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A feeding trial was conducted to investigate the effect of replacing maize with Threshed Rice Head (TRH) supplemented with and without enzyme on the nutrient digestibility of weaner rabbits. Fifty four rabbits were randomly allotted to six dietary treatments of three replicates. There were three rabbits per replicate in a 2 × 3 factorial arrangement in a completely randomized design. There were three inclusion levels (0, 7.5 and 15%) supplemented with and without enzyme in the diets. The response on TRH replacement showed that all the parameters measured (dry matter, crude protein, crude fibre, ether extract and ash) were significantly (P<0.05) affected by the test diets except nitrogen-free extract digestibility. The results showed that enzyme supplementation also had significant (P<0.05) effect on the coefficient of crude protein and crude fibre digestibility. The study indicated that TRH can be included in the diet of rabbit up to 15% with enzyme supplementation.
Keywords: Rabbits, Digestibility, Rice threshed head, Maize
There is a resultant increase in the demand for animal protein due to the rapid growth of human population in developing countries like Nigeria. Biobaku and Dosumu  reported that this observed low animal protein consumption may be attributed to the declining animal protein production in the country. Rabbit, as a micro-livestock, is an economic animal that can bridge the wide gap between dietary protein production and consumption in Nigeria. This is because rabbit has peculiar digestive physiology which permits the use of forages and agro-industrial by-products thus making it non-competitive specie with man for cereal and legume grains. According to Obeidat , sourcing for alternatives to the inadequate and expensive energy and protein feed stuffs like maize and soybean has become imperative since reducing production cost in order to maximize profit is the main objective of farmers. Researchers have shown over the years that different rice parts like the husk and bran during and after harvesting contain various nutrients that favor their use as animal feed. Proximate analysis of threshed rice head revealed relatively good values of crude protein (8.06%), crude fibre (13.15%), ash (4.18%), ether extract (2.68%), nitrogen free extract (66.41%) and metabolizable energy (2259.70 kcal/kg) at 92.48% dry matter content.
MATERIALS AND METHODS
Experimental animals, design and management
A total of 54 healthy five weeks old weaner rabbits were used in this study. They were randomly selected and allotted to six experimental diets in 2 × 3 factorial arrangement in a completely randomized design. There were three replicates per treatment and each replicate had three rabbits, comprising of nine animals per treatment. The rabbits were housed in a cage with wire meshed hutches. The cage was raised above the ground in a well-ventilated pen. Feed and water were supplied ad libitum.
Sources and processing of threshed rice head (TRH)
The threshed rice head was collected from rice farms in Gwagwalada, Abuja. After drying, the threshed rice head were crushed in a feed mill and sample was taken for proximate analysis before inclusion into the diets of the animals at various levels.
6 experimental diets were formulated with the Threshed Rice Head (TRH) with and without enzyme supplementation at different levels of replacement. Diets 1, 3 and 5 contained 0, 7.5 and 15% TRH without enzyme while diets 2, 4 and 6 contained 0, 7.5 and 15% TRH with enzyme supplementation. Maxi grain enzyme was used in this study.
At the end of the 8th week feeding trial, nutrient digestibility study was conducted. Rabbits closest to the average mean weight in each replicate were selected for the study. The rabbits were housed in a metabolic cage. Wire mesh was used to separate the feces and the urine was collected from the tray beneath the cage. Fecal samples were collected for a period of seven days. The feces were separated from feeds and other extraneous materials, sundried and bulked. The dried samples were then weighed, grinded and taken to the laboratory along with samples of feed for proximate analyses. Samples were analyzed for crude protein, crude fibre, ether extract, ash and nitrogen free extract. Nutrient retention was calculated with the formula:
(Nutrient intake - Nutrient output ÷ Nutrient intake) ×100
Data collected were subjected to statistical analysis using general linear model according to SAS . Significant differences were separated using Duncan’s multiple range tests .
RESULTS AND DISCUSSION
The data for nutrient digestibility of rabbits fed diets containing Threshed Rice Head (TRH) with and without enzyme supplementation as partial replacement for maize are presented in Table 1.
Rabbits fed 15% TRH level had higher coefficient of Crude Protein (CP), Crude Fibre (CF) and Ether Extract (EE) digestibility than those fed 0 and 7.5% TRH levels. Rabbits fed 0 and 15% levels of TRH had similar dry matter digestibility which were significantly (P<0.05) higher than that of 7.5% TRH level. However, there was no significant (P<0.05) difference in Nitrogen free extract digestibility across all TRH levels. Results on CP digestibility contradicts the reports of Adeniji  who fed bovine rumen content to rabbits and attributed the low CP digestibility to the high fibre content of the feed. The increased digestibility of ether extract with increased levels of TRH in the diets of the rabbits also disagrees with the result of Igwebuike  who reported that increased crude fibre levels in rabbit diets depresses ether extract digestibility. Nitrogen free extract digestibility was not significantly affected by the test material in the diets, thus, suggesting efficient utilization of soluble carbohydrates in all the diets. The result of this study is in line with the findings of Onifade  who reported high digestibility of readily available carbohydrates by rabbits in a feeding trial involving alternative tropical energy feed resources in rabbit diets. Generally, the results of this study disagrees with the submission of Alawa and Amadi  who reported that nutrient digestibility significantly decreases with increasing levels of dietary crude fibre. The results obtained in this study might be due to the fact that gut microorganisms in the digestive tract of the rabbits helped to properly degrade the fibrous content of the feed thereby making the nutrients available to the experimental animals. These better results proved that the fibre content of the feed at 15% TRH replacement was not beyond what the digestive system of the animals could handle.
The observed improvement in crude protein and crude fibre digestibility due to enzyme supplementation in this study is in line with the results of Gidenne and Jehl  who reported that enzyme supplementation reduces intestinal viscosity thereby improving contact between nutrients and digestive enzymes, thus, leading to improved digestibility coefficients. The enzyme supplementation results of this study are probably due to the enhanced effect of the exogenous enzymes on gut micro-flora and volatile fatty acids production thus resulting in improved nutrient digestibility. Even though Biobaku and Dosumu  earlier reported that enzyme supplementation had no effect on fibre digestion in rabbits, the higher crude protein and crude fibre digestibility in this study is in agreement with the report of Abaza and Omara  who observed similar results in fibre digestibility when corn cobs were supplemented with enzyme in the diet of growing rabbits. Adeyemo  also recently reported improved crude protein and crude fibre digestibility in rabbits fed enzyme supplemented diets. The interaction effects between enzyme supplementation and threshed rice head replacement was also significant showing that both the threshed rice head and the supplemented enzyme played roles in the nutrient digestibility of the animals.
It can be concluded that weaner rabbits can efficiently utilize TRH up to 15% in their diets especially when supplemented with enzyme.
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