The possibility of using unicellular algae (Chlorella and Scenedesmus) as feed for cattle has been studied. Mixed algal culture was grown in a shallow polythene-lined pond and gave a recorded daily yield of 95 tonnes of algal suspension (packed cell volume 5-10 ml/litre) or 247 kg dry substances per hectare. The cost was about $1.25 (Tk. 50) per tonne of algal suspension production. Dried algal cells contained 613 g crude protein (N x 6.25) and 155 g fibre per kg DM. In a 120 d feeding trial 8 growing cattle (7 females and 1 male), of indigenous breed with mean initial live weight kg 146"9 kg, were fed ad libitum urea- molasses-straw and 2 kg/d wheat bran as basal diet. The treatments were 0.5 kg/d Til (sesame) oil cake per head in group I and ad libitum algal suspension in group II. The suspension was drunk at 10% of animal live weight. These animals received no other liquid (water).

Inclusion of algal suspension did not improve total metabolizable energy (ME) or crude protein (N x 6.25) intake but increased daily gain, although insignificantly (P > 0.05) from 399 g for the oil cake treatment to 458 g in the algae group. The feed conversion efficiencies were 6.2 and 7.4 g live weight gain per MJ ME intake for the oil cake and algae groups, respectively. Crude fibre digestibility was significantly (P < 0.01) higher in the algae (81.1%) than the oil cake group (76.2%). For the 120 d feeding trial, the estimated net economic loss was $5.0 (Tk. 200)/animal on oil cake while there was a $14.4 (Tk. 576) profit/animal on algae.

Being a simple production technique of low cost and environmentally friendly, the present results justify more work on the subject.

One of the major constraints to livestock production in Bangladesh as well as most tropical, developing countries is shortage of protein (Preston and Leng 1987; Huque et al 1992; Tareque and Saadullah 1988). In Bangladesh, most of the available nutrients come from the by-products of crop-production. Straw contributes approximately 70% of the available dry matter (Rahman et al 1990). Oil cakes, brans and green grasses are the most common supplements used in Bangladesh (Rahman et al 1990). Often these supplements are relatively costly and may not be available under many conditions, which necessitates the search for other cheap sources of supplements which can correct the nutritional imbalances imposed by straw.

In the early fifties, Japanese and German workers explored the possibility of utilizing fast growing unicellular algae as a source of nutrients for humans and animals (Halama 1990). Of the different algal species, Chlorella and Scenedesmus are the most widely studied. Their protein content ranges from 50 to 60% of dry matter. Except for sulphur-containing amino acids (methionine and cystine), the essential amino acid content is favourable for the nutrition of farm animals (Halama 1990). Algae are also a rich source of carotene, vitamin C and K, and B-vitamins (Halama 1990). Because of a cellulosic cell membrane, Chlorella and Scenedesmus are not efficiently utilized by monogastric animals. Pregastric fermentation by microbes enables ruminants to utilize cellulose very efficiently. This work has been undertaken with the objective of utilizing algal suspension as feed for cattle.

Seven indigenous female, and one male, cattle approximately 22 months old, were used. At the onset of the trial, all animals were treated with antihelmentics and the overnight fasted weight recorded as their initial live weights. The animals were individually housed and fed. Feed, algal suspension and water were given twice daily and residual feed was measured the following morning.

The animals were randomly divided into two groups, with four in each. In addition to ad libitum supply of urea-molasses straw and 2 kg/d wheat bran, one group of animals received 0.5 kg/d Til (sesame) oil cake per head (oil cake group), while the other group received algal suspension ad libitum (algae group) (Table 1). Urea-molasses straw was prepared every alternate day by mixing straw with a solution of urea and molasses. Urea and molasses were added at the rate of 3% and 15%, respectively of straw dry matter. Fresh water was made available all the time for the oil cake fed animals, while the algae fed animals received ad libitum supply of algal suspension instead. The concentration of algae in the suspension usually ranged between 5 and 10 ml packed cell volume/litre. The chemical composition of the different feed ingredients is presented in Table 2.

