Molasses-urea block (MUB) and Acacia mangium as supplements for crossbred heifers fed poor quality forages

Molasses-urea block (MUB) and Acacia mangium as supplements for crossbred heifers fed poor quality forages

In the first experiment, twenty four crossbred heifers, given forages of low nutritive value, were divided equally into 4 groups with different supplements: C1, 1 kg/d concentrate; MUB, 1 kg/d concentrate + 0.5 kg/d MUB; AM, 1 kg/d concentrate + fresh Acacia mangium leaves (2 kg/100 kg LW); AMMUB, 0.5 kg/d MUB + fresh Acacia mangium leaves (2 kg/100 kg LW). The experiment period was 90 days. DM intakes were 5.08, 6.21, 5.61, and 5.49 kg/d, and live weight gains were: 107, 340, 185, 236 g/d, for treatments C, MUB, AM and AMUB, respectively.

In experiment 2 a rumen-fistulated cow was fed 3 diets in turn: C, rice straw; MUB, rice straw + 0.5 kg/d MUB; AM rice, straw + fresh Acacia mangium leaves (2kg/100 kg LW). Rate of disappearance of rice straw increased 16-17% with MUB supplementation. There was no apparent effect of the Acacia mangium leaves.

KEY WORDS: Rice straw, Acacia mangium, rumen in sacco digestibility, rumen ecosystem, cattle, molasses-urea, blocks, growth

The basal diet of most of the cattle and buffaloes in Vietnam is based on agro-industrial residues, roadside grass or grazing on boundaries between crops. These diets are imbalanced in nutritional value and variable according to seasons.

In order to develop a sustainable ruminant production system in Vietnam, efforts are directed to making the best use of local feed resources by adjusting the production system according to the local conditions. The use of appropriate supplements is a fundamental component of the feeding strategy in order to balance nutrients at the level of the rumen and of the animal (Preston and Leng 1987).

The multi-nutritional block (MUB) based on molasses and urea is being introduced and used in many Asian countries (Leng and Preston 1983). It is easy to make, of low cost, uses local resources and is safe to feed.

Acacia mangium, a leguminous tree, has been planted on thousands of hectares in Vietnam. It produces abundant foliage especially in the dry season (Ngo and Nguyen 1991).

# The effect on performance of growing crossbred cattle of using MUB and Acacia mangium leaves as supplements to a basal diet derived, according to availability, from native grasses, sugarcane tops, guinea grass silage and rice straw given ad libitum.

# The effects of the supplements on the rumen ecosystem as measured by the rates of degradability of standard fibre sources.

24 crossbred Holstein-Sindhi heifers (170 kg liveweight, 18-21 months of age) were divided into four treatment groups and fed the same basal diet (native grasses and molasses given in restricted amounts; sugarcane tops, guinea grass silage and rice straw given ad libitum, according to availability). The experimental period was 90 days in the dry season. The treatments were:

C: 1 kg/d concentrate mixture
MUB: 1 kg/d concentrate + 0.5 kg/d MUB
AM: 1 kg/d concentrate + 2 kg/100 kg liveweight of fresh Acacia mangium leaves
AMMUB: 0.5 kg/d MUB + 2 kg/100 kg liveweight of Acacia mangium leaves

The Acacia mangium leaves were harvested by hand, wilted in the shade for 24 hr then chopped into 10-15 cm pieces before feeding to the animals (NB: Acceptance of the fresh leaves was low, but improved when the leaves were wilted for 24hr). The chemical composition (AOAC 1970) of the MUB is shown in Table 1 and of the rest of the feed resources in Table 2. The cattle were weighed every 14 days and records kept of feed intake.

A Sindi-local breed (Chinese yellow) heifer of 226 kg liveweight and 30 months of age was fitted with a rumen cannula. It was given the following three diets in consecutive periods of 14 days, the measurements of degradability in the rumen of standard fibre sources being made over the last 2 days of each period.

RS: Rice straw ad libitum
RSMUB: Rice straw ad libitum + 0.5 kg/d MUB (10% urea)
AM: Rice straw ad libitum + 2 kg/100 kg liveweight of fresh Acacia mangium leaves

Rice straw was used as the test feed to determine the efficacy of the rumen ecosystem to digest dry matter, organic matter and fibre. The nylon bag technique described by Orskov et al (1980) was used. There were four replicates of rice straw during the incubation for each of the three diets fed to the host animal.

Table1: Composition (%) of the MUB used in the two experiments

	Ingredients	Exp.1	Exp.2

	Urea	10	10
	Molasses	35	35
	Rice bran	29	-
	Peanut husks	-	30
	Lime	10	9
	Bentonite	10	10
	Salt	5	5
	Trace minerals	1	1

Table 2: Checmical composition of feeds used in experiment 1

		% in DM
Feed	DM	N x 6.25	Crude fibre


Sugarcane tops	39.0	6.99	37.1
Native grasses	36.1	8.57	37.0
Guinea grass silage	53.6	4.8	42.5
Rice straw	53.7	5.84	39.9
Molasses	69.3	5.59	0.23
Concentrate	92.0	16.5	12.1
Acacia foliage	29.7	17.5	44.8

Table 3: Chemical composition of the feeds used in experiment 2

Feed	DM			% in DM
		N x 6.25	Fibre	E Extract	Ash

Rice straw	87.7	4.06	50.1	1.06	10.9
Acacia leaves	30.0	16.7	55.3	5.97	4.82

There was an indication that intake of the basal feed (the low- nutritive value component of the diet) was higher when MUB was given. Only some 65% of the amounts offered of Acacia mangium leaves was consumed.

Table 4: Feed dry matter intakes in experiment 1

	C	C+MUB	AM	AMMUB

Feed DM intake,kg/d
Basal feed	4.19	4.96	4.07	4.63
Total diet	5.08	6.21	5.61	5.49

Table 5: Mean value for liveweights and gains in experiment 1

	C	MUB	Am	AMMUB	SEM(P)

Liveweight(kg)
Initial	169	170	170	169
Final	179	201	186	291
Gain/day*	109	340	185	237	±24(.001)

The MUB increased significantly the growth rate when concentrates were the only supplement, and the combination of MUB and Acacia mangium was better than that of concentrates alone or the combination of concentrates and Acacia mangium. This strongly indicates that (i) there was a deficiency of rumen ammonia when the basal diet was composed of grasses, cane tops and rice straw; and (ii) the unsuitability of the concentrate supplement (90% rice bran and 5% fish meal) for supplying ammonia for rumen microorganisms. The consistent positive effect of the MUB supplement on feed intake and on liveweight gain confirms many reports in the literature which indicate the value of this type of supplement when the basic diet is low in nitrogen (Leng and Preston 1984; Preston and Leng 1987; Sansoucy 1986).

The better results from the combination of MUB and Acacia mangium leaves than from concentrates justifies the strategy of supplementing the microbes (with MUB) and the animal (with the Acacia leaves).

The rates of degradability of dry matter, organic matter and crude fibre in the rice straw test feed were increased by supplementing the rice straw diet of the host animal with MUB. There was no apparent effect of the Acacia mangium leaves.

Table 6: Mean values for degradability of rice straw in the rumen of a fistulated heifer fed rice straw, straw + MUB and straw + Acacia mangium leaves

	DM	OM	Crude fibre

Degradability in 48h
Rice straw
Mean	41.29	39.00	46.96
SE	±2.4	±2.4	±2.8

Rice straw +MUB
Mean	47.9	45.7	54.9
SE	±3.2	±2.5	±2.8

Rice straw + Acacia mangium leaves
Mean	42.6	46.0	51.2
SE	±1.4	±1.3	±2.2

The results with MUB are similar to those reported by Perdok and Leng (1990). There are data in the literature, for similar basal diets, indicating beneficial effects on rumen fibre degradability when supplements of fresh grass (Guttierrez and Elliott 1981) or leucaena leaves were given. The fact that this was not observed in experiment 2 may be because of the low rumen degradability of both the dry matter and the nitrogen in fresh Acacia mangium leaves (Bui et al 1992).

As a supplement to rice straw for growing heifers, the combination of MUB and Acacia mangium leaves was better than that of concentrates or the combination of concentrates and Acacia mangium. This strongly indicates that (i) there was a deficiency of rumen ammonia when the basal diet was composed of grasses, cane tops and rice straw; and (ii) the unsuitability of the concentrate supplement (90% rice bran and 5% fish meal) for supplying ammonia for rumen microorganisms.

The authors acknowledge the financial support received from the TCP/FAO project and the SAREC project S/2 Vie 22. They are also highly appreciative of the co-operation of people of AnPhuoc state farm, farmers in GoVap district, SongBe Animal Husbandry Union and students of the Animal Husbandry and Veterinary Medicine Faculty of UAF.

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