Seasonal growth in rabbits fed wheat and maize bran with tropical forages

Brans are readily available as an agro-industrial byproduct in the tropics: wheat bran commercially and maize bran in rural households. Rabbits fed a mixture of locally available forages were used to compare the efficacy of fattening with wheat bran, maize bran, a mixture of wheat and maize bran and a commercially available rabbit feed. Trials were undertaken in both the hotter rainy season and the cooler dry season.

Mortality and average daily gain (ADG) both indicated that the use of brans was not effective in the rainy season. In the dry season, however, the mixture of maize and wheat bran compared favourably with the commercial feed with 8.3 % mortality and 17.6 g ADG. Mortalities were especially high in the maize treatments in both seasons, 25 % in the cool season and 41.7 % in the rainy season. A toxicity effect from fungus infected maize bran is suspected.

Rabbits in the tropics are only rarely raised on a large commercial scale in which high-cost inputs such as specifically formulated pellets can be justified. Availability, transport and purchasing costs exclude the economic viability of using these feed sources in most situations. The small backyard rabbitry therefore depends on local resources such as forages and agricultural byproducts such as brans, both of which can be collected locally.

According to the NRC (1977) tables, growing rabbits require a minimum of 16% crude protein and 65% total digestible nutrients (TDN). According to the same publication, average wheat bran values satisfy the crude protein requirement but not the TDN minimum. For maize bran there is no published information for rabbits.

Ambient temperature affects appetite in rabbits which in turn reduces growth during warm seasons (Maetens and de Groote 1990; Prud'hon 1976). This has been shown particularly for low quality diets such as those based on brans (Muir and Massaete 1991). Most studies have shown that growth rates in high temperature, low intake situations can be increased by increasing the concentration of the digestible nutrients in the feed (Borgida and Duperray 1992). Diets based on low nutrient density byproducts such as brans may therefore be less useful in tropical hot seasons and more useful in the cooler seasons.

This trial was undertaken to study the possibility of using wheat bran and, more importantly in the tropics, maize bran as a basal diet for growing rabbits. An effort was made to verify whether seasonal temperature differences affected the performance of the animals fed the lower quality agricultural byproducts.

Table 1: Crude protein (N*6.25) content of dietary components used during both experiments

Diet component	Crude protein %

Wheat bran	15.7
Maize bran	12.4
Commercial pellets	15.6
Clitoria ternatea	16.0
Medicago sativa	17.7
Leucaena leucocephala	23.0
Pennisetum purpureum	9.6
Oxigono delaguense	13.8
Peanut straw	11.4

Forty-eight recently weaned 6-week old rabbits of undetermined mixed races commonly used in Mozambican cuniculture were each offered equal amounts of seasonally available fresh forages and hay (see Table 1). The amount of forage offered was measured and only in the case of the peanut hay were the amounts corrected for wastage since relatively few losses occurred in the fresh green material. The animals were divided into groups of 6 females and 6 males which were assigned to four ad libitum basal diets consisting of:

No other supplementation or medication was used. Animals were allowed a 1 week adaptation period and thereafter weighed individually each week to calculate average daily gain (ADG). Mortality rates and reasons for deaths were registered. Animals were kept in the experiment until they attained an average weight of 2 kg, the normal commercially acceptable weight, or up to 10 weeks, whichever came first. Carcass percentage of live weight was then estimated.

The experiment was carried out twice to test for seasonal effect. The first experiment took place during the cool dry season (July and August) when the mean daily temperature was 18.6oC and had a duration of 8 weeks. The second experiment took place during the hot rainy season (December through February) when mean daily temperature was 26.1oC and had a duration of 10 weeks.

During the cool dry season, weight gains were similar between the control and WM treatments (Table 2). The control diet with an ADG of 20.2 g/day was superior to the W and M treatments, both of which produced only 75% of the weight gain of the control. Low weight gains during week 6 reflect a widespread flare-up of coccidiosis.

Table 2: Average daily weight gains for rabbits fed either wheat bran, maize bran, a mixture of wheat and maize bran or commercial pellets along with various forages during the cool dry season

	wk1	wk2	wk3	wk4	wk5	wk6	wk7	wk8	Means*
	------------------------ g/day -------------------------

Pellets	25.0	17.0	29.5	16.4	23.5	8.9	22.6	18.5	20.2 a**
Wheat & Maize	19.3	23.1	21.7	19.3	18.0	8.6	17.6	13.1	17.6 ab
Wheat	17.9	18.6	20.8	13.7	22.6	2.7	15.2	10.4	15.2 b
Maize	18.6	14.9	22.6	12.2	16.4	11.3	15.2	9.8	15.1 b

*Coefficient of variation=21.6%
**Means within the same column followed by different letters differ (P<0.05) according to Duncan's Multiple Range Test.

