The Effect of Partial Replacement of Soybean Meal with Gliricidia Leaf Meal on the Performance and Organ Weights of Weaner Rabbits in the Tropics
In an experiment to determine the effect of feeding
graded levels of Gliricidia sepium Leaf Meal (GLM) on the performance
and organ weights of rabbits, 25 weaner rabbits, 5-6 weeks old, were randomly
allotted to 5 dietary treatments containing 0% (control), 5, 10, 15 and
20% GLM with 5 rabbits per treatment in a completely randomised design.
Each rabbit constituted a replicate. The rabbits were housed individually
in wire hutches in a spacious house and were given weighed quantities
of feed daily and unlimited access to clean drinking water for eight weeks.
The inclusion of GLM in the diets of the rabbits had no significant effect
on body weight gain, feed intake nor on feed conversion ratio of the rabbits.
However, significant reductions were observed in cost of feed kg-1
and in cost of producing a kg of meat as the level of GLM in the diets
was increased. Heart and lung weights were unaffected by dietary treatments
while kidney and liver weights were significantly higher in the 15 and
20% GLM groups than in the control 0, 5 and 10% GLM groups. It was concluded
that although incorporation of GLM even up to 20% level in the diets of
weaner rabbits does not significantly reduce tissue synthesis in the rabbits,
however, there is significant reduction in the cost of feeding weaner
rabbits in the tropics. This probably increases detoxification activities
in the liver and kidneys of rabbits when used at levels beyond 10%.
Most of the meat currently consumed in Nigeria, especially in the urban
and peri-urban regions, comes from the ruminant species (cattle, sheep
and goats), pigs and poultry, especially chickens. Together with fish,
they furnish the average Nigerian with only about 7.4 g of animal protein
per day (FAOSTAT, 2005), which is still far below the recommended animal
protein level of 35 g per required by an average adult human for proper
health. Efforts by governments, government agencies and scientists in
Nigeria at developing the livestock sub-sector to meet the country`s animal
protein needs have tended to concentrate on the traditional livestock
species - the ruminants, pigs and chickens and paid little attention to
the rabbit. With a population, in Nigeria, of only about 1.7 million (FAOSTAT,
2005), the rabbit is still a relatively unexplored livestock species in
Nigeria. Perhaps one of the reasons for the low level of rabbit production
in Nigeria is the high cost of commercial pellets (Odeyinka and Ijiyemi,
1997) which may constitute as much as 70% of the total cost of production
(Oruseibio, 2002; with the energy and protein-providing components of
finished feeds in Nigeria being the costliest. Although the rabbit is
known to have the ability to thrive on forages, which grow abundantly
in Nigeria especially in the high rainfall areas (Asuquo, 1997; Odeyinka
and Ijiyemi, 1997) its ability to digest dietary fibre is believed to
be less than one half as efficient as cattle (Slade and Hintz, 1969).
Nevertheless, rabbits can thrive on diets containing 14-25% crude fibre
(Adegbola et al., 1985; Asuquo, 1997). This ability, coupled with
its short generation interval, makes the rabbit a very useful animal in
meeting Nigeria`s animal protein needs in the short run.
Gliricidia sepium is a tropical tree legume, which grows abundantly
in the southern part of Nigeria. Previous records (Gohl, 1981; Adejumo
and Ademosun, 1985) have shown that the leaves contain as much as 20-30%
crude proteins and 15% crude fibre. The plant grows vigorously, is drought-resistant
and persistent, has good re-growth potentials and so can be used to provide
feed all year round (Atta-Krah and Sumberg, 1986) to rabbits thereby drastically
reducing the cost of production. However, cost considerations alone may
not be beneficial if performance indices such as growth, feed intake,
weight gains and livability are adversely affected.
This study was therefore carried out to ascertain the effect on body
weight, feed intake, feed conversion, feed costs and organ weights, resulting
from feeding diets in which soybean meal was replaced at varying levels
with Gliricidia Leaf Meal (GLM) to rabbits.
MATERIALS AND METHODS
This study was carried out from April to July, 2006 at the Delta State
University Teaching and Research Farm, Asaba Campus, Asaba in Nigeria
(6°14`N and 6° 49`E).
Test Ingredient and Experimental Diets
Fresh, young Gliricidia sepium leaves were harvested, dried under
shade for several days, milled to obtain Gliricidia Leaf Meal (GLM) and
incorporated into five rabbit diets in which soybean meal was replaced
with GLM at 0% (control), 5, 10, 15 and 20%. The diets (Table
1) were formulated to contain approximately 17% crude protein and
2340 kcal kg-1 Metabolizable Energy (ME). Dry samples of GLM
and the experimental diets were analysed for their proximate composition
using standard procedures by AOAC (1990).