Tabla 1: Composition of the experimental diets and quantities fed
	Oil cake	Algae
A. Urea-molasses-straw(UMS)	ad lib	ad lib
Composition of UMS (g)
Straw	820	820
Molasses	150	150
Urea	30	30
Total	1000	1000
B. Wheat bran (kg/d)	2.0	2.0
C. Algal suspension	-	ad libitum
D. Oil cake (kg/d)	0.5	-

Table 2: Chemical composition of the feed ingredients used in the formulation of the diets
	UMS	W bran	Oilcake	Algal susp
Dry matter, %	71.7	94.9	91.5	2.6
As % of dry matter
N x 6.25	8.3	16.0	25.1	61.3
Fibre	40.6	12.9	24.1	15.5
Ash	21.0	5.1	13.5	-

The algal suspension was produced in five artificial ponds in the Experimental Station. The artificial ponds (300L x 100W x 12D cm) were prepared by building a rectangular wall on a plane surface, using bricks or mud. This was then covered with polythene sheet of 340 (L) x 150 (W) cm. For the production of algal suspension, 15 litres algal inoculum (mixed culture of Chlorella and Scenedesmus, obtained from Bangladesh Council for Scientific and Industrial Research (BCSIR), Dhaka were mixed with 1 litre of matikalai (Vigna mungo) bran extract and added to 200 litres fresh clean water in the artificial pond. After 12 hours, 2 mg of ammonium phosphate were added to the culture as a source of N. However, similar amounts of urea can also be used instead of ammonium phosphate. Matikalai bran extract was prepared by overnight soaking of 100 g in 1 litre water, followed by filtration through two layers of cloth. Generally the algal suspension is ready for feeding after one week when packed cell volume ranges between 5 and 10 ml/litre. As the algal cells precipitate at the bottom, the culture needs to be stirred at least twice daily.

On the fifth week of the feeding trial, digestibility of the rations was measured, when in addition to the usual measurement of feed offered and refused, the faecal output over 24 hours of individual animals was also recorded.

The animals were weighed fortnightly before morning feeding. Daily gain was calculated as the slope of the regression of live weight versus time for each individual animal.

Samples of feed ingredients, refusals and faeces were analyzed for dry matter (DM), ash, N and acid detergent fibre. Dry matter was determined by drying a sample at 100 ?C for 48 hours and ash by ashing at 590 ?C to 600 ?C. N and fibre were determined as per the recommendation of AOAC (1984).

A simple "t" test was used for measuring the differences between means of each variate with appropriate standard error of differences (SED). A simple linear regression (y = a + bx) was used for measuring the liveweight gain.

ALGAE PRODUCTION: The experiment was conducted from January to April 1994. Under these conditions 200 litres of algal suspension, having PCV content of 5-10ml/litre, were produced in a 7 day period in each pond. This represents a daily production of approximately 95 tonnes algal suspension or 247 kg dry substances per hectare. This production rate is much higher than the reported yield of 25 kg dry substance observed in Scenedesmus culture (Boda 1990). For feeding four animals, it required on an average 50 litres of algal suspension daily which was obtained from five ponds. Algae were cultured in five ponds in such a way that at any time at least one pond had suspension ready to feed.

Apart from the environmental factors (eg: temperature, radiation intensity), inadequate or excess supply of nutrients (ie: matikalai extract, (NH₄) ₂PO₄ or urea) affected the algae production. The algal suspension usually turned brown (indicating dead cells) from the usual brilliant green colour whenever excessive amounts of matikalai bran extract were added. For maintaining the volume of algal suspension the required amounts of water to add depended on the evaporation rate. After being used for feeding, the algal culture can be re-established just by adding the necessary water to the residual algal cells and nutrient solution, as there is always enough algal cell left in the pond to restart.