Feed conversion was most efficient for the control diet although differences amongst the various treatments were not great (Table 3). The least efficient was the W diet which was 45% less efficient than the control. There were few differences for carcass percentages among the various treatments.

Table 3: Average daily dry matter consumed, conversion efficiencies of dietary components and carcass percentages during the cool dry season.

	Pellets	MW	Maize	Wheat

Intake, g/day
Maize bran	--	30.1	47.9	--
Wheat bran	--	33.7	--	57.4
Pellets	48.2	--	--	--
P. purpureum	9.4	10.2	9.1	10.5
C. ternatea	11.5	11.9	12.2	12.3
M. sativa	11.0	8.8	11.0	11.0
Peanut hay	51.1	51.7	51.7	49.9
DM intake	131.2	146.4	131.9	141.1
DM intake/gain	6.50	8.32	8.74	9.29
Carcass %	53.0	54.3	51.3	52.1

The WM diet supported slightly faster growth compared with W or M, but the differences were not significant (Table 4). The control treatment was superior to all others, averaging 201% of the M diet which had the lowest values. The generally lower gains during weeks 5 and 10 were due to widespread coccidiosis which was not treated with coccidiostat in order to simulate local conditions.

Feed conversion rates were poor for all the bran-based diets during the hot rainy season (Table 5). On average, they were 1.88 times the values of the control diet. Carcass percentages were likewise 7% lower, on average, for the bran-based diets.

Table 4. Average daily weight gains for rabbits fed either wheat bran, maize bran, a mixture of wheat and maize bran or commercial pellets along with various forages during the hot rainy season

	wk1	wk2	wk3	wk4	wk5	wk6	wk7	wk8	wk9	wk10	Mean*
	----------------------------g/day------------------------

Pellets	36.9	23.8	26.5	16.1	10.7	20.5	7.7	16.1	6.3	-1.8	16.3a**
Wheat/Maize	24.1	9.8	8.3	10.7	-0.3	6.8	12.5	17.6	12.2	11.9	11.4b
Wheat	26.2	11.0	5.4	7.4	-4.8	7.4	9.8	11.3	11.9	4.2	9.0b
Maize	26.2	6.0	5.1	2.7	7.0	6.5	6.8	9.8	7.4	3.6	8.1b

**Means within the same column followed by different letters differ (P<0.05) according to Duncan's Multiple Range Test.

Table 5: Average daily dry matter consumed, conversion efficiencies of dietary components and carcass percentages during the hot rainy season.

	Pellets	MW	Maize	Wheat

Feed DM intake, g/day
Maize bran	--	34.5	66.9	--
Wheat bran	--	35.7	--	71.1
Pellets	52.2	--	--	--
P. purpureum	14.4	14.4	12.4	13.3
C. ternatea	1.7	1.7	1.7	1.7
M. sativa	1.2	1.2	1.2	1.2
Leucaena	42.5	37.8	37.9	37.1
O. delaguense	5.1	5.1	5.1	5.1
DM intake	117.1	130.4	125.2	129.5
DM intake/gain	7.18	11.4	15.5	14.4
Carcass %	47.3	45.2	43.4	43.3

Overall average daily DM ingested was higher (137 g/day) and conversion efficiency better (8.2 g DM intake/g weight gained) in the dry season than in the hotter rainy season (126 g/day and 12.0 g DM intake/g weight gained). This decrease in intake parallels an overall lower ADG in the rainy season (11.2 g/day) compared with the cooler dry season (17.0 g/day).

Table 6: Mortality rates per treatment in each season

	Dry season	Wet Season

	-----------%----------
Pellets	0.0	0.0
Wheat/Maize Bran	8.3	25.0
Wheat Bran	8.3	41.7
Maize Bran	25.0	41.7

Since the mortality rate for the control treatment was zero during both seasons, it should be safe to conclude that mortality in the other treatments was due to inadequate nutrition resulting from poor diets (Table 6). The W and B treatments both had unacceptably high mortalities in the rainy season, due mainly to coccidiosis and suspected fungal intoxication in the maize bran. During the dry season, however, the W animals suffered only 33 % the mortalities of the M treatment, indicating that animals in the latter treatment were either weaker and less able to resist disease or there was a toxicity problem with the bran.

The results of these trials indicate that brans, especially a mixture of wheat and maize bran, can be successfully used in place of the locally produced pelleted feed, at least during the cool dry season. Since prices of brans hover at approximately 17% that of the pellets, by weight, the use of wheat brans or mixtures of wheat and maize brans appears to be economically attractive during the cooler dry season. Low intake associated with a probably low digetibility limit the effective use of brans in the hotter rainy season.

The economic loss due to mortality may also make the use of brans unviable during the hotter rainy season. Further studies should be carried out on the maize brans to determine if there is a toxicity problem. Maize brans in southern Mozambique are extracted after a soaking process that leaves them vulnerable to fungal growth if not immediately dried, especially in hotter weather.