Animals and Their Management
Twenty-five Dutch rabbits of mixed sexes, aged 5-6 weeks, were weighed
individually and randomly assigned to the five dietary treatments with
5 rabbits per treatment. Each rabbit was regarded as a replicate. The
rabbits were housed singly in cages in two rows of hutches. Each of the
cages measured approximately 70x60x54 cm. The hutches were raised approximately
80 cm from the floor in a house with 1 m high dwarf walls, which permitted
sufficient ventilation. The experimental diets and clean drinking water
were provided the rabbits ad libitum for 8 weeks.
||Composition of the experimental diets (g kg-1 DM)
|GLM = Gliricidia Leaf Meal
At the end of eight weeks, two rabbits chosen at random from each
treatment group were starved overnight, stunned, sacrificed by cervical
dislocation and dissected in accordance with guidelines of the World Rabbit
Science Association (WRSA). The carcasses were then eviscerated and the
vital internal organs carefully removed and weighed and expressed as percentages
of the dressed weight.
Data on body weight, feed intake, feed conversion and costs and the weights
of the major internal organs of the rabbits were taken.
Data collected were analysed by the one-way analysis of variance procedure
using the IRRISTAT for Windows (Version 5.0.) computer software. Significantly
different means were separated by the Duncan`s Multiple Range Test procedure
RESULTS AND DISCUSSION
The proximate composition of Gliricidia Leaf Meal (GLM) is
presented in Table 2. The values obtained fell within
the range of nutrients earlier reported for Gliricidia sepium in
the tropics by Göhl (1981), Chadhokar (1982) and Adejumo and Ademosun
(1983). Its protein content was, however, lower than those reported for
the forage by Herbert (1998) and Ifut and Inyang (2007) (19.30 and 25.63%,
respectively) while its crude fibre and ash contents were higher than
those reported by Herbert (1998) (19.00%) due, perhaps, to differences
in edaphic characteristics to which the plants were exposed and to possible
variations in plant age, processing procedures and climate.
Table 3 shows the energy and proximate composition
of the experimental diets, while the performance characteristics and feed
costs of the rabbits fed the experimental diets are presented in Table
4. The energy and proximate values of the diets fell within recommended
ranges of nutrients required by rabbits in the tropics for optimum growth
and performance (Aduku and Olukosi, 1990) (12-17% Crude Protein; 20-25%
fat; 10-20% Crude Fibre; 2.39-2.50 kcal g-1 Digestible Energy).
Although body weight gains and feed intake tended to decline as the level
of GLM in the diets was increased, which is a reflection of the increasing
levels of fibre in the diets, the differences were non-significant. The
body weight gains observed in this study are in agreement with the reports
of studies on rabbits in Nigeria by Omole (1982) and Aduku et al.
(1988) and are an indication that the use of up to 20% GLM in rabbit diets
does not adversely reduce tissue synthesis.
||Performance and feed costs of rabbits fed the experimental diets
Mean ± SEM)
|Within each row, means with the same superscripts are
not significantly different
||Organ weights of rabbits fed the experimental diets (Mean ± SEM)
|Within each row, means with the same superscripts are
not significantly different
Feed conversion ratio, though numerically higher for the 10, 15 and 20%
GLM diets when compared to the control treatment (Table
4), was not significantly affected by dietary treatments.
The economic indices showed significant reductions in cost kg-1
of feed and in cost kg-1 body weight gain. This implies that
inclusion of GLM at moderate levels of up to 20% can substantially reduce
feed costs without significantly reducing feed intake, feed conversion
and growth in rabbits.
Changes in the organ weights of the rabbits with variations in the level
of dietary GLM are shown in Table 5. Variations in the
heart and lung weights with dietary treatments were not significant whereas
the kidney and liver weights tended to increase as the proportion of GLM
in the diets increased. The weights of some internal organs like the liver
and kidney are commonly used in animal feeding experiments as evidences
of toxicity (Ahamefule et al., 2006). Bone (1979) reported that
increased metabolic rate of the organs in attempt to reduce toxic or anti-nutritional
factors in livestock feeds to non-toxic metabolites may cause abnormalities
in their weights. Gliricidia leaves contain some anti-nutrient
factors such as condensed tannins and cyanide (Chadhokar, 1982; Ahn et
al., 1989; Herbert, 1998). This may have accounted for the significantly
higher weights of the kidneys and liver of rabbits fed the 15 and 20%
GLM diets. Kidney fat weight decreased gradually but significantly as
the level of dietary GLM increased thus reflecting the effect of increasing
proportions of dietary fiber.
The findings of this study indicate that incorporation of GLM up to 20%
level in the diets of weaner rabbits does not significantly reduce tissue
synthesis in the rabbits. However, there is significant reduction in the
cost of feeding weaner rabbits in the tropics. This probably increases
detoxification activities in the liver and kidneys of rabbits when used
at levels beyond 10% in rabbit diets (Table 5).
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