Molasses-urea blocks as supplements for rabbits

* Rabbit Research Institute, Hanoi, Vietnam
** Animal Research Institute, Hanoi, Vietnam
*** CIPAV, Cali, AA7482, Colombia

A series of experiments were carried out to investigate the feasibility of replacing the traditional concentrate supplement in rabbit diets with multinutritional blocks based on molasses, cassava byproducts and up to 4% urea.

The results showed that multinutritional blocks based on molasses can be fed successfully as a partial substitute for cereal-based concentrates in diets for rabbits during all phases of production. No conclusions can be drawn about the usefulness of including urea in the blocks, other than that it does not seem to be harmful.

Cheeke and Raharjo (1988) in a review of rabbit production on tropical feed resources concluded that tropical grasses were unsuitable as the sole feed for rabbits due to their low digestibility (less than 10%). They considered that adequate supplementation was the principal limiting factor and proposed that the use of multinutritional blocks as developed by Leng (Preston and Leng 1987) could have a potential role in these feeding systems. The value of urea to create a more efficient ruminal environment for utilization of tropical forages in ruminants is widely appreciated (Preston and Leng 1987). We have not encountered references to the use of urea to enhance fibre digestion in tropical forages fed to livestock with hind gut fermentation capability, other than a personal communication (Herrera V H 1990) that horses with free access to molasses suffered cases of colic which was not a problem when the molasses contained 10% urea.

This study had as the principal aim the evaluation of multinutritional blocks as supplements to a basal diet of elephant grass (Pennisetum purpureum). Studies of the effect of including urea in the blocks were made on the basis of the hypothesis that this might enhance rate of fibre digestion in the caecum which in turn could lead to increased intake and performance.

Crossbred rabbits (New Zealand x Vietnamese) were used for this study. These animals were kept in cages (5 growing rabbits or one doe in a cage of 0.5 m²) in which there was an automatic drinking system. Fresh elephant grass (Pennisetum purpureum) was harvested daily and supplied ad libitum. The multinutritional blocks were mixed by hand and allowed to set in earthenware bowls. The materials used are shown in Table 1. The blocks, the concentrate supplement and the grass were analyzed for dry matter, crude protein (N x 6.25), fibre, ether extract and ash. The rabbits were weighed early in the morning before feeding. Feed intakes were recorded daily.

Table 1: Composition of blocks (%)

Ingredient	B1	B2	B3	B4

Molasses	50	50	50	50
Rice bran	13	13	8	11
Bagasse pith	30	20	20	30
Cassava leaf meal	-	10	15	-
Lime	5	5	5	5
Salt	2	2	2	2
Cassava root meal	-	-	-	2

The following five treatments (control and four mixtures of block) were compared:

Experimental: Blocks of different composition (B1, B2, B3, B4) (see Table 1 ) and elephant grass ad libitum.

The growth rates with only blocks and grass were in general inferior (P<0.001) to those with conventional concentrate (Table 2). Only in the case of the block with 10% cassava leaf meal and 13% rice bran (B2) was performance close to that of the control. It was decided therefore to test different amounts of concentrate along with the blocks.


Table 2: Performance (from 45 - 75 days) of growing rabbits given conventional concentrate feed or multinutritional blocks plus grass ad libitum (5 cages of 5 rabbits/treatment)

	Control	B1	B2	B3	B4

Live weight (g)
Initial	920±36	918±38	920±36.1	957±20	940±15.8
Final	1450±58.7	1200±39.6	1369±55.5	1300±33.4	1222±34.4

Daily gain(g/d)	17.5	9.4	15.0	11.4	9.4
	SE±1.09 (P<0.001)

The composition of the block used in this trial was 50% "C" molasses, 20% bagasse pith (from sugar factory), 5% cassava leaf meal, 5% cassava root meal, 9% rice bran, 4% groundnut cake, 2% salt, and 5% lime. The concentrate composition was 23% rice bran, 20% broken rice, 33% maize, 2% fish meal, 16% groundnut cake, 5% cassava root meal, and 1% mineral premix.

