversion (DM basis)	4.3	5.2	5.7

Table 4: Mean values for growth rate, feed intake and feed conversion during the finishing phase

		% protein replaced by Azolla
	Control	15	30	SE(Prob)

No of pigs	13	13	11
Liveweight (kg)
- Initial	53.7	52.8	51.6
- Final	90.5	89.7	87.5
- Daily gain	0.540	0.589	0.568	±0.034(0.21)
Period (d)	67	69	69
Feed intake (kg/d)
- Cane juice	11	11	11
- Protein supplement	0.5	0.425	0.35
- Azolla	-	2.6	5.2
- Dry matter	2.65	2.71	2.77
Conversion (DM basis)	4.9	4.6	4.87

Table 5: Mean values for growth rate, feed intake and feed conversion during the overall period

		% protein replaced by Azola
	Control	15	30	SE(Prob)

No of pigs	13	13	11
Liveweight (kg)
- Initial	25.3	23.0	21.2
- Final	90.5	89.7	87.5
- Daily gain	0.482	0.475	0.454	±0.045(0.80)
Length of period (d)	138	154	154
Feed intake (kg/d)
- Cane juice	9.1	9.1	9.1
- Protein supplement	0.5	0.425	0.35
- Azolla	-	2.6	5.2
- Dry matter	2.27	2.33	2.39
Conversion (DM basis)	4.73	4.90	5.26

There were significant differences (P = 0.01) among groups of pigs receiving the experimental treatments during the growth phase (Table 3). Performance decreased as the amount of Azolla in the diet increased. These effects were reversed in the fininishing phase when there was a strong tendency (P = 0.2) for the pigs fed azolla to grow faster than on the control treatment (Table 4). The final result was that there were no differences in growth rate (P = 0.80) among treatment groups for the total period of the trial (Table 5).

It is understood that the differences attributable to the treatments are confounded with the differences attributable to pens since there were no replications of pens. However, the pens were of similar size and design and located together in the same part of the piggery. It seems reasonable to conclude that the observed differences among treatments probably were the result of the level of Azolla in the diet.

It is difficult to explain the contrasting differences in the growing and fattening phases. A reasonable hypothesis would be that the limiting factor to the use of fresh Azolla in the diet of pigs is its low nutrient density due to the extremely high moisture content (approximately 95%), and the inability of the young pigs to consume the required quantities. This was observed to be the case with fresh leaves from the tree Trichantera gigantea which were consumed in adequate amounts (i.e. to supply 200 g protein daily) by pregnant sows but not by growing pigs (C. Mejia, personal communication). It did not seem that this was the problem in the present experiment since the indicated amounts were consumed fully. However, it was observed that during the growing phase it was necessary to offer the Azolla in two portions daily while in the finishing period it was sufficient to feed it only once in the morning. More observations are necessary before this theory can be substantiated or rejected.

A possible imbalance of amino acids due to inclusion of Azolla would not appear to be the problem, since Azolla protein appears to have a better amino acid profile than soybean mean such that the combination of the two more closely resembles the balance required by the growing pig according to the recent studies of Wang and Fuller (1989) (Table 6).

More logical explanantions for the diferences in utilization efficiency of the Azolla according to the age (size) of the pig are that some period of adaptation is necessary to develop a microbial flora in the caecum capable of digesting efficiently the fibrous components of this plant. Alternatively, the older animal may masticate more thoroughly the plant material during eating which would facilitate access to the Azolla protein by the pig's gastric enzymes. The fact that performance tended to be better with 15% than with 30% replacement by Azolla protein supports this view.

Table 6: The balance of amino acids (as % of Lysine = 100) required by the growing pig (Wang and Fuller 1989)* compared with that supplied by soybean meal (control supplement) and combinations of soyabean meal and Azolla.

	Optimum*		% protein replaced by Azolla
		Control	15	30

Lysine	100	100	100	100
Met+cis	63	48	50	53
Threonine	72	61	63	65
Tryptophan	18	22	23	25
Valina	75	83	86	89
Isoleucine	60	90	89	88
Leucine	110	133	134	135
Phenylan+Tyrosine	120	139	141	143
Relation essential to non-essential AA	50:50	40:60	42:58	43:57

The preliminary data reported in this paper must be interpreted in the light of the limitations facing most animal experiments carried out on commercial farms, especially the difficulty of obtaining precise data on feed intake and being able to set up correctly designed trials with adequate replications. Despite this, the information obtained has served to stimulate interest in the growing and use of Azolla as a protein supplement. The net result is that the technology is already being applied on a number of farms in Colombia, with satisfactory results both from the biological and economic standpoint. More importantly, these on- farm activities are generating invaluable information concerning the practice of growing and utilization of this feed resource under varying environmental conditions.

This experiment was carried out as part of the requirements for the graduate thesis of the senior author. The authors acknowledge the contribution of of the management and workers of the Lucerna farm, and of the researchers in CIPAV, whose interest and collaboration made this work possible.

Lumpkin T A and Plucknett D L 1982 Azolla as a green manure; use and management in crop production. Series No15, pp230, Westview Press; Boulder, Colorado, USA

Mena A 1988 Sugar cane juice as animal feed: an overview. In:Sugarcane as Feed (Editors: R Sansoucy, G Aarts and T R Preston) FAO:Rome pp153-163

Sarria Patricia 1989 Produción de cerdos en Colombia con base en los derivados de la caña de azucar. In: La caña de azúcar en la alimentación animal (Editors: T R Preston and M Rosales). GEPLACEA:México (In press)

Van Hove C and López Y 1983 Fisiología de Azolla. In: Workshop on the assessment of Azolla use in Tropical Latin América. Chiclayo: Peru (mimeógrafo)

Wang T C and Fuller M F 1989 The optimum dietary amino acid pattern for growing pigs. 1. Experiments by amino acid deletion. British Journal of Nutrition 62:77-89