Evaluation of the Effect of Replacing Maize with Cattle Rumen Waste Meal in Feed for Production of Nile Tilapia, Oreochromis Niloticus

: This study determined the nutritive values of cattle rumen waste (CRW) meal used for replacement of maize in the diets of Nile tilapia Oreochromis niloticus. CRW (20.9% CP) was used to replace maize (10.1 CP) at 0%, 25%, 50%, 75% and 100% making diets (D1-D5). The diets were fed to the fish (5.59±0.37g) to apparent satiation twice daily in three replicates. Results showed that the bacterial count of fresh CRW sample was 3.2 x 10 5 Cfu/g while the fungal count was 1.2 x 10 5 sfu/g, but after sun drying at constant moisture of 8.0%, the bacterial and fungal counts reduced by 90% and 100% respectively. The weight gain, specific growth rate and feed intake declined with increasing levels of CRM. Fish fed D1 had the best feed conversion ratio (FCR) of (1.29) while the group fed D5 gave the poorest FCR of (1.66). The results also revealed that increasing dietary levels of CRW resulted in marginal increase in carcass ash and fibre. The bacterial and fungal counts of fresh fish samples ranged between 2.4 x10 4 – 3.4 x10 4 Cfu/g and 0.4 x 10 4 – 1.5 x 10 4 Sfu/g, respectively, but the organisms disappeared after drying the fish at mean constant moisture of 6.21%. In conclusion, CRW can replace up to 50% of maize in the diets of Nile tilapia. The use of the rumen meal would reduce costs of fish production and increase the profit margin. It will also boost fish production and rural economy and serve as an economic means of environmental management.

Aquaculture has been described as a means of augmenting capture fisheries to boost fish food production. With intensification in aquaculture, the major problem is what to feed the fish since the same feed ingredients are used in human and livestocks feed resulting in increase in the prices of the conventional feedstuffs. This has implications that feed alone takes over 60% of the operating costs aquaculture (Nwanna, et al. 2014). According to Olurin et al. (2006) maize is the major source of metabolisable energy in most compounded diets for Tilapia species because it is readily available and digestible. But in the recent time, maize has become scarce due to environmental and socio-economic issues and the serious competition for its use between man and other livestocks, culminating in increases in the price of the commodity.
Cattle rumen wastes from abattoirs usually pose environmental and disposal problems. Preliminary investigations revealed that the rumen waste contains 18.5% protein and 38.4% carbohydrate (Esonu et al., 2006), an indication of its great potential as an energy source in tilapia nutrition. This study therefore investigated the nutritional values of cattle rumen waste and the effects of replacing maize with dried cattle rumen waste meal on the production of Nile tilapia.

MATERIALS AND METHODS
Sample collection: Fresh and hygienic cattle rumen waste was collected from the University Teaching and Research Farm of the Federal University of Technology Akure. The rumen collected was divided into two parts. A part of the rumen was used to determine the microbial load of the sample, while the other part was sun-dried to constant moisture content of 8.02% and then blended into powder form and sieved as the rumen waste meal.
Feed formulation/preparation: Five diets were formulated such that they contained the cattle rumen waste meal (CRW) at 0%, 25%, 50%, 75% and 100%, respectively, in replacement for yellow maize. The diets were stored at -20 o C before use.
Feeding trials: Four hundred (400) Oreochromis niloticus juveniles with mean weight of 5.59 ± 0.37g used for the study were acclimatized to laboratory conditions for two weeks. The experimental design was completely randomized. Out of the four hundred (400) fish, a total of Two hundred and twenty five (225) with mean weight of 5.59 ± 0.37g were 392 Evaluation of the Effect of Replacing Maize….. Nwanna, L; Oladipupo, M randomly selected and distributed into 15 glass Tanks measuring (70cmx45cmx45cm) representing five treatments and three replicates, at the rate of fifteen fish per tank. The experimental diets were administered to fish to apparent satiation, twice daily between 08:00 and 09:00 and 16:00 and 17:00 hours for 70days. After each feeding all uneaten feeds were removed one hour later. The water quality parameters (dissolved oxygen, pH and temperature were kept at optimum range recommended for warm water fishes Boyd, (1998). Evaluation of the growth performance was after Recker (1975) and Castell and Tiews (1980) while the protein efficiency ratio was calculated following the method of Stuart and Hung (1989).
Nutrient Agar (NA) and Sabouraud Dextrose Agar (SDA) were used as culture media for the determination of microbial loads according to the methods of (Pelczar et al., 1977). The culturing, incubating and colony count were carried out according to the methods of (Pelczar et al., 1977) while identification of the fungal and bacterial isolates was after (Domsch andGames 1970 andHolt et al. 1994) Data collection and analysis: Data collected were subjected to one-way analysis of variance as described by Steel and Torrie (1980) while means were separated using New Duncan multiple range test (Duncan, 1955).

RESULTS AND DISCUSSION
The results of the proximate composition of the rumen waste meal and maize used in the study (Table  1) reveal that protein content of rumen meal (20.9%) was more than double that of the maize and this value compare well with 18.7% reported by Esonu et al. (2006).
The lipid, ash and fibre contents of the rumen waste were much more than the values of maize. However, the carbohydrate content of maize was largely higher than that of the rumen waste.  The result also reveals that cattle rumen meal can be a good source of minerals for the fish. This will help to reduce the quantity of mineral supplement to the diet of the fish, and consequently the cost of mineral supplements and fish production will be reduced.
The growth performance and nutrients utilization parameters of O. niloticus fed cattle rumen waste meal (Table 3) indicates that the rumen meal can replace up to 50% of yellow maize in the diets without compromising physiological functions. This study also shows that cattle rumen waste was better utilized by Nile tilapia than duck weed which dietary inclusion level for the production of the fish was 15%, (Ofojekwu et al., (2010). The good utilization of cattle rumen meal, with relatively high fibre forage content might be due to the acidic nature of Tilapia stomach (pH<2) and presence of cellulase in the gut that facilitate the rupture of the cell wall of the vegetative matter (Fagbenro et al., 2005) and perhaps the action of unidentified single cell micro-flora such as fungi, bacteria on the rumen meal that might partially digest the forage prior to collection at the abattoir. According to De-Silva (2001) feed conversion ratio is between 1.2 -1.8 for fish fed carefully prepared diets, and the results from the present study are within this range. The proximate composition of the fish carcass (Table 4) reveals no significant differences (P>0.05) in the body composition of the fish after the experiment. The results also showed that, increasing dietary levels of cattle rumen waste meal resulted in a Total Variable Counts (TVC) for bacteria and fungi isolates from fresh fish reveals that the flesh had a total bacteria count reaching 2.9 x 10 4 , with the total fungi count reaching 1.0 x 10 4 , and these bacterial and fungal loads are within the tolerable range recommended by the International Commission for Microbiological Standards of Food (ICMSF, 1978).
After smoke drying at mean constant moisture content of 6.21%, no bacteria and fungi species were detected in the fish samples, and this supports the works of Garcia et al (2005) and Bilgin et al. (2008) who reported drastic reduction in microbial load of fish samples after drying. In conclusion, the use of Cattle rumen waste meal will reduce the costs of fish production by sparing 50% of maize and reducing the quantity and costs of mineral supplementation in the diets.