Table 2 presents the chemical composition of the algal suspension. The suspension, as expected, contained very little dry matter (2.6 g/litre). The N x 6.25 content of 61.3% is much higher than the reported values of 450 to 490 g/kg DM (Halama 1990). The fibre content was 15.5%. However this is consistent with the total carbohydrate content of 16.0 to 20.0% in DM (Halama 1990).

The animals of the algae group were not given any drinking water. Instead the suspension was supplied ad libitum. There was no difficulty in introducing the algal suspension to the animals. Intakes steadily increased from approximately 9 litres daily at first to over 20 litres/d on the 8th fortnightly interval. Intake was closely related (r2 = 0.93) to live weights. For each kg increase in live weight, algal suspension intake increased by 0.222 (SE 0.026, P < 0.01) litres daily. Consumption of algal suspension was approximately 10% of live weight. From our observation it was found that the day to day variation of suspension intake was affected by ambient temperature and humidity. Generally on a hot dry day, intake increased and it decreased on a wet and cool day.

Considering the depreciation cost of pond construction materials (bricks and polythene), the prices of inputs used for the production of algal suspension (eg: matikalai, bran, urea or (NH₄) ₂PO₄) and labourers, it costs about $1.25 to make 1000 litre of algal suspension. Water cost was not included and all calculations were based on current market prices.

Dry matter intake from straw impregnated with urea and molasses is given in Table 4. Differences in straw intake were not significant (P>0.05) (4730 vs. 4660g/d). When expressed as a per cent of live weight, the straw dry matter intakes were 2.8 and 2.9%, respectively for the oil cake and algae-fed animals. In both groups, straw dry matter intake contributed over 70% (70% for oil cake group and 74% for the algae group) of the total DM intake.

Table 3: Live weights, daily gains, intake and feed conversion efficiencies in animals given urea-molasses straw either with oil cake or with algae for 120 days
Treatment	Oil cake	Algae	SED/Prob
No. of animals per treatment	4	4
Liveweight, kg
Initial #	150	140	6.61/NS
Final #	197	198	8.27/NS
Daily gain #	0.399	0.458	0.032/NS
Daily DM intake (g)
Urea-molasses-straw	4730	4660	728/NS
Wheat bran	1566	1566
Oil cake	435	-
Algal cells	-	31
Daily ME Intake (MJ)	64.2	61.6	1.2/NS
M/D (ME/DM, MJ/kg)	9.53	9.84
Feed conversion efficiency
(g live weight gain/MJ ME)	6.2	7.4
Daily N x 6.25 intake (g)	653	456	8.06/0.01

# Calculated from individual regression of live weight on time. Calculated from digestible organic matter apparently fermented in the rumen, assuming 15.6 MJ/kg DOMR (ARC 1980)

The initial and final weights and daily gains are presented in Table 3. The initial weight was obtained in the morning after overnight fast and as a calculated initial weight, using the intercept at zero time of the regression of liveweight on time. There was no significant difference in growth rate due to treatment (P > 0.05). The maximum daily algal protein intake was estimated to be 33 g (assuming algal suspension intake of 20 litres, at 2.6% DM and 61.3% N x 6.25/DM), while the oil cake fed animals received approximately 108 g per head (assuming 25% N x 6.25 in DM from oil cake. From the present understanding of rumen fermentation (see ARC 1984) it would appear that the algae- fed animals must have had very efficient microbial protein production to support the protein requirement for their slightly higher growth rates. Another possibility is that the algae (Chlorella and Scenedesmus) served as rich sources of vitamins, minerals and essential amino acids (Halama 1990). This might have improved the efficiency of nutrient utilization in the rumen and/or post ruminally. Despite higher DM and N intake by the oil cake group, the tendency for higher growth rate in the algae fed animals poses questions like whether these standard requirements for protein bear any relationship with what an animal actually received at the tissue level to support bio-synthetic processes (eg: growth).

Feed conversion efficiencies are presented in Table 4. The conversion of ME to live weight was 6 and 7 g gain/MJ for the oil cake and algae-fed animals, respectively. The calculated energy densities were 9.5 and 9.8 MJ/kg DM. Webster (1989) showed that with a poor quality hay diet (M/D of 8), Frisian x Hereford cross steers achieved 4 g gain/MJ ME. Silva et al (1989) similarly showed a live weight gain of 4.6 g/MJ ME on an ammoniated straw diet (M/D of 7). However, Saadullah (1984) reported a live weight gain of 14 g/MJ ME on an untreated straw diet (M/D of 6) supplemented with fishmeal. This high feed conversion efficiency on the straw diet has been attributed to more efficient utilization of nutrients due to a more appropriate balance (acetogenic:glucogenic ratio) aided by fish meal supplementation (Leng 1990).

Digestibility coefficients of the two diets are presented in Table 5. Both DM and OM digestibilities were similar on the two diets. However, fibre digestibility was significantly (P<0.01) higher in the algae-fed animals.

Table 4: Digestibility (%) of the dietary nutrients in the two diets
Treatments	Oil cake	Algae	SED/Prob
Dry matter	68.5	69.6	0.841/NS
Organic matter	70.7	71.7	0.779/NS
Crude fibre	76.2	81.1	1.29/0.01

Higher fibre digestibility in the algae-fed animals may have been due to higher rumen cellulolytic activity, but how exactly algae might improve the cellulolytic activity in the rumen is yet to be understood.

Feed cost is shown in Table 5. Total feed costs were $64.9 (Tk. 2594) and $54.3 (Tk. 2172), respectively for the oil cake and algae-fed animals. Considering growth rates of 0.399 and 0.458 kg/d (See Table 3) the oil cake and algae group gained 45 and 55 kg live weight, respectively in 120 days. Assuming a price of $1.25 (Tk. 50) for each kg live weight, the former group encountered a total loss of $5.0 (Tk. 200) while the latter earned a profit of $14.4 (Tk. 576) per animal. It is worth mentioning that "on-foot" price of an animal depends not only on its weight, but to a large extent on age, conformation, colour and skin glossiness, which can collectively be referred to as "face value". The algae had better "face value" than the oil cake fed animals. Considering all these factors under the present experimental conditions, supplementing with an algae suspension would obviously be more profitable than supplementing with oil cake.

Although the mechanism has not been understood yet, algal suspension appeared to improve the balance of nutrients in a straw-based diet and thus increased the efficiency of conversion of feed to products (growth). Nitrogen deficient straw being the main source of nutrients for ruminants in Bangladesh (Tareque and Saadullah 1988), the introduction of algal suspension in the feeding system would certainly help economic livestock production. Many livestock farmers, particularly in the urban and suburban areas, raise their animals absolutely on straw and concentrate with either very little or no green grasses. This system of feeding is often associated with infertility, night blindness or even total blindness or other symptoms of vitamin A deficiency. Algae are a very rich source of carotene and algal suspension could be a potential source of vitamin A to combat such deficiencies. As a unicellular plant, algae use CO₂ and emit O₂ during photosynthesis and thus help in reducing environmental pollution.

Table 5: Economic analysis of two diets (based on current market prices)
	Oil cake			Algae
Ingredients	Price	kg	Tk	kg	Tk
	(Tk/kg)
Straw	1.00	5.56	5.56	5.48	5.48
Wheat Bran	5.50	1.8	9.90	1.8	9.90
Oil cake	7.00	0.5	3.50
Algae	0.05			20	1.0
Molasses	2.20	0.825	1.82	0.822	1.80
Urea	5.0		0.166		0.83
Feed cost
Tk/d			21.6		18.1
Tk x120d			2594		2172
Value weight gain in 120 days @ 50Tk/kg			2394		2748
Net gain (Tk)			-200		576

Feeding algal suspension, rather than oil cake, appears to have increased the fibre digestibility and feed efficiency. To understand how algal suspension has improved feed utilization, it is essential to study the effect of algal suspension feeding on rumen fermentation and microbial production. Similar studies should also be conducted in milking animals.

(Received 20 October 1994)