Table 3: Performance (from 30 to 70 days) of growing rabbits given different proportions of concentrate feed:molasses blocks and grass ad libitum (5 cages of 5 rabbits)

	Percentage of block
	0	30	40	50	60

Live weight (g)
Initial	445±5	450±7.9	440±5.9	430±7.3	440±5.9
Final	1445±15	1325±26	1382±13.9	1190±11	1170±10.6
Daily gain (g)	22.2	19.4	20.9	17.0	16.2
	SE±0.28 (P<0.001)
Feed intake (g/d)
Block	-	22.2	32	35	40.4
Concentrate	79	51.6	48.1	35	27
Elephant grass	123	118	122	123	123
Total DM	92	83	88	78	76
Conversion (kg feed/kg gain)	4.1	4.3	4.2	4.6	4.7

Performance was inferior for the treatments containing the multinutritional blocks (Table 3); however, the difference (10-20% poorer growth rate) although significant (P<0.001) was less marked than in Experiment 1.

The next trial examined the effect of including urea in the block and giving this as the only supplement to grass for growing rabbits. The composition of the different blocks is in Table 4 and the results are in Table 5.

Table 5: Performance (from 30 to 75 days) of growing rabbits given blocks with different levels of urea, a concentrate supplement and grass ad libitum (4 cages of 5 rabbits).

	Percentage of urea
	0	2	4	Control

Live weight (g):
Initial	590±3.5	595±3.8	590±6.4	590±6.5
Final	1480±22	1420±11	1520±15	1620±69
Daily gain (g/d)	19.8±0.52	18.3±0.31	20.7±0.26	22.9±1.5

	SE±0.82 (P=0.003)
Feed intake (g/d):
Block	32	30	31	--
Concentrate	48	45	46	80
Elephant grass	178	162	145	161
Total DM	94.5	88	87	96
Conversion (kg feed DM/kg gain)	4.8	4.8	4.2	4.3

The blocks were fed ad libitum along with concentrates (40% block: 60% concentrate).

Performance was better (Table 5) on the control treatment (P=0.003). However, in practical terms, the level of performance was acceptable on all the multinutritional block treatments, and this diet was more economical. There appeared to be no advantage from including urea in the block. There were no indications of toxicity on any of the treatments.

Blocks were made with 0, 2, and 4% urea and fed along with concentrates (30% block:70% concentrate) and grass (ad libitum) from day 10 of pregnancy to end (30 d) of lactation. The results for the 30 days of lactation are in Table 6.

Table 6: Performance of lactating rabbits given access to molasses blocks x with from 0 to 4% urea (10 rabbits per treatment)

	Control	0% urea	2% urea	4% urea

Numbers alive
Birth	5.2±0.52	5.2±0.61	5.0±0.35	4.8±0.42
Weaning	4.4±0.36	5.0±0.54	4.4±0.23	4.4±0.32
Weight (g)
At birth	50.5±0.81	49.0±1.9	45.3±1.6	55.0±2.0
At weaning	422±8.1	434±13	428±7.1	475±10

	SE±9.3 (P=0.001)
Weight of doe(g):
10 d> mating	3230±131	3140±95	3110±93	3197±62
Weaning	2530±88	2533±85	2525±72	2530±46
Loss (mating to weaning)	700±74	606±29	585±68	667±42

	SE±54 (P=0.41)
Feed intake during lactation (g/d):
Block	--	40	35	43
Concentrate	166	90	82	100
Elephant grass	400	433	370	277
Total DM	210	179	158	165
Conversion**	5.45	3.44	3.65	3.47

* The block and concentrate compositions were the same as in the experiment with growing rabbits.
** Conversion (kg feed DM/kg gain of progeny) was calculated after correcting for weight loss of doe during lactation.

There was a suggestion that litter weights were heavier on the diet with the blocks containing 4% urea; and that weight losses during pregnancy and lactation were less for does on all the block diets compared with the concentrate control.

This study was carried out with financial support from the FAO TCP Project TCP/VIE/8954 and the Swedish Agency for Research Collaboration with Developing Countries (SAREC) (Project: S/2 VIE 22).

Cheeke P R and Raharjo C 1988 Evaluación de forrajes tropicales y subproductos agrícolas como alimento para conejos. In: Sistemas Intensivos para la Producción Animal y de Energía Renovable con Recursos Tropicales (Editors: T R Preston and M Rosales) CIPAV: Cali. Tomo II pp33-42.

Preston T R and Leng R A 1987 Matching Ruminant Production Systems with Available Resources in the Tropics and Subtropics PENAMBUL Books Ltd: Armidale NSW, Australia

Table 4: Composition of blocks containing urea.

	Urea level (%)
Ingredient	0	2	4

Molasses	50	50	50
Rice bran	10	10	10
Bagasse pith	20	20	20
Cassava leaf meal	5	5	5
Lime	5	5	5
Salt	2	2	2
Urea	0	2	4
Cassava root meal	4	6	4
Groundnut cake	4	--	--