Livestock Research for Rural Development 14 (2) 2002

Blocks or cakes of urea-molasses as supplements for Sindhi x Yellow growing cattle fed rice straw and cut grass or cassava foliage

Ho Quang Do, Vo Van Son  and T R Preston*

College of Agriculture, Cantho University, Cantho, Vietnam
* University of Tropical Agriculture, Phnom Penh, Cambodia


Nine growing cross-bred heifers (Sindhi X Yellow cattle) of 162 kg, receiving a basal diet of ad libitum rice straw were allocated to three treatments given as supplements. These were: a urea-molasses mixture (10% urea) prepared as a soft cake and offered at 500g/head/day plus fresh grass at 3 kg/100 kg liveweight; a urea-molasses mixture (10% urea) prepared as a hard block offered ad libitum plus fresh grass at 3 kg/100 kg liveweight; a urea-molasses mixture (10% urea) as a soft cake offered at 500 g/head/day plus fresh cassava foliage at 3 kg/100 kg liveweight.

Intake of rice straw and of total dry matter were highest on  the combination of soft urea-molasses cake and cassava foliage supplements. The cattle ate all the soft cake that was offered (500 g/day) but those offered the hard block ate only  317g/day.  Growth rates were highest with the soft cake and cassava foliage supplement (270 g/day) followed by the soft cake and grass  (190 g/day) and hard block and grass (160 g/day).

 Key words: Cattle, urea, blocks, cakes, feed intake, rice straw, growth


Vietnam grows over 6 million ha of rice annually and it is estimated that this yields around 18 million tonnes of rice straw. This residue is the most abundant feed for ruminant animals in Vietnam, especially during the dry season. Many methods have been proposed for improving the nutritive value of rice straw, usually by some treatment involving the use of urea or ammonia (see review by Nguyen Trach 1998).  Incorporating urea in a hard block based on molasses and rice bran, with lime or cement as hardening agent, was proposed by Leng (1984) and popularised in many countries by the Feed Resources Group of FAO (Sansoucy 1986). Positive effects of this technology to improve use of rice straw by growing heifers were reported by Bui Xuan An et al (1992).  

Attempts to feed the hard block to swamp buffaloes in the Mekong delta were not successful as the animals would not consume them (Nguyen Van Thu et al 1993). Nguyen Phuc Tien and Preston (1998) observed the same phenomenon with swamp buffaloes exposed to one hour  of work daily driving a sugar cane crusher; by contrast, the same block was consumed avidly by native Yellow cattle on the same work schedule.  The solution to the intake problem, reported by Nguyen Van Thu et al (1993),  was to prepare the urea-rice bran-molasses mixture as a soft cake and, where necessary, to force-feed the mixture using a "bamboo pipe". 

There are few reports comparing the different methods of incorporating urea in rice straw diets and none comparing the hard "block" versus the soft "cake" (Nguyen Xuan Trach 1998).  The following experiment was designed to compare two methods of supplying the urea: comparing the hard "block" versus the soft "cake" and two forage supplements: ‘’Grass ‘’ versus ‘’ Cassava foliage’’

Material and methods

Location, animals and treatments

The trial was carried out on the Song Hau farm in Omon District, Cantho Province. Nine cross-bred (Sindhi x Yellow) heifers (initial weight 162 ± 9 kg) were housed in individual stalls and offered a basal diet of ad libitum rice straw. They were allocated to one of the following supplements :in a completely random design: :

·        Urea in a hard block + fresh grass

·        Urea in a soft cake + fresh grass

·        Urea in a soft cake + cassava foliage

Feeding system

The rice straw was purchased in Omon District, Cantho Provine. Fresh grass and fresh cassava foliage were purchased every day from farmers. The rice straw was offered ad libitum, fresh quantities being given morning and afternoon to ensure there was a residue of at least 0.5 kg.  The grass (mainly para grass, Bracchiaria decumbens) and foliage (leaf, petiole and soft green stems) from cassava plants were given fresh in a single feed at a level of 3 kg/head/day.   The hard block was offered ad libitum.  In the case of the soft cakes, one (250 g) was offered twice daily, in the  morning and afternoon. 

Table 1: Composition (air-dry basis) of the hard block and the soft cake


Soft cake

Hard block




Rice bran



Coconut meal















Bone meal






The soft cake was made by mixing first the urea, salt, coconut meal and rice bran. The molasses was then added, mixed and 1 kg of the mixture put into a box and pressed. For the hard block, the bone meal and cement were added to the rice bran, mixed together. The molasses was then added. A slurry was made of the lime, clay, salt and  water and this was then mixed with the dry ingredients.  The final mixture (lots of 2 kg) was pressed into a container and allowed to set in the shade for one week before being fed.


The cattle were weighed on two consecutive two days at 15 day intervals.  Intakes of rice straw, grass and the soft cake were recorded every day. The hard block was weighed when first offered to the animals and again when it was almost fully consumed, after which it was replaced with a new block.  The rice straw, cassava foliage and grass were sampled every month and analysed for dry matter (48 hours in a forced air oven at 100 °C).

Statistical analysis

Liveweight gain for individual animals was estimated from the linear regression of liveweight on days in the trial. These data and those for feed intake were analysed by the ANOVA option of the Minitab software package (Version 12). The sources of variation were treatments and error.

Results and discussion

Feed intake

All the cake offered (500 g/head/day) was consumed while of the hard block, only 317 g/day was eaten. These findings are similar to those reported by Ho Quang Do et al (1999). Intake of rice straw was higher (P=0.04) for the supplements of soft cake versus hard block and for cassava foliage versus grass (P= 0.007).

Table 2: Mean values of liveweight, feed intake and conversion of  Sindhi*Yellow cattle fed rice straw and urea and forage supplements


Soft cake + grass

Hard block + grass

Soft cake + Cassava foliage


Liveweight, kg











Daily gain





Feed DM intake, kg/day

Rice straw





Grass /cassava





Block or cake#















Feed DM conversion





# Dry matter (%); Soft cake 88.4; Hard block 94.9; 

Growth rate

Highest growth rate (P=0.002) was recorded on the combination of the soft cake and the cassava foliage (270 g/day), followed by the soft cake and grass (190 g/day) with poorest results on the hard block and grass (160 g/day). The advantages of the soft cake over the hard block confirm the earlier findings of Ho Quang Do et al (1999) and appear to reflect the higher intake of urea and other nutrients on the former.

The advantages of fresh cassava foliage as a protein supplement were first demonstrated by Ffoulkes and Preston (1978),  who showed that it supported the same growth rate and feed conversion as soya bean meal in cattle fattened on liquid molasses-urea as the basal diet. Cassava hay, made by sun-drying the fresh foliage (Wanapat et al 1999), was used to replace part of the concentrate fed to Holstein*Zebu dairy cows with no loss in milk production (Wanapat et al 2000a,b).  Similarly, in lactating goats,  milk production was unchanged when cassava leaf meal replaced cottonseed cake as the protein supplement. Supplementing rice straw with fresh cassava foliage increased the intake of straw and the growth rate of local (Yellow) cattle in Cambodia (Seng Mom et al 2001). These reports and the results of the present experiment confirm that cassava foliage fed fresh, after sun-drying or as a leaf meal, can replace conventional protein meals as a source of bypass protein in diets for ruminants.


Replacing grass with fresh cassava foliage as a supplement for cattle fed rice straw and a urea-molasses mixture increased the growth rate by 40%.


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Received 25 July 2